The Selection of an Acetylene Generator · Acetylene, the Principles of Its Generation and Use

Acetylene, the Principles of Its Generation and Use · Chapter 12The Selection of an Acetylene Generator

This chapter is not translated yet. You are reading the original.

Chapter IV

In Chapter II. an attempt has been made to explain the physical and chemical phenomena which accompany the interaction of calcium carbide and water, and to show what features in the reaction are useful and what inconvenient in the evolution of acetylene on a domestic or larger scale. Similarly in Chapter III. have been described the various typical devices which may be employed in the construction of different portions of acetylene plant, so that the gas may be generated and stored under the best conditions, whether it is evolved by the automatic or by the non- automatic system. This having been done, it seemed of doubtful utility to include in the first edition of this work a long series of illustrations of such generators as had been placed on the markets by British, French, German, and American makers. It would have been difficult within reasonable limits to have reproduced diagrams of all the generators that had been offered for sale, and absolutely impossible within the limits of a single hand-book to picture those which had been suggested or patented. Moreover, some generating apparatus appeared on the market ephemerally; some was constantly being modified in detail so as to alter parts which experience or greater knowledge had shown the makers to be in need of alteration, while other new apparatus was constantly being brought out. On these and other grounds it did not appear that much good purpose would have been served by describing the particular apparatus which at that time would have been offered to prospective purchasers. It seemed best that the latter should estimate the value and trustworthiness of apparatus by studying a section of it in the light of the general principles of construction of a satisfactory generator as enunciated in the book. While the position thus taken by the authors in 1903 would still not be incorrect, it has been represented to them that it would scarcely be inconsistent with it to give brief descriptions of some of the generators which are now being sold in Great Britain and a few other countries. Six more years' experience in the design and manufacture of acetylene plant has enabled the older firms of manufacturers to fix upon certain standard patterns for their apparatus, and it may confidently be anticipated that many of these will survive a longer period. Faulty devices and designs have been weeded out, and there are lessons of the past as well as theoretical considerations to guide the inventor of a new type of generator. On those grounds, therefore, an attempt has now been made to give brief descriptions, with sectional views, of a number of the generators now on the market in Great Britain. Moreover, as the first edition of this book found many readers in other countries, in several of which there is greater scope for the use of acetylene, it has been decided to describe also a few typical or widely used foreign generators. All the generators described must stand or fall on their merits, which cannot be affected by any opinion expressed by the authors. In the descriptions, which in the first instance have generally been furnished by the manufacturers of the apparatus, no attempt has therefore been made to appraise the particular generators, and comparisons and eulogistic comments have been excluded. The descriptions, however, would nevertheless have been somewhat out of place in the body of this book; they have therefore been relegated to a special Appendix. It has, of course, been impossible to include the generators of all even of the English manufacturers, and doubtless many trustworthy ones have remained unnoticed. Many firms also make other types of generators in addition to those described. It must not be assumed that because a particular make of generator is not mentioned it is necessarily faulty. The apparatus described may be regarded as typical or well known, and workable, but it is not by reason of its inclusion vouched for in any other respect by the authors. The Appendix is intended, not to bias or modify the judgment of the would-be purchaser of a generator, but merely to assist him in ascertaining what generators there are now on the market.

The observations on the selection of a generator which follow, as well as any references in other chapters to the same matter, have been made without regard to particular apparatus of which a description may (or may not) appear in the Appendix. With this premise, it may be stated that the intending purchaser should regard the mechanism of a generator as shown in a sectional view or on inspection of the apparatus itself. If the generator is simple in construction, he should be able to understand its method of working at a glance, and by referring it to the type (vide Chapter III.) to which it belongs, be able to appraise its utility from a chemical and physical aspect from what has already been said. If the generator is too complicated for ready understanding of its mode of working, it is not unlikely to prove too complicated to behave well in practice. Not less important than the mechanism of a generator is good construction from the mechanical point of view, i.e., whether stout metal has been employed, whether the seams and joints are well finished, and whether the whole apparatus has been built in the workman- like fashion which alone can give satisfaction in any kind of plant. Bearing these points in mind, the intending purchaser may find assistance in estimating the mechanical value of an apparatus by perusing the remainder of this chapter, which will be devoted to elaborating at length the so-called scientific principles underlying the construction of a satisfactory generator, and to giving information on the mechanical and practical points involved.

It is perhaps desirable to remark that there is scarcely any feature in the generation of acetylene from calcium carbide and water--certainly no important feature--which introduces into practice principles not already known to chemists and engineers. Once the gas is set free it ranks simply as an inflammable, moisture-laden, somewhat impure, illuminating and heat-giving gas, which has to be dried, purified, stored, and led to the place of combustion; it is in this respect precisely analogous to coal- gas. Even the actual generation is only an exothermic, or heat-producing, reaction between a solid and a liquid, in which rise of temperature and pressure must be prevented as far as possible. Accordingly there is no fundamental or indispensable portion of an acetylene apparatus which lends itself to the protection of the patent laws; and even the details (it may be said truthfully, if somewhat cynically) stand in patentability in inverse ratio to their simplicity and utility.

During the early part of 1901 a Committee appointed by the British Home Office, "to advise as to the conditions of safety to which acetylene generators should conform, and to carry out tests of generators in the market in order to ascertain how far those conform with such conditions," issued a circular to the trade suggesting that apparatus should be sent them for examination. In response, forty-six British generators were submitted for trial, and were examined in a fashion which somewhat exceeded the instructions given to the Committee, who finally reported to the Explosives Department of the Home Office in a Blue Book, No. Cd. 952, which can be purchased through any bookseller. This report comprises an appendix in which most of the apparatus are illustrated, and it includes the result of the particular test which the Committee decided to apply. Qualitatively the test was useful, as it was identical in all instances, and only lacks full utility inasmuch as the trustworthiness of the automatic mechanism applied to such generators as were intended to work on the automatic system was not estimated. Naturally, a complete valuation of the efficiency of automatic mechanism cannot be obtained from one or even several tests, it demands long-continued watching; but a general notion of reliability might have been obtained. Quantitatively, however, the test applied by the Committee is not so free from reproach, for, from the information given, it would appear to have been less fair to some makers of apparatus than to others. Nevertheless the report is valuable, and indicates the general character of the most important apparatus which were being offered for sale in the United Kingdom in 1900-1901.

It is not possible to give a direct answer to the question as to which is the best type of acetylene generator. There are no generators made by responsible firms at the present time which are not safe. Some may be easier to charge and clean than others; some require more frequent attention than others; some have moving parts less likely to fail, when handled carelessly, than others; some have no moving mechanism to fail. For the illumination of a large institution or district where one man can be fully occupied in attending to the plant, cleaning, lighting, and extinguishing the lamps, or where other work can be found for him so as to leave him an hour or so every day to look after the apparatus, the hand-fed carbide-to-water generator L (Fig. 6) has many advantages, and is probably the best of all. In smaller installations choice must be made first between the automatic and the non-automatic principle--the advantages most frequently lying with the latter. If a non-automatic generator is decided upon, the hand carbide-feed or the flooded- compartment apparatus is almost equally good; and if automatism is desired, either a flooded-compartment machine or one of the most trustworthy types of carbide-feed apparatus may be taken. There are contact apparatus on the markets which appear never to have given trouble, and those are worthy of attention. Some builders advocate their own apparatus because the residue is solid and not a cream. If there is any advantage in this arising from greater ease in cleaning and recharging the generator and in disposing of the waste, that advantage is usually neutralised by the fear that the carbide may not have been wholly decomposed within the apparatus; and whereas any danger arising from imperfectly spent carbide being thrown into a closed drain may be prevented by flooding the residue with plenty of water in an open vessel, imperfect decomposition in the generator means a deficiency in the amount of gas evolved from a unit weight of solid taken or purchased. In fact, setting on one side apparatus which belong to a notoriously defective system and such as are constructed in large sizes on a system that is only free from overheating, &c., in small sizes; setting aside all generators which are provided with only one decomposing chamber when they are of a capacity to require two or more smaller ones that can more efficiently be cooled with water jackets; and setting aside any form of plant which on examination is likely to exhibit any of the more serious objections indicated in this and the previous chapters, there is comparatively little to choose, from the chemical and physical points of view, between the different types of generators now on the markets. A selection may rather be made on mechanical grounds. The generator must be well able to produce gas as rapidly as it will ever be required during the longest or coldest evening; it must be so large that several more brackets or burners can be added to the service after the installation is complete. It must be so strong that it will bear careless handling and the frequent rough manipulation of its parts. It must be built of stout enough material not to rust out in a few years. Each and all of its parts must be accessible and its exterior visible. Its pipes, both for gas and sludge, must be of large bore (say 1 inch), and fitted at every dip with an arrangement for withdrawing into some closed vessel the moisture, &c., that may condense. The number of cocks, valves, and moving parts must be reduced to a minimum; cocks which require to be shut by hand before recharging must give way to water-seals. It must be simple in all its parts, and its action intelligible at a glance. It must be easy to charge--preferably even by the sense of touch in darkness. It must be easy to clean. The waste lime must be easily removed. It must be so fitted with vent-pipes that the pressure can never rise above that at which it is supposed to work. Nevertheless, a generator in which these vent-pipes are often brought into use is badly constructed and wasteful, and must be avoided. The water of the holder seal should be distinct from that used for decomposing the carbide; and those apparatus where the holder is entirely separated from the generator are preferable to such as are built all in one, even if water-seals are fitted to prevent return of gas. Apparatus which is supposed to be automatic should be made perfectly automatic, the water or the carbide-feed being locked automatically before the carbide store, the decomposing chamber, or the sludge-cock can be opened. The generating chamber must always be in communication with the atmosphere through a water-sealed vent-pipe, the seal of which, if necessary, the gas can blow at any time. All apparatus should be fitted with rising holders, the larger the better. Duplicate copies of printed instructions should be demanded of the maker, one copy being kept in the generator-house, and the other elsewhere for reference in emergencies. These instructions must give simple and precise information as to what should be done in the event of a breakdown as well as in the normal manipulation of the plant. Technical expressions and descriptions of parts understood only by the maker must be absent from these rules.

ADDENDUM.

BRITISH AND FOREIGN REGULATIONS FOR THE CONSTRUCTION AND INSTALLATION OF ACETYLENE GENERATING PLANT

Dealing with the "conditions which a generator should fulfil before it can be considered as being safe," the HOME OFFICE COMMITTEE of 1901 before mentioned write as follows:

1. The temperature in any part of the generator, when run at the maximum rate for which it is designed, for a prolonged period, should not exceed 130° C. This may be ascertained by placing short lengths of wire, drawn from fusible metal, in those parts of the apparatus in which heat is liable to be generated.

2. The generator should have an efficiency of not less than 90 per cent., which, with carbide yielding 5 cubic feet per pound, would imply a yield of 4.5 cubic feet for each pound of carbide used.

3. The size of the pipes carrying the gas should be proportioned to the maximum rate of generation, so that undue back pressure from throttling may not occur.

4. The carbide should be completely decomposed in the apparatus, so that lime sludge discharged from the generator shall not be capable of generating more gas.

5. The pressure in any part of the apparatus, on the generator side of the holder, should not exceed that of 20 inches of water, and on the service side of same, or where no gasholder is provided, should not exceed that of 5 inches of water.

6. The apparatus should give no tarry or other heavy condensation products from the decomposition of the carbide.

7. In the use of a generator regard should be had to the danger of stoppage of passage of the gas and resulting increase of pressure which may arise from the freezing of the water. Where freezing may be anticipated, steps should be taken to prevent it.

8. The apparatus should be so constructed that no lime sludge can gain access to any pipes intended for the passage of gas or circulation of water.

9. The use of glass gauges should be avoided as far as possible, and, where absolutely necessary, they should be effectively protected against breakage.

10. The air space in a generator before charging should be as small as possible.

11. The use of copper should be avoided in such parts of the apparatus as are liable to come in contact with acetylene.

The BRITISH ACETYLENE ASSOCIATION has drawn up the following list of regulations which, it suggests, shall govern the construction of generators and the installation of piping and fittings:

1. Generators shall be so constructed that, when used in accordance with printed instructions, it shall not be possible for any undecomposed carbide to remain in the sludge removed therefrom.

2. The limit of pressure in any part of the generator shall not exceed that of 20 inches of water, subject to the exception that if it be shown to the satisfaction of the Executive of the Acetylene Association that higher pressures up to 50 inches of water are necessary in certain generators, and are without danger, the Executive may, with the approval of the Home Office, grant exemption for such generators, with or without conditions.

3. The limit of pressure in service-pipes, within the house, shall not exceed 10 inches of water.

4. Except when used for special industrial purposes, such as oxy- acetylene welding, factories, lighthouses, portable apparatus containing not more than four pounds of carbide, and other special conditions as approved by the Association, the acetylene plant, such as generators, storage-holders, purifiers, scrubbers, and for washers, shall be in a suitable and well-ventilated outhouse, in the open, or in a lean-to, having no direct communication with a dwelling-house. A blow-off pipe or safety outlet shall be arranged in such a manner as to carry off into the open air any overmake of gas and to open automatically if pressure be increased beyond 20 inches water column in the generating chamber or beyond 10 inches in the gasholder, or beyond the depth of any fluid seal on the apparatus.

5. Generators shall have sufficient storage capacity to make a serious blow-off impossible.

6. Generators and apparatus shall be made of sufficiently strong material and be of good workmanship, and shall not in any part be constructed of unalloyed copper.

7. It shall not be possible under any conditions, even by wrong manipulation of cocks, to seal the generating chamber hermetically.

8. It shall not be possible for the lime sludge to choke any of the gas- pipes in the apparatus, nor water-pipes if such be alternately used as safety-valves.

9. In the use of a generator, regard shall be had to the danger of stoppage of passage of the gas, and resulting increase of pressure, which may arise from the freezing of the water. Where freezing may be anticipated, steps shall be taken to prevent it.

10. The use of glass gauges shall be avoided as far as possible, and where absolutely necessary they shall be effectively protected against breakage.

11. The air space in the generator before charging shall be as small as possible, i.e., the gas in the generating chamber shall not contain more than 8 per cent. of air half a minute after commencement of generation. A sample of the contents, drawn from the holder any time after generation has commenced, shall not contain an explosive mixture, i.e., more than 18 per cent, of air. This shall not apply to the initial charges of the gasholder, when reasonable precautions are taken.

12. The apparatus shall produce no tarry or other heavy condensation products from the decomposition of the carbide.

13. The temperature of the gas, immediately on leaving the charge, shall not exceed 212° F. (100° C.)

14. No generator shall be sold without a card of instructions suitable for hanging up in some convenient place. Such instructions shall be of the most detailed nature, and shall not presuppose any expert knowledge whatever on the part of the operator.

15. Notice to be fixed on Generator House Door, "NO LIGHTS OR SMOKING ALLOWED."

16. Every generator shall have marked clearly upon the outside a statement of the maximum number of half cubic foot burners and the charge of carbide for which it is designed.

17. The Association strongly advise the use of an efficient purifier with generating plant for indoor lighting.

18. No composition piping shall be used in any part of a permanent installation.

19. Before being covered in, all pipe-work (main and branches) shall be tested in the following manner: A special acetylene generator, giving a pressure of at least 10 inches water column in a gauge fixed on the furthest point from the generator, shall be connected to the pipe-work. All points shall be opened until gas reaches them, when they shall be plugged and the main cock on the permanent generator turned off, but all intermediate main cocks shall be open in order to test underground main and all connexions. The gauge must not show a loss after generator has been turned off for at least two hours.

20. After the fittings (pendants, brackets, &c.) have been fixed and all burners lighted, the gas shall be turned off at the burners and the whole installation shall be re-tested, but a pressure of 5 inches shall be deemed sufficient, which shall not drop lower than to 4-1/2 inches on the gauge during one hour's test.

21. No repairs to, or alterations in, any part of a generator, purifier, or other vessel which has contained acetylene shall be commenced, nor, except for recharging, shall any such part or vessel be cleaned out until it has been completely filled with water, so as to expel any acetylene or mixture of acetylene and air which may remain in the vessel, and may cause a risk of explosion.

Recommendation.--It being the general practice to store carbide in the generator-house, the Association recommend that the carbide shall be placed on a slightly raised platform above the floor level.

THE BRITISH FIRE OFFICES COMMITTEE in the latest revision, dated July 15, 1907, of its Rules and Regulations re artificial lighting on insured premises, includes the following stipulations applicable to acetylene:

Any apparatus, except as below, for generating, purifying, enriching, compressing or storing gas, must be either in the open or in a building used for such purposes only, not communicating directly with any building otherwise occupied.

An acetylene portable apparatus is allowed, provided it holds a charge of not more than 2 lb. of carbide.

A cylinder containing not more than 20 cubic feet of acetylene compressed and (or) dissolved in accordance with an Order of Secretary of State under the Explosives Act, 1875, is allowed.

The use of portable acetylene lamps containing charges of carbide exceeding the limit of 2 lb. allowed under these Rules (the average charge being about 18 lb.) is allowed in the open or in buildings in course of erection.

Liquid acetylene must not be used or stored on the premises.

The pipe, whether flexible or not, connecting an incandescent gas lamp to the gas-supply must be of metal with metal connexions.

(The reference in these Rules to the storage of carbide has been quoted in Chapter II. (page 19).)

These rules are liable to revision from time to time.

The GERMAN ACETYLENE VEREIN has drawn up (December 1904) the following code of rules for the construction, erection, and manipulation of acetylene apparatus:

I. Rules for Construction.

1. All apparatus for the generation, purification, and storage of acetylene must be constructed of sheet or cast iron. Holder tanks may be built of brick.

2. When bare, galvanised, or lead-coated sheet-iron is used, the sides of generators, purifiers, condensers, holder tanks, and (if present) washers and driers must be built with the following gauges as minima:

Holder bells. All other apparatus. Up to 7 cubic feet capacity 0.75 mm. 1.00 mm. From 7 to 18 " 1.00 1.25 From 18 to 53 " 1.25 1.50 Above 53 " 1.50 2.00

When not constructed of cast-iron, the bottoms, covers, and "manhole" lids must be 0.5 mm. thicker in each respective size.

In all circumstances, the thickness of the walls--especially in the case of apparatus not circular in horizontal section--must be such that alteration in shape appears impossible, unless deformation is guarded against in other ways.

Generators must be so constructed that when they are being charged the carbide cannot fall into the residue which has already been gasified; and the residues must always be capable of easy, complete, and safe removal.

3. Generators, purifiers, and holders must be welded, riveted or folded at the seams; soft solder is only permissible as a tightening material.

4. Pipes delivering acetylene, or uniting the apparatus, must be cast- or wrought-iron. Unions, cocks, and valves must not be made of copper; but the use of brass and bronze is permitted.

5. When cast-iron is employed, the rules of the German Gas and Water Engineers are to be followed.

6. In generators where the whole amount of carbide introduced is not gasified at one time, it must be possible to add fresh water or carbide in safety, without interfering with the action of the apparatus. In such generators the size of the gasholder space is to be calculated according to the quantity of carbide which can be put into the generator. For every 1 kilogramme of carbide the available gasholder space must be: for the first 50 kilos., 20 litres; for the next 50 kilos., 15 litres; for amounts above 100 kilos., 10 litres per kilo. [One kilogramme may be taken as 2.2 lb., and 28 litres as 1 cubic foot.]

The generator must be large enough to supply the full number of normal (10-litre) burners with gas for 5 hours; the yield of acetylene being taken at 290 litres per kilo. [4.65 cubic feet per lb.]

The gasholder space of apparatus where carbide is not stored must be at least 30 litres for every normal (10-litre) flame.

7. The gasholder must be fitted with an appliance for removing any gas which may be generated (especially when the apparatus is first brought into action) after the available space is full. This vent must have a diameter at least equal to the inlet pipe of the holder.

8. Acetylene plant must be provided with purifying apparatus which contains a proper purifying material in a suitable condition.

9. The dimensions of subsidiary apparatus, such as washers, purifiers, condensers, pipes, and cocks must correspond with the capacity of the plant.

10. Purifiers and washers must be constructed of materials capable of resisting the attack of the substances in them.

11. Every generator must bear a plate giving the name of the maker, or the seller, and the maximum number of l0-litre lights it is intended to supply. If all the carbide put into the generator is not gasified at one time, the plate must also state the maximum weight of carbide in the charge. The gasholder must also bear a plate recording the maker's or seller's name, as well as its storage capacity.

12. Rules 1 to 11 do not apply to portable apparatus serving up to two lights, or to portable apparatus used only out of doors for the lighting of vehicles or open spaces.

II. Rules for Erection

1. Acetylene apparatus must not be erected in or under rooms occupied or frequented (passages, covered courts, &c.) by human beings. Generators and holders must only be erected in apartments covered with light roofs, and separated from occupied rooms, barns, and stables by a fire-proof wall, or by a distance of 15 feet. Any wall is to be considered fire- proof which is built of solid brick, without openings, and one side of which is "quite free." Apparatus may be erected in barns and stables, provided the space required is partitioned off from the remainder by a fire-proof wall.

2. The doors of apparatus sheds must open outwards, and must not communicate directly with rooms where fires and artificial lights are used.

3. Apparatus for the illumination of showmen's booths, "merry-go-rounds," shooting galleries, and the like must be erected outside the tents, and be inaccessible to the public.

4. Permanent apparatus erected in the open air must be at least 15 feet from an occupied building.

5. Apparatus sheds must be fitted at their highest points with outlet ventilators of sufficient size; the ventilators leading straight through the roof into the open air. They must be so arranged that the escaping gases and vapours cannot enter rooms or chimneys.

6. The contacts of any electrical warning devices must be outside the apparatus shed.

7. Acetylene plants must be prevented from freezing by erection in frost- free rooms, or by the employment of a heating apparatus or other suitable appliance. The heat must only be that of warm water or steam. Furnaces for the heating appliance must be outside the rooms containing generators, their subsidiary apparatus, or holders; and must be separated from such rooms by fire-proof walls.

8. In one of the walls of the apparatus shed--if possible not that having a door--a window must be fitted which cannot be opened; and outside that window an artificial light is to be placed. In the usual way acetylene lighting may be employed; but a lamp burning paraffin or oil, or a lantern enclosing a candle, must always be kept ready for use in emergencies. In all circumstances internal lighting is forbidden.

9. Every acetylene installation must be provided with a main cock, placed in a conveniently accessible position so that the whole of the service may be cut off from the plant.

10. The seller of an apparatus must provide his customer with a sectional drawing, a description of the apparatus, and a set of rules for attending to it. These are to be supplied in duplicate, and one set is to be kept hanging up in the apparatus shed.

III. Rules for Working the Apparatus.

1. The apparatus must only be opened by daylight for addition of water. If the generator is one of those in which the entire charge of carbide is not gasified at once, addition of fresh carbide must only be made by daylight.

2. All work required by the plant, or by any portion of it, and all ordinary attendance needed must be performed by daylight.

3. All water-seals must be carefully kept full.

4. When any part of an acetylene apparatus or a gas-meter freezes, notwithstanding the precautions specified in II., 7, it must be thawed only by pouring hot water into or over it; flames, burning fuel, or red- hot iron bars must not be used.

5. Alterations to any part of an apparatus which involve the operations of soldering or riveting, &c., i.e., in which a fire must be used, or a spark may be produced by the impact of hammer on metal, must only be carried out by daylight in the open air after the apparatus has been taken to pieces. First of all the plant must be freed from gas. This is to be done by filling every part with water till the liquid overflows, leaving the water in it for at least five minutes before emptying it again.

6. The apparatus house must not be used for any other operation, nor employed for the storage of combustible articles. It must be efficiently ventilated, and always kept closed. A notice must be put upon the door that unauthorised persons are not permitted to enter.

7. It in forbidden to enter the house with a burning lantern or lamp, to strike matches, or to smoke therein.

8. A search for leaks in the pipes must not be made with the aid of a light.

9. Alterations to the service must not be made while the pipes are under pressure, but only after the main cock has been shut.

10. If portable apparatus, such as described in I., 12, are connected to the burners with rubber tube, the tube must be fortified with an internal or external spiral of wire. The tube must be fastened at both ends to the cocks with thread, copper wire, or with ring clamps.

11. The preparation, storage, and use of compressed or liquefied acetylene is forbidden. By compressed acetylene, however, is only to be understood gas compressed to a pressure exceeding one effective atmosphere. Acetylene compressed into porous matter, with or without acetone, is excepted from this prohibition.

12. In the case of plants serving 50 lights or less, not more than 100 kilos. of carbide in closed vessels may be kept in the apparatus house besides the drum actually in use.

A fresh drum is not to be opened before the previous one has been two- thirds emptied. Opened drums must be closed with an iron watertight lid covering the entire top of the vessel.

In the case of apparatus supplying over 500 lights, only one day's consumption of carbide must be kept in the generator house. In other respects the store of carbide for such installations is to be treated as a regular carbide store.

13. Carbide drums must not be opened with the aid of a flame or a red-hot iron instrument.

14. Acetylene apparatus must only be attended to by trustworthy and responsible persons.

The rules issued by the AUSTRIAN GOVERNMENT in 1905 for the installation of acetylene plant and the use of acetylene are divided into general enactments relating to acetylene, and into special enactments in regard to the apparatus and installation. The general enactments state that:

1. The preparation and use of liquid acetylene is forbidden.

2. Gaseous acetylene, alone, in admixture, or in solution, must not be compressed above 2 atmospheres absolute except under special permission.

3. The storage of mixtures of acetylene with air or other gases containing or evolving free oxygen is forbidden.

4. A description of every private plant about to be installed must be submitted to the local authorities, who, according to its size and character, may give permission for it to be installed and brought into use either forthwith or after special inspection. Important alterations to existing plant must be similarly notified.

5. The firms and fitters undertaking the installation of acetylene plant must be licensed.

The special enactments fall under four headings, viz., (a) apparatus; (b) plant houses; (c) pipes; (d) residues.

In regard to apparatus it is enacted that:

1. The type of apparatus to be employed must be one which has been approved by one of certain public authorities in the country.

2. A drawing and description of the construction of the apparatus and a short explanation of the method of working it must be fixed in a conspicuous position under cover in the apparatus house. The notice must also contain approved general information as to the properties of calcium carbide and acetylene, precautions that must be observed to guard against possible danger, and a statement of how often the purifier will require to be recharged.

3. The apparatus must be marked with the name of the maker, the year of its construction, the available capacity of the gasholder, and the maximum generating capacity per hour.

4. Each constituent of the plant must be proportioned to the maximum hourly output of gas and in particular the available capacity of the holder must be 75 per cent. of the latter. The apparatus must not be driven above its nominal productive capacity.

5. The productive capacity of generators in which the gasholder has to be opened or the bell removed before recharging, or for the removal of sludge, must not exceed 50 litres per hour, nor may the charge of carbide exceed 1 kilo.

6. Generators exceeding 50 litres per hour productive capacity must be arranged so that they can be freed from air before use.

7. Generators exceeding 1500 litres per hour capacity must be arranged so that the acetylene, contained in the parts of the apparatus which have to be opened for recharging or for the removal of sludge, can be removed before they are opened.

8. Automatic generators of which the decomposing chambers are built inside the gasholder must not exceed 300 litres per hour productive capacity.

9. Generators must be arranged so that after-generation cannot produce objectionable results.

10. The holder of carbide-to-water generators must be large enough to take all the gas which may be produced by the introduction of one charge of carbide without undue pressure ensuing.

11. The maximum pressure permissible in any part of the apparatus is 1.1 atmosphere absolute.

12. The temperature in the gas space of a generator must never exceed 80° C.

13. Generating apparatus, &c., must be constructed in a workmanlike manner of metal capable of resisting rust and distortion, and, where the metal comes in contact with carbide or acetylene, it must not be one (copper in particular) which forms an explosive compound with the gas. Cocks and screw connexions, &c., of brass, bronze, &c., must always be kept clean. Joints exposed to acetylene under pressure must be made by riveting or welding except that in apparatus not exceeding 100 litres per hour productive capacity double bending may be used.

14. Every apparatus must be fitted with a safety-valve or vent-pipe terminating in a safe place in the open, and of adequate size.

15. Every apparatus must be provided with an efficient purifier so fitted that it may be isolated from the rest of the plant and with due consideration of the possible action of the purifying material upon the metal used.

16. Mercury pressure gauges are prohibited. Liquid gauges, if used must be double the length normally needed, and with a cock which in automatic apparatus must be kept shut while it is in action.

17. Proper steps must always be taken to prevent the apparatus freezing. In the absence of other precautions water-seals and pressure-gauges must be filled with liquid having a sufficiently low freezing-point and without action on acetylene or the containing vessel.

18. Signal devices to show the position of the gasholder bell must not be capable of producing sparks inside the apparatus house.

19. Leaks must not be sought for with an open flame and repairs requiring the use of a blow-pipe, &c., must only be carried out after the apparatus has been taken to pieces or freed from gas by flooding.

20. Apparatus must only be attended to by trustworthy and responsible adults.

21. Portable apparatus holding not more than 1 kilo. of carbide and of not more than 50 litres per hour productive capacity, and apparatus fixed and used out of doors are exempt from the foregoing regulations except Nos. 11 and 12, and the first part of 13.

In regard to (b), plant houses, it is enacted that:

1. Rooms containing acetylene apparatus must be of ample size, used for no other purpose, have water-tight floors, be warmed without fireplaces or chimneys, be lighted from outside through an air-tight window by an independent artificial light, have doors opening outwards, efficient ventilation and a store of sand or like material for fire extinction. Strangers must be warned away.

2. Apparatus of not more than 300 litres per hour productive capacity may be erected in basements or annexes of dwelling houses, but if of over 50 litres per hour capacity must not be placed under rooms regularly frequented. Rooms regularly frequented and those under the same must not be used.

3. Apparatus of more than 300 litres per hour productive capacity must be erected in an independent building at least 15 feet distant from other property, which building, unless it is at least 30 feet distant, must be of fire-proof material externally.

4. Gasholders exceeding 280 cubic foot in capacity must be in a detached room or in the open and inaccessible to strangers, and at least 30 feet from other property and with lightning conductors.

5. In case of fire the main cock must not be shut until it is ascertained that no one remains in the room served with the gas.

6. All acetylene installations must be known to the local fire brigade.

In regard to (c), pipes, it is enacted that:

1. Mains for acetylene must be separated from the generating apparatus by a cock, and under a five-minute test for pressure must not show a fall of over eight-tenths inch when the pressure is 13.8 inches, or three times the working pressure, whichever is greater.

2. The pipes must as a rule be of iron, though lead may be used where they are uncovered and not exposed to risk of injury. Rubber connexions may only be used for portable apparatus, and attached to a terminal on the metal pipes provided with a cock, and be fastened at both ends so that they will not slip off the nozzles.

In regard to (d), residues, it is enacted that special open or well-ventilated pits must be provided for their reception when the apparatus exceeds 300 litres per hour productive capacity. With smaller apparatus they may be discharged into cesspools if sufficiently diluted. The ITALIAN GOVERNMENT regulations in regard to acetylene plant are divided into eight sections. The first of these relates to the production and use of liquid and compressed acetylene. The production and use of liquid acetylene is prohibited except under the provisions of the laws relating to explosives. Neat acetylene must not be compressed to more than l-1/2 atmospheres except that an absolute pressure of 10 atmospheres is allowed when the gas is dissolved in acetone or otherwise rendered free from risk. Mixtures of acetylene with air or oxygen are forbidden, irrespective of the pressure or proportions. Mixtures of acetylene with hydrocarbons, carbonic oxide, hydrogen and inert gases are permitted provided the proportion of acetylene does not exceed 50 per cent. nor the absolute pressure 10 atmospheres.

The second section relates to acetylene installations, which are classified in four groups, viz., (a) fixed or portable apparatus supplying not more than thirty burners consuming 20 litres per hour; (b) private installations supplying between 30 and 200 such burners; (c) public or works installations supplying between 30 and 200 such burners; (d) installations supplying more than 200 such burners.

The installations must comply with the following general conditions:

1. No part of the generator when working at its utmost capacity should attain a temperature of more than 100° C.

2. The carbide must be completely decomposed in the apparatus so that no acetylene can be evolved from the residue. The residues must be diluted with water before being discharged into drains or cesspools, and sludge storage-pits must be in the open.

3. The apparatus must preclude the escape of lime into the gas and water connexions.

4. Glass parts must be adequately protected.

5. Rubber connexions between the generator, gasholder, and main are absolutely prohibited with installations supplying more than 30 burners.

6. Cocks must be provided for cutting off the main and connexions from the generator and gasholder.

7. Each burner must have an independent tap.

8. Generators of groups (b), (c), and (d) must be constructed so that no after-generation of acetylene can take place automatically and that any surplus gas would in any case be carried out of the generator house by a vent-pipe.

The third section deals with generator houses, which must be well ventilated and light; must not be used for any other purpose except to store one day's consumption of carbide, not exceeding 300 kilos.; must be fire-proof; must have doors opening outwards; and the vent-pipes must terminate at a safe place in the open. Apparatus of group (b) must not be placed in a dwelling-room and only in an adjoining room if the gasholder is of less than 600 litres capacity. Apparatus of group (c) must be in an independent building which must be at least 33 feet from occupied premises if the capacity of the gasholder is 6000 litres and upwards. Half this distance suffices for gasholders containing 600 to 6000 litres. These distances may be reduced at the discretion of the local authorities provided a substantial partition wall at least 1 foot thick is erected. Apparatus of group (d) must be at least 50 feet from occupied premises and the gasholder and generator must not be in the same building.

The fourth section deals with the question of authorisation for the installation of acetylene plant. Apparatus of group (a) may be installed without obtaining permission from any authorities. In regard to apparatus of the other groups, permission for installation must be obtained from local or other authorities.

The fifth section relates to the working of acetylene plant. It makes the concessionaires and owners of the plant responsible for the manipulation and supervision of the apparatus, and for the employment of suitable operators, who must not be less than 18 years of age.

The sixth section relates to the inspection of acetylene plant from time to time by inspectors appointed by the local or other authorities. Apparatus of group (a) is not subject to these periodical inspections.

The seventh section details the fees payable for the inspection of installations and carbide stores, and fixes the penalties for non- compliance with the regulations.

The eighth section refers to the notification of the position and description of all carbide works, stores, and acetylene installations to the local authorities.

The HUNGARIAN GOVERNMENT rules for the construction and examination of acetylene plant forbid the use of copper and of its alloys; cocks, however, may be made of a copper alloy. The temperature in the gas space of a fixed generator must not exceed 50° C., in that of a portable apparatus 80° C. The maximum effective pressure permissible is 0.15 atmosphere.

The CONSEIL D'HYGIÈNE DE LA SEINE IN FRANCE allows a maximum pressure of 1.5 metres, i.e., 59 inches, of water column in generators used for the ordinary purposes of illumination; but apparatus intended to supply gas to the low-pressure oxy-acetylene blowpipe (see Chapter IX.) may develop up to 2.5 metres, or 98.5 inches of water pressure, provided copper and its alloys are entirely excluded from the plant and from the delivery- pipes.

The NATIONAL BOARD OF FIRE UNDERWRITERS OF THE UNITED STATES OF AMERICA has issued a set of rules and requirements, of which those relating to acetylene generators and plant are reproduced below. The underwriters state that, "To secure the largest measure of safety to life and property, these rules for the installation of acetylene gas machines must be observed."

RULES FOR THE INSTALLATION AND USE OF ACETYLENE GAS GENERATORS. [Footnote: The "gallon" of these rules is, of course, the American gallon, which is equal to 0.83 English standard gallon.]

The use of liquid acetylene or gas generated therefrom is absolutely prohibited.

Failure to observe these rules is as liable to endanger life as property.

To secure the largest measure of safety to life and property, the following rules for the installation of acetylene gas machines must be observed.

Class A.--Stationary Automatic Apparatus.

1. FOUNDATIONS.--(a) Must, where practicable, be of brick, stone, concrete or iron. If necessarily of wood they shall be extra heavy, located in a dry place and open to the circulation of air.

The ordinary board platform is not satisfactory. Wooden foundations shall be of heavy planking, joists or timbers, arranged so that the air will circulate around them so as to form a firm base.

(b) Must be so arranged that the machine will be level and unequal strain will not be placed on the generator or connexions.

2. LOCATION.--(a) Generators, especially in closely built up districts should preferably be placed outside of insured buildings in generator houses constructed and located in compliance with Rule 9.

(b) Generators must be so placed that the operating mechanism will have room for free and full play and can be adjusted without artificial light. They must not be subject to interference by children or careless persons, and if for this purpose further enclosure is necessary, it must be furnished by means of slatted partitions permitting the free circulation of air.

(c) Generators which from their construction are rendered inoperative during the process of recharging must be so located that they can be recharged without the aid of artificial light.

(d) Generators must be placed where water will not freeze.

3. ESCAPES OR RELIEF-PIPES.--Each generator must be provided with an escape or relief-pipe of ample size; no such pipe to be less than 3/4- inch internal diameter. This pipe shall be substantially installed, without traps, and so that any condensation will drain back to the generator. It must be carried to a suitable point outside the building, and terminate in an approved hood located at least 12 feet above ground and remote from windows.

The hood must be constructed in such a manner that it cannot be obstructed by rain, snow, ice, insects or birds.

4. CAPACITY.--(a) Must be sufficient to furnish gas continuously for the maximum lighting period to all lights installed. A lighting period of at least 5 hours shall be provided for in every case.

(b) Generators for conditions of service requiring lighting period of more than 5 hours must be of sufficient capacity to avoid recharging at night. The following ratings will usually be found advisable.

(i) For dwellings, and where machines are always used intermittently, the generator must have a rated capacity equal to the total number of burners installed.

(ii) For stores, opera houses, theatres, day-run factories, and similar service, the generator must have a rated capacity of from 30 to 50 per cent, in excess of the total number of burners installed.

(iii) For saloons and all night or continued service, the generator must have a rated capacity of from 100 to 200 per cent. in excess of the total number of burners installed.

(c) A small generator must never be installed to supply a large number of lights, even though it seems probable that only a few lights will be used at a time. An overworked generator adds to the cost of producing acetylene gas.

5. CARBIDE CHARGES.--Must be sufficient to furnish gas continuously for the maximum lighting period to all burners installed. In determining charges lump carbide must be estimated as capable of producing 4-1/2 cubic foot of gas to the pound, commercial 1/4-inch carbide 4 cubic feet of gas to the pound, and burners must be considered as requiring at least 25 per cent. more than their rated consumption of gas.

6. BURNERS.--Burners consuming one-half of a cubic foot of gas per hour are considered standard in rating generators. Those having a greater or less capacity will decrease or increase the number of burners allowable in proportion.

Burners usually consume from 25 to 100 per cent. more than their rated consumption of gas, depending largely on the working pressure. The so- called 1/2-foot burner when operated at pressures of from 20- to 25- tenths inches water column (2 to 2-1/2 inches) is usually used with best economy.

7. PIPING.--(a) Connexions from generators to service-pipes must be made with right and left thread nipples or long thread nipples with lock nuts. All forms of unions are prohibited.

(b) Piping must, as far as possible, be arranged so that any moisture will drain back to the generator. If low points occur of necessity in any piping, they must be drained through tees into drip cups permanently closed with screw caps or plugs. No pet-cocks shall be used.

(c) A valve and by-pass connexion must be provided from the service-pipe to the blow-off for removing the gas from the holder in case it should be necessary to do so.

(d) The schedule of pipe sizes for piping from generators to burners should conform to that commonly used for ordinary gas, but in no case must the feeders be smaller than three-eighths inch.

The following schedule is advocated:

3/8 inch pipe, 26 feet, three burners. 1/2 inch pipe, 30 feet, six burners. 3/4 inch pipe, 50 feet, twenty burners. 1 inch pipe, 70 feet, thirty-five burners. 1-1/4 inch pipe, 100 feet, sixty burners. 1-1/2 inch pipe, 150 feet, one hundred burners. 2 inch pipe, 200 feet, two hundred burners. 2-1/2 inch pipe, 300 feet, three hundred burners. 3 inch pipe, 450 feet, four hundred and fifty burners, 3-1/2 inch pipe, 500 feet, six hundred burners. 4 inch pipe, 600 feet, seven hundred and fifty burners.

(e) Machines of the carbide-feed type must not be fitted with continuous drain connexions leading to sewers, but must discharge into suitable open receptacles which may have such connections.

(f) Piping must be thoroughly tested both before and after the burners have been installed. It must not show loss in excess of 2 inches within twelve hours when subjected to a pressure equal to that of 15 inches of mercury.

(g) Piping and connexions must be installed by persons experienced in the installation of acetylene apparatus.

8. CARE AND ATTENDANCE.--In the care of generators designed for a lighting period of more than five hours always clean and recharge the generating chambers at regular stated intervals, regardless of the number of burners actually used.

Where generators are not used throughout the entire year always remove all water and gas and clean thoroughly at the end of the season during which they are in service.

It is usually necessary to take the bell portion out and invert it so as to allow all gas to escape. This should never be done in the presence of artificial light or fire of any kind.

Always observe a regular time, during daylight hours only, for attending to and charging the apparatus.

In charging the generating chambers of water-feed machines clean all residuum carefully from the containers and remove it at once from the building. Separate from the mass any unslacked carbide remaining and return it to the containers, adding now carbide as required. Be careful never to fill the containers over the specified mark, as it is important to allow for the swelling of the carbide when it comes in contact with water. The proper action and economy of the machine are dependent on the arrangement and amount of carbide placed in the generator. Carefully guard against the escape of gas.

Whenever recharging with carbide always replenish the water-supply.

Never deposit residuum or exhausted material from water-feed machines in sewer-pipes or near inflammable material.

Always keep water-tanks and water-seals filled with clean water.

Never test the generator or piping for leaks with a flame, and never apply flame to an outlet from which the burner has been removed.

Never use a lighted match, lamp, candle, lantern or any open light near the machine.

Failure to observe the above cautions is as liable to endanger life as property.

9. OUTSIDE GENERATOR HOUSES.--(a) Outside generator houses should not be located within 5 feet of any opening into, nor shall they open toward any adjacent building, and must be kept under lock and key.

(b) The dimensions must be no greater than the apparatus requires to allow convenient room for recharging and inspection of parts. The floor must be at least 12 inches above grade and the entire structure thoroughly weather-proof.

(c) Generator houses must be thoroughly ventilated, and any artificial heating necessary to prevent freezing shall be done by steam or hot-water systems.

(d) Generator houses must not be used for the storage of calcium carbide except in accordance with the rules relating to that subject (vide Chapter II.).

Class B.--Stationary Non-Automatic Apparatus.

10. FOUNDATIONS.--(a) Must be of brick, stone or concrete.

(b) Must be so arranged that the machine will be level and so that strain will not be brought upon the connexions.

11. GAS-HOUSES.--(a) Must be constructed entirely of non- combustible material and must not be lighted by any system of illumination involving open flames.

(b) Must be heated, where artificial heating is necessary to prevent freezing, by steam or hot-water systems, the heater to be located in a separate building, and no open flames to be permitted within generator enclosures.

(d) Must be provided with a permanent and effective system of ventilation which will be operative at all times, regardless of the periods of operation of the plant.

12. ESCAPE-PIPES.--Each generator must be provided with a vent-pipe of ample size, substantially installed, without traps. It must be carried to a suitable point outside the building and terminate in an approved hood located at least 12 feet above ground and remote from windows.

The hood must be constructed in such a manner that it cannot be obstructed by rain, snow, ice, insects or birds.

13. CARE AND MAINTENANCE.--All charging and cleaning of apparatus, generation of gas and execution of repairs must be done during daylight hours only, and generators must not be manipulated or in any way tampered with in the presence of artificial light.

This will require gasholders of a capacity sufficient to supply all lights installed for the maximum lighting period, without the necessity of generation of gas at night or by artificial light.

In the operation of generators of the carbide-feed type it is important that only a limited amount of carbide be fed into a given body of water. An allowance of at least one gallon of generating water per pound of carbide must be made in every case, and when this limit has been reached the generator should be drained and flushed, and clean water introduced. These precautions are necessary to avoid over-heating during generation and accumulation of hard deposits of residuum in the generating chamber.

(Rule 14, referring to the storage of carbide, has been quoted in Chapter II. (page 19)).

RULES FOR THE CONSTRUCTION OF GENERATORS.

The following Rules are intended to provide only against the more hazardous defects usually noted in apparatus of this kind. The Rules do not cover all details of construction nor the proper proportioning of parts, and devices which comply with these requirements alone are not necessarily suitable for listing as permissible for use. These points are often only developed in the examination required before permission is given for installation.

Class A.--Stationary Apparatus for Isolated Installations.

15. GENERAL RULES. GENERATORS.--(a) Must be made of iron or steel, and in a manner and of material to insure stability and durability.

(b) Must be automatically regulated and uniform in their action, producing gas only as immediate consumption demands, and so designed that gas is generated without producing sufficient heat to cause yellow discoloration of residuum (which will occur at about 500° F.) or abnormal pressure at any stage of the process when using carbide of any degree of fineness.

The presence of excessive heat tends to change the chemical character of the gas and may even cause its ignition, while in machines of the carbide-feed type, finely divided carbide will produce excessive pressure unless provision is made to guard against it.

(c) Must be so arranged that during recharging, back flow of gas from the gasholder will be automatically prevented, or so arranged that it will be impossible to charge the apparatus without first closing the supply-pipe to the gasholder, and to the other generating chambers if several are used.

This is intended to prevent the dangerous escape of gas.

(d) The water or carbide supply to the generating chamber must be so arranged that gas will be generated long enough in advance of the exhaustion of the supply already in the gasholder to allow the using of all lights without exhausting such supply.

This provides for the continuous working of the apparatus under all conditions of water-feed and carbide charge, and it obviates the extinction of lights through intermittent action of the machine.

(e) No valves or pet-cocks opening into the room from the gas- holding part or parts, the draining of which will allow an escape of gas, are permitted, and condensation from all parts of the apparatus must be automatically removed without the use of valves or mechanical working parts.

Such valves and pet-cocks are not essential; their presence increases the possibility of leakage. The automatic removal of condensation from the apparatus is essential to the safe working of the machine.

U-traps opening into the room from the gas-holding parts must not be used for removal of condensation. All sealed drip connexions must be so arranged as to discharge gas to the blow-off when blown out, and the seals must be self-restoring upon relief of abnormal pressure.

(f) The apparatus must be capable of withstanding fire from outside causes.

Sheet-metal joints must be double-seamed or riveted and thoroughly sweated with solder. Pipes must be attached to sheet-metal with lock-nuts or riveted flanges.

This prohibits the use of wood or of joints relying entirely upon solder.

(g) Gauge glasses, the breakage of which would allow the escape of gas, must not be used.

(h) The use of mercury seals is prohibited.

Mercury has been found unreliable as a seal in acetylene apparatus.(i) Combustible oils must not be used in connexion with the apparatus.

(j) The construction must be such that liquid seals shall not become thickened by the deposit of lime or other foreign matter.

(k) The apparatus must be constructed so that accidental siphoning of water will be impossible.

(l) Flexible tubing, swing joints, unions, springs, mechanical check-valves, chains, pulleys, stuffing-boxes and lead or fusible piping must not be used on acetylene apparatus except where failure of such parts will not vitally affect the working or safety of the machine.

Floats must not be used excepting in cases where failure will result only in rendering the machine inoperative.

(m) Every machine must be plainly marked with the maximum number of lights it is designed to supply, the amount of carbide necessary for a single charge, the manufacturer's name and the name of the machine.

16. GENERATING CHAMBERS.--(a) Must be constructed of galvanised iron or steel not less than No. 24 U.S. Standard gauge in thickness for capacities up to and including 20 gallons, not less than No. 22 U.S. Standard gauge for capacities between 20 and 75 gallons, and not less than No. 20 U.S. Standard gauge for capacities in excess of 75 gallons.

(b) Must each be connected with the gasholder in such a manner that they will, at all times, give open connexion either to the gasholder or to the blow-off pipe to the outer air.

This prevents dangerous pressure within or the escape of gas from the generating chamber.

(c) Must be so constructed that not more than 5 pounds of carbide can be acted upon at once, in machines which apply water in small quantities to the carbide.

This tends to reduce the danger of overheating and excessive after- generation by providing for division of the carbide charges in machines of this type.

(d) Must be provided with covers having secure fastenings to hold them properly in place and those relying on a water-seal must be submerged in at least 12 inches of water. Water-seal chambers for covers depending on a water-seal must be 1-1/2 inches wide and 15 inches deep, excepting those depending upon the filling of the seal chambers for the generation of gas, where 9 inches will be sufficient.

(e) Must be so designed that the residuum will not clog or affect the working of the machine and can conveniently be handled and removed.

(f) Must be provided with suitable vent connexions to the blow-off pipe so that residuum may be removed and the generating water replaced without causing siphoning or introducing air to the gasholder upon recharging.

This applies to machines of the carbide-feed type.

(g) Feed mechanism for machines of the carbide-feed type must be so designed that the direct fall of carbide from the carbide holder into the water of the generator is prevented at all positions of the feed mechanisms; or, when actuated by the rise and fall of a gas-bell, must be so arranged that the feed-valve will not remain open after the landing of the bell, and so that the feed valve remains inoperative as long as the filling opening on the carbide hopper remains open. Feed mechanisms must always be far enough above the water-level to prevent clogging from the accumulation of damp lime. For this purpose the distance should be not less than 10 inches.

17. CARBIDE CHAMBERS.--(a) Must be constructed of galvanised iron or steel not less than No. 24 U.S. Standard gauge in thickness for capacities up to and including 50 pounds and not less than No. 22 U.S. Standard gauge for capacities in excess of 50 pounds.

(b) Must have sufficient carbide capacity to supply the full number of burners continuously and automatically during the maximum lighting period.

This rule removes the necessity of recharging or attending to the machine at improper hours. Burners almost invariably require more than their rated consumption of gas, and carbide is not of staple purity, and there should therefore be an assurance of sufficient quantity to last as long as light is needed. Another important consideration is that in some establishments burners are called upon for a much longer period of lighting than in others, requiring a generator of greater gas-producing capacity. Machines having several generating chambers must automatically begin generation in each upon exhaustion of the preceding chamber.

18. GASHOLDERS.--(a) Must be constructed of galvanised iron or steel not less than No. 24 U.S. Standard gauge in thickness for capacities up to and including 20 gallons, not less than No. 22 U.S. Standard gauge for capacities between 20 and 75 gallons, and not less than No. 20 U.S. Standard gauge for capacities in excess of 75 gallons.

Gas-bells, if used, may be two gauges lighter than holders.

Condensation chambers, if placed under holders, to be of same gauge as holders.

(b) Must be of sufficient capacity to contain all gas generated after all lights have been extinguished.

If the holder is too small and blows off frequently after the lights are extinguished there is a waste of gas. This may suggest improper working of the apparatus and encourage tampering.

(c) Must, when constructed on the gasometer principle, be so arranged that when the gas-bell is filled to its maximum with gas at normal pressure its lip or lower edge will extend at least 9 inches below the inner water-level.

(d) Must, when constructed on the gasometer principle, have the dimensions of the tank portion so related to those of the bell that a pressure of at least 11 inches will be necessary before gas can be forced from the holder.

(e) The bell portion of a gasholder constructed on the gasometer principle must be provided with a substantial guide to its upward movement, preferably in the centre of the holder, carrying a stop acting to chock the bell 1 inch above the normal blow-off point.

This tends to insure the proper action of the bell and decreases the liability of escaping gas.

(f) A space of at least three-quarters of an inch must be allowed between the sides of the tank and the bell.

(g) All water-seals must be so arranged that the water-level may be readily seen and maintained.

19. WATER-SUPPLY.--(a) The supply of water to the generator for generating purposes must not be taken from the water-seal of any gasholder constructed on the gasometer principle, unless the feed mechanism is so arranged that the water-seals provided for in Rules 18, (c), (d), and (e) may be retained under all conditions. This provides for the proper level of water in the gasholder.

(b) In cases where machines of the carbide-feed type are supplied with water from city water-mains or house-pipes, the pipe connexion must discharge into the regularly provided filling trap on the generator and not through a separate continuous connexion leading into the generating chamber.

This is to prevent the expulsion of explosive mixtures through the filling trap in refilling.

20. RELIEFS OR SAFETY BLOW-OFFS.--(a) Must in all cases be provided, and must afford free vent to the outer air for any over- production of gas, and also afford relief in case of abnormal pressure in the machine.

Both the above-mentioned vents may be connected, with the same escape- pipe.

(b) Must be of at least 3/4-inch internal diameter and be provided with suitable means for connecting to the pipe loading outside of the building.

(d) Apparatus requiring pressure regulators must be provided with an additional approved safety blow-off attachment located between the pressure regulator and the service-pipes and discharging to the outer air.

This is intended to prevent the possibility of undue pressure in the service-pipes due to failure of the pressure regulator.

21. PRESSURES.--(a) The working pressure at the generator must not vary more than ten-tenths (1) inch water column under all conditions of carbide charge and feed, and between the limits of no load and 50 per cent. overload.

(b) Apparatus not requiring pressure regulators must be so arranged that the gas pressure cannot exceed sixty-tenths (6) inches water column.

This requires the use of the pressure relief provided for in Rule No. 20 (a).

(c) Apparatus requiring pressure regulators must be so arranged that the gas pressure cannot exceed three pounds to the square inch.

The pressure limit of 3 pounds is taken since that is the pressure corresponding to a water column about 6 feet high, which is about, the limit in point of convenience for water-sealed reliefs.

22. AIR MIXTURES.--Generators must be so arranged as to contain the minimum amount of air when first started or recharged, and no device or attachment facilitating or permitting mixture of air with the gas prior to consumption, except at the burners, shall be allowed.

Owing to the explosive properties of acetylene mixed with air, machines must be so designed that such mixtures are impossible.

23. PURIFIERS.--(a) Must be constructed of galvanised iron or steel not less than No. 24 U.S. Standard gauge in thickness.

(b) Where installed, purifiers must conform to the general rules for the construction of other acetylene apparatus and allow the free passage of gas.

(d) Purifiers must be located inside of gasholders, or, where necessarily outside, must have no hand-holes which can be opened without first shutting off the gas-supply.

24. PRESSURE REGULATORS.--(a) Must conform to the rules for the construction of other acetylene apparatus so far as they apply and must not be subject to sticking or clogging.

(b) Must be capable of maintaining a uniform pressure, not varying more than four-tenths inch water column, at any load within their rating.

Class B.--Stationary Apparatus for Central Station Service.

Generators of over 300 lights capacity for central station service are not required to be automatic in operation. Generators of less than 300 lights capacity must be automatic in operation and must comply in every respect with the requirements of Class A.

25. GENERAL RULES. GENERATORS.--(a) Must be substantially constructed of iron or steel and be protected against depreciation by an effective and durable preventive of corrosion.

Galvanising is strongly recommended as a protection against oxidation, and it may to advantage be reinforced by a thorough coating of asphaltum or similar material.

(b) Must contain no copper or alloy of copper in contact with acetylene, excepting in valves.

(c) Must be so arranged that generation will take place without overheating; temperatures in excess of 500° F. to be considered excessive.

(d) Must be provided with means for automatic removal of condensation from gas passages.

(e) Must be provided with suitable protection against freezing of any water contained in the apparatus.

No salt or other corrosive chemical is permissible as a protection against freezing.

(f) Must in general comply with the requirements governing the construction of apparatus for isolated installations so far as they are applicable.

(g) Must be so arranged as to insure correct procedure in recharging and cleaning.

(h) Generators of the carbide-feed type must be provided with some form of approved measuring device to enable the attendant to determine when the maximum allowable quantity of carbide has been fed into the generating chamber.

In the operation of generators of this type an allowance of at least 1 gallon of clean generating water per pound of carbide should be made, and the generator should be cleaned after slaking of every full charge. Where lump carbide is used the lumps may become embedded in the residuum, if the latter is allowed to accumulate at the bottom of the generating chamber, causing overheating from slow and restricted generation, and rendering the mass more liable to form a hard deposit and bring severe stresses upon the walls of the generator by slow expansion.

26. GENERATING CHAMBERS.--(a) Must each be connected with the gasholder in such a manner that they will, at all times, give open connexion either to the gasholder or to the blow-off pipe into the outer air.

(b) Must be so arranged as to guard against appreciable escape of gas to the room at any time during the introduction of the charges.

(c) Must be so designed that the residuum will not clog or affect the operation of the machine and can conveniently be handled and removed.

(d) Must be so arranged that during the process of cleaning and recharging the back-flow of gas from the gasholder or other generating chambers will be automatically prevented.

27. GASHOLDERS.--(a) Must be of sufficient capacity to contain at least 4 cubic feet of gas per 1/2-foot burner of the rating. This is to provide for the requisite lighting period without the necessity of making gas at night, allowance being made for the enlargement of burners caused by the use of cleaners.

(b) Must be provided with suitable guides to direct the movement of the bell throughout its entire travel.

28. PRESSURE RELIEFS.--Must in all cases be provided, and must be so arranged as to prevent pressure in excess of 100-tenths (10) inches water column in the mains.

29. PRESSURES.--Gasholders must be adjusted to maintain a pressure of approximately 25-tenths (2.5) inches water column in the mains.