Chapter XIV: Valuation and Analysis of Carbide

The sale and purchase of calcium carbide in this country will, under existing conditions, usually be conducted in conformity with the set of regulations issued by the British Acetylene Association, of which a copy, revised to date, is given below:

"REGULATIONS AS TO CARBIDE OF CALCIUM."

1. The carbide shall be guaranteed by the seller to yield, when broken to standard size, _i.e._, in lumps varying from 1 to 2-1/2 inches or larger, not less than 4.8 cubic feet per lb., at a barometric pressure of 30 inches and temperature of 60° Fahr. (15.55° Centigrade). The actual gas yield shall be deemed to be the gas yield ascertained by the analyst, plus 5 per cent.

"Carbide yielding less than 4.8 cubic feet in the sizes given above shall be paid for in proportion to the gas yield, _i.e._, the price to be paid shall bear the same relation to the contract price as the gas yield bears to 4.8 cubic feet per lb.

"2. The customer shall have the right to refuse to take carbide yielding in the sizes mentioned above less than 4.2 cubic foot, per lb., and it shall lie, in case of refusal and as from the date of the result, of the analysis being made known to either party, at the risk and expense of the seller.

"3. The carbide shall not contain higher figures of impurities than shall from time to time be fixed by the Association.

"4. No guarantee shall be given for lots of less than 3 cwt., or for carbide crushed to smaller than the above sizes.

"5. In case of dispute as to quality, either the buyer or the seller shall have the right to have one unopened drum per ton of carbide, or part of a ton, sent for examination to one of the analysts appointed by the Association, and the result of the examination shall be held to apply to the whole of the consignment to which the drum belonged. "6. A latitude of 5 per cent, shall be allowed for analysis; consequently differences of 5 per cent. above or below the yields mentioned in 1 and 2 shall not be taken into consideration.

"7. Should the yield of gas be less than 4.8 cubic feet less 5 per cent., the carriage of the carbide to and from the place of analysis and the cost of the analysis shall be paid for by the seller. Should the yield be more than 4.8 cubic feet less 5 per cent., the carriage and costs of analysis shall be borne by the buyer, who, in addition, shall pay an increase of price for the carbide proportionate to the gas yield above 4.8 cubic feet plus 5 per cent.

"8. Carbide of 1 inch mesh and above shall not contain more than 5 per cent. of dust, such dust to be defined as carbide capable of passing through a mesh of one-sixteenth of an inch.

"9. The seller shall not be responsible for deterioration of quality caused by railway carriage in the United Kingdom, unless he has sold including carriage to the destination indicated by the buyer.

"10. Carbide destined for export shall, in case the buyer desires to have it tested, be sampled at the port of shipment, and the guarantee shall cease after shipment.

"11. The analyst shall take a sample of not less than 1 lb. each from the top, centre, and bottom of the drum. The carbide shall be carefully broken up into small pieces, due care being taken to avoid exposure to the air as much as possible, carefully screened and tested for gas yield by decomposing it in water, previously thoroughly saturated by exposure to acetylene for a period of not less than 48 hours.

"12. Carbide which, when properly decomposed, yields acetylene containing from all phosphorus compounds therein more than .05 per cent. by volume of phosphoretted hydrogen, may be refused by the buyer, and any carbide found to contain more than this figure, with a latitude of .01 per cent. for the analysis, shall lie at the risk and expense of the seller in the manner described in paragraph 2.

"The rules mentioned in paragraph 7 shall apply as regards the carriage and costs of analysis; in other words, the buyer shall pay these costs if the figure is below 0.05 per cent. plus 0.01 per cent., and the seller if the figure is above 0.05 per cent. plus 0.01 per cent.

"The sampling shall take place in the manner prescribed in paragraphs 5 and 11, and the analytical examination shall be effected in the manner prescribed by the Association and obtainable upon application to the Secretary."

* * * * *

The following is a translation of the corresponding rules issued by the German Acetylene Association (_Der Deutsche Acetylenverein_) in regard to business dealings in calcium carbide, as put into force on April 1, 1909:

"REGULATIONS OF THE GERMAN ACETYLENE ASSOCIATION FOR TRADE IN CARBIDE.

"_Price_.

"The price is to be fixed per 100 kilogrammes (= 220 lb.) net weight of carbide in packages containing about 100 kilogrammes.

"By packages containing about 100 kilogrammes are meant packages containing within 10 per cent. above or below that weight.

"The carbide shall be packed in gas- and water-tight vessels of sheet- iron of the strength indicated in the prescriptions of the carrying companies.

"The prices for other descriptions of packing must be specially stated.

"_Place of Delivery_.

"For consignment for export, the last European shipping port shall be taken as the place of delivery.

"_Quality_.

"Commercial carbide shall be of such quality that in the usual lumps of 15 to 80 mm. (about 3/5 to 3 inches) diameter it shall afford a yield of at least 300 litres at 15° C. and 760 mm. pressure of crude acetylene per kilogramme for each consignment (= 4.81 cubic feet at 60° F. and 30 inches per lb.). A margin of 2 per cent. shall be allowed for the analysis. Carbide which yields less than 300 litres per kilogramme, but not less than 270 litres (= 4.33 cubic feet) of crude acetylene per kilogramme (with the above-stated 2 per cent. margin for analysis) must be accepted by the buyer. The latter, however, is entitled to make a proportionate deduction from the price and also to deduct the increased freight charges to the destination or, if the latter is not settled at the time when the transaction is completed, to the place of delivery. Carbide which yields less than 270 litres of crude acetylene per kilogramme need not be accepted.

"Carbide must not contain more than 5 per cent. of dust. By dust is to be understood all which passes through a screen of 1 mm. (0.04 inch) square, clear size of holes.

"Small carbide of from 4 to 15 mm. (= 1/6 to 3/5 inch) in size (and intermediate sizes) must yield on the average for each delivery at least 270 litres at 15° C. and 760 mm. pressure of crude acetylene per kilogramme (= 4.33 cubic feet at 60° F. and 30 inches per lb.) A margin of 2 per cent. shall be allowed for the analysis. Small carbide of from 4 to 15 mm. in size (and intermediate sizes) which yields less than 270 litres but not less than 250 litres (= 4.01 cubic feet per lb.) of crude acetylene per kilogramme (with the above-stated 2 per cent. margin for analysis) must be accepted by the buyer. The latter, however, is entitled to make a proportionate deduction from the price and also to deduct the increased freight charges to the destination or, if the latter is not settled at the time when the transaction is completed, to the place of delivery. Small carbide of from 4 to 15 mm. in size (and intermediate sizes) which yields less than 250 litres per kilogramme need not be accepted.

"Carbide shall only be considered fit for delivery if the proportion of phosphoretted hydrogen in the crude acetylene does not amount to more than 0.04 volume per cent. A margin of 0.01 volume per cent. shall be allowed for the analysis for phosphoretted hydrogen. The whole of the phosphorus compounds contained in the gas are to be calculated as phosphoretted hydrogen.

"_Period for Complaints._

"An interval of four weeks from delivery shall be allowed for complaints for consignments of 5000 kilogrammes (= 5 tons) and over, and an interval of two weeks for smaller consignments. A complaint shall refer only to a quantity of carbide remaining at the time of taking the sample.

"_Determination of Quality._

"1. In case the parties do not agree that the consignee is to send to the analyst for the determination of the quality one unopened and undamaged drum when the consignment is less than 5000 kilogrammes, and two such drums when it is over 5000 kilogrammes, a sample for the purpose of testing the quality is to be taken in the following manner:

"A sample having a total weight of at least 2 kilogrammes (= 4.4 lb.) is to be taken. If the delivery to be tested does not comprise more than ten drums, the sample is to be taken from an unopened and undamaged drum selected at random. With deliveries of more than ten drums, the sample is to be drawn from not fewer than 10 per cent, of the lot, and from each of the unopened and undamaged drums drawn for the purpose not less than 1 kilogramme (= 2.2 lb.) is to be taken.

"The sampling is to be carried out by a trustworthy person appointed by the two parties, or by one of the experts regularly recognised by the German Acetylene Association, thus: Each selected drum, before opening, is to be turned over twice (to got rid of any local accumulation of dust) and the requisite quantity is to be withdrawn with a shovel (not with the hand) from any part of it. These samples are immediately shot into one or more vessels which are closed air- and water-tight. The lid is secured by a seal. No other description of package, such as cardboard cases, boxes, &c., is permissible.

"If there is disagreement as to the choice of a trustworthy person, each of the two parties is to take the required quantity, as specified above.

"2. The yield of gas and the proportion of phosphoretted hydrogen contained in it are to be determined by the methods prescribed by the German Acetylene Association. If there are different analyses giving non- concordant results, an analysis is to be made by the German Acetylene Association, which shall be accepted as final and binding.

"In cases, however, where the first analysis has been made in the Laboratory of the German Acetylene Association and arbitration is required, the decisive analysis shall be made by the Austrian Acetylene Association. If one of the parties prevents the arbitrator's analysis being carried out, the analysis of the other party shall be absolutely binding on him.

"3. The whole of the cost of sampling and analysis is to be borne by the party in the wrong."

* * * * *

The corresponding regulations issued by the Austrian Acetylene Association (_Der Oesterreichische Acetylenverein_) are almost identical with those of the German Association. They contain, however, provisions that the price is to include packing, that the carbide must not be delivered in lumps larger than the fist, that the sample may be sealed in a glass vessel with well-ground glass stopper, that the sample is to be transmitted to the testing laboratory with particulars of the size of the lots and the number of drums drawn for sampling, and that the whole of it is to be gasified in lots of upwards of 1 kilogramme (= 2.2 lb.) apiece.

In Italy, it is enacted by the Board of Agriculture, Commerce and Industry that by calcium carbide is to be understood for legal purposes also any other carbide, or carbide-containing mixture, which evolves acetylene by interaction with water. Also that only calcium carbide, which on admixture with water yields acetylene containing less than 1 per cent. of its volume of sulphuretted hydrogen and phosphoretted hydrogen taken together, may be put on the market.

It is evident from the regulations quoted that the determination of the volume of gas which a particular sample of calcium carbide is capable of yielding, when a given weight of it is decomposed under the most favourable conditions, is a matter of the utmost practical importance to all interested in the trafficking of carbide, _i.e._, to the makers, vendors, brokers, and purchasers of that material, as well as to all makers and users of acetylene generating plant. The regulations of the British Association do not, however, give details of the method which the analyst should pursue in determining the yield of acetylene; and while this may to a certain extent be advantageously left to the discretion of the competent analyst, it is desirable that the results of the experience already won by those who have had special opportunities for practising this branch of analytical work should be embodied in a set of directions for the analysis of carbide, which may be followed in all ordinary analyses of that material. By the adoption of such a set of directions as a provisional standard method, disputes as to the quantity of carbide will be avoided, while it will still be open to the competent analyst to modify the method of procedure to meet the requirements of special cases. It would certainly be unadvisable in the present state of our analytical methods to accept any hard and fast of rules for analysis for determining the quality of carbide, but it is nevertheless well to have the best of existing methods codified for the guidance of analysts. The substance of the directions issued by the German Association (_Der Deutsche Acetylenverein_) is reproduced below.

"METHODS FOR THE DETERMINATION OF TILE YIELD OF GAS FROM CALCIUM CARBIDE.

"The greatest precision is attained when the whole of the sample submitted to the analyst is gasified in a carbide-to-water apparatus, and the gas evolved is measured in an accurately graduated gasholder.

"The apparatus used for this analysis must not only admit of all the precautionary rules of gas-analytical work being observed, but must also fulfil certain other experimental conditions incidental to the nature of the analysis.

"(_a_) The apparatus must be provided with an accurate thermometer to show the temperature of the confining water, and with a pressure gauge, which is in communication with the gasholder.

"(_b_) The generator must either be provided with a gasholder which is capable of receiving the quantity of gas evolved from the whole amount of carbide, or the apparatus must be so constructed that it becomes possible with a gasholder which in not too large (up to 200 litres = say 7 cubic feet capacity) to gasify a larger amount of carbide.

"(_c_) The generator must be constructed so that escape of the evolved gas from it to the outer air is completely avoided.

"(_d_) The gasholder must be graduated in parts up to 1/4 per cent. of its capacity, must travel easily, and be kept, as far as may be in suspension by counterweighting.

"(_e_) The water used for decomposing the carbide and the confining water must be saturated, before use, with acetylene, and, further, the generator must, before the analysis proper, be put under the pressure of the confining (or sealing) liquid."

The following is a description of a typical form of apparatus corresponding with the foregoing requirements:

"The apparatus, shown in the annexed figure, consists of the generator A, the washer B, and the gasholder C.

"The generator A consists of a cylindrical vessel with sloping bottom, provided with a sludge outlet _a_, a gas exit-pipe _b_, and a lid _b'_ fastened by screws. In the upper part ten boxes _c_ are installed for the purpose of receiving the carbide. The bottoms of those boxes are flaps which rest through their wire projections on a revolvable disc _d_, which is mounted on a shaft _l_. This shaft passes through a stuffing-box to the outside of the generator and can be rotated by moans of the chains _f_, the pulleys _g_ and _h_, and the winch _i_. Its rotation causes rotation of the disc _d_. The disc _d_, on which the bottoms of the carbide- holders are supported, is provided with a slot _e_. On rotating the disc, on which the supporting wires of the bottoms of the carbide-holders rest, the slot is brought beneath these wires in succession; and the bottoms, being thus deprived of their support, drop down. It is possible in this way to effect the discharge of the several carbide-holders by gradual turning of the winch _i_.

"The washer B is provided with a thermometer _m_ passing through a sound stuffing-box and extending into the water.

"The gasholder C is provided with a scale and pointer, which indicate how much gas there is in it. It is connected with the pressure-gauge _n_, and is further provided with a control thermometer _o_. The gas exit-pipe _q_ can be shut off by a cock. There is a cock between the gasholder and the washer for isolating one from the other.

"The dimensions of the apparatus are such that each carbide-holder can contain readily about half a kilogramme (say l lb.) of carbide. The gasholder is of about 200 litres (say 7 cubic feet) capacity; and if the bell is 850 mm. (= 33-1/2 inches) high, and 550 mm. (= 21-1/2 inches) in diameter it will admit of the position being read off to within half a litre (say 0.02 cubic foot)."

The directions of the German Association for sampling a consignment of carbide packed in drums each containing 100 kilogrammes (say 2 cwt.) have already been given in the rules of that body. They differ somewhat from those issued by the British Association (_vide ante_), and have evidently been compiled with a view to the systematic and rapid sampling of larger consignments than are commonly dealt with in this country. Drawing a portion of the whole sample from every tenth drum is substantially the same as the British Association's regulations for cases of dispute, viz., to have one unopened drum (_i.e._, one or two cwt.) per ton of carbide placed at the analyst's disposal for sampling. Actually the mode of drawing a portion of the whole sample from every tenth vessel, or lot, where a large number is concerned, is one which would naturally be adopted by analysts accustomed to sampling any other products so packed or stored, and there in no reason why it should be departed from in the case of large consignments of carbide. For lots of less than ten drums, unless there is reason to suspect want of uniformity, it should usually suffice to draw the sample from one drum selected at random by the sampler. The analyst, or person who undertakes the sampling, must, however, exercise discretion as to the scheme of sampling to be followed, especially if want of uniformity of the several lots constituting the consignment in suspected. The size of the lumps constituting a sample will be referred to later.

The British Association's regulations lead to a sample weighing about 3 lb. being obtained from each drum. If only one drum is sampled, the quantity taken from each position may be increased with advantage so as to give a sample weighing about 10 lb., while if a large number of drums is sampled, the several samples should be well mixed, and the ordinary method of quartering and re-mixing followed until a representative portion weighing about 10 lb. remains.

A sample representative of the bulk of the consignment having been obtained, and hermetically sealed, the procedure of testing by means of the apparatus already described may be given from the German Association's directions:

"The first carbide receptacle is filled with 300 to 400 grammes (say 3/4 lb.) of any readily decomposable carbide, and is hung up in the apparatus in such a position with regard to the slot _e_ on the disc _d_ that it will be the first receptacle to be discharged when the winch _i_ is turned. The tin or bottle containing the sample for analysis is then opened and weighed on a balance capable of weighing exactly to 1/2 gramme (say 10 grains). The carbide in it is then distributed quickly, and as far as may be equally, into the nine remaining carbide receptacles, which are then shut and hung up quickly in the generator. The lid _b'_ is then screwed on the generator to close it, and the empty tin or bottle, from which the sample of carbide has been removed, is weighed.

"The contents of the first carbide receptacle are then discharged by turning the winch _i_. Their decomposition ensures on the one hand that the sealing water and the generating water are saturated with acetylene, and on the other hand that the dead space in the generator is brought under the pressure of the seal, so that troublesome corrections which would otherwise be entailed are avoided. After the carbide is completely decomposed, but not before two hours at least have elapsed, the cock _p_ is shut, and the gasholder is run down to the zero mark by opening the cock _q_. The cock _q_ is then shut, _p_ is opened, and the analytical examination proper is begun by discharging the several carbide receptacles by turning the winch _i_. After the first receptacle has been discharged, five or ten minutes are allowed to elapse for the main evolution of gas to occur, and the cock _p_ is then shut. Weights are added to the gasholder until the manometer _n_ gives the zero reading; the position of the gasholder C is then read off, and readings of the barometer and of the thermometer _o_ are made. The gasholder is then emptied down to the zero mark by closing the cock _p_ and opening _q_. When this is done _q_ is closed and _p_ is opened, and the winch _i_ is turned until the contents of the next carbide receptacle are discharged. This procedure is followed until the carbide from the last receptacle has been gasified; then, after waiting until all the carbide has been decomposed, but in any case not less than two hours, the position of the gasholder is read, and readings of the barometer and thermometer are again taken. The total of the values obtained represents the yield of gas from the sample examined."

The following example is quoted:

Weight of the tin received, with its contained |
carbide . . . . . ._| = 6325 grammes.
Weight of the empty tin . . . . = 1485 "
_______
Carbide used . . . = 4840 " = 10670 lb.

The carbide in question was distributed among the nine receptacles and gasified. The readings were:

________________________________________________ | | | | | | No. | Litres. | Degrees C. | Millimetres. | |______|__________|______________|_______________| | | | | | | 1 | 152.5 | 13 | 762 | | 2 | 136.6 | " | " | | 3 | 138.5 | " | " | | 4 | 161.0 | " | " | | 5 | 131.0 | " | " | | 6 | 182.5 | 13.5 | " | | 7 | 146.0 | " | " | | 8 | 163.0 | 14.0 | " | | 9 | 178.5 | " | " | |______|__________|______________|_______________|

After two hours, the total of the readings was 1395.0 litres at 13.5° C. and 762 mm., which is equivalent to 1403.7 litres (= 49.57 cubic feet) at 15° C. and 760 mm. (or 60° F. and 30 inches; there is no appreciable change of volume of a gas when the conditions under which it is measured are altered from 15° C. and 760 mm. to 60° F. and 30 inches, or _vice versâ_).

The yield of gas from this sample is therefore 1403.7/4.840 = 290 litres at 15° C. and 760 mm. per kilogramme, or 49.57/10.67 = 4.65 cubic feet at 60° F. and 30 inches per pound of carbide. The apparatus described can, of course, be used when smaller samples of carbide only are available for gasification, but the results will be less trustworthy if much smaller quantities than those named are taken for the test.

Other forms of carbide-to-water apparatus may of course be devised, which will equally well fulfil the requisite conditions for the test, viz., complete decomposition of the whole of the carbide without excessive rise of temperature, and no loss of gas by solution or otherwise.

An experimental wet gas-motor, of which the water-line has been accurately set (by means of the Gas Referees' 1/12 cubic foot measure, or a similar meter-proving apparatus), may be used in place of the graduated gasholder for measuring the volume of the gas evolved, provided the rate of flow of the gas does not exceed 1/6 cubic foot, or say 5 litres per minute. If the generation of gas is irregular, as when an apparatus of the type described above is used, it is advisable to insert a small gasholder or large bell-governor between the washer and the meter. The meter must be provided with a thermometer, according to the indications of which the observed volumes must be corrected to the corresponding volume at normal temperature.

If apparatus such as that described above is not available, fairly trustworthy results for practical purposes may be obtained by the decomposition of smaller samples in the manner described below, provided these samples are representative of the average composition of the larger sample or bulk, and a number of tests are made in succession and the results of individual tests do not differ by more than 10 litres of gas per kilogramme (or 0.16 cubic foot per pound) of carbide.

It is necessary at the outset to reduce large lumps of carbide in the sample to small pieces, and this must be done with as little exposure as possible to the (moist) air. Failing a good pulverising machine of the coffee-mill or similar type, which does its work quickly, the lumps must be broken as rapidly as possible in a dry iron mortar, which may with advantage be fitted with a leather or india-rubber cover, through a hole in which the pestle passes. As little actual dust as possible should be made during pulverisation. The decomposition of the carbide is best effected by dropping it into water and measuring the volume of gas evolved with the precautions usually practised in gas analysis. An example of one of the methods of procedure described by the German Association will show how this test can be satisfactorily carried out:

"A Woulff's bottle, _a_ in the annexed figure, of blown glass and holding about 1/4 litre is used as the generating vessel. One neck, about 15 mm. in internal diameter, is connected by flexible tubing with a globular vessel _b_, having two tubulures, and this vessel is further connected with a conical flask _c_, holding about 100 c.c. The other neck is provided with tubing _d_, serving to convey the gas to the inlet-tube, with tap _e_, of the 20-litre measuring vessel _f_, which is filled with water saturated with acetylene, and communicates through its lower tubulure with a similar large vessel _g_. The generating vessel _a_ is charged with about 150 c.c. of water saturated with acetylene. The vessel _f_ is filled up to the zero mark by raising the vessel _g_; the tap _e_ is then shut, and connexion is made with the tube _d_. Fifty grammes (or say 2 oz.) of the pulverised carbide are then weighed into the flask _c_ and this is connected by the flexible tubing with the vessel _b_. The carbide is then decomposed by bringing it in small portions at a time into the bulb _b_ by raising the flask _c_, and letting it drop from _b_ into the generating vessel _a_, after having opened the cock _e_ and slightly raised the vessel _f_. After the last of the carbide has been introduced two hours are allowed to elapse, and the volume of gas in _f_ is then read while the water stands at the same level in _f_ and _g_, the temperature and pressure being noted simultaneously."

A second, but less commendable method of decomposing the carbide is by putting it in a dry two-necked bottle, one neck of which is connected with _e_, and dropping water very slowly from a tap-funnel, which enters the other neck, on to the carbide. The generating bottle should be stood in water, in order to keep it cool, and the water should be dropped in at the rate of about 50 c.c. in one hour. It will take about three hours completely to gasify the 50 grammes of carbide under these conditions. The gas is measured as before.

Cedercreutz has carried out trials to show the difference between the yields found from large and small carbide taken from the same drum. One sample consisted of the dust and smalls up to about 3/5 inch in size, while the other contained large carbide as well as the small. The latter sample was broken to the same size as the former for the analysis. Tests were made both with a large testing apparatus, such as that shown in Fig. 22, and with a small laboratory apparatus, such as that shown in Fig. 23. The dust was screened off for the tests made in the large apparatus. Two sets of testings were made on different lots of carbide, distinguished below as "A" and "B," and about 80 grammes wore taken for each determination in the laboratory apparatus, and 500 grammes in the large apparatus. The results are stated in litres (at normal temperature and pressure) per kilogramme of carbide.

___________________________________________________________________ | | | | | | "A" | "B" | |_____________________________________________________|______|______| | | | | | Lot |Litres|Litres| | Small carbide, unscreened, in laboratory \ (1) | 276 | 267 | | apparatus . . . . . / (2) | 273 | 270 | | Average sample of carbide, unscreened, in \ (1) | 318 | 321 | | laboratory apparatus . . . / (2) | 320 | 321 | | Small carbide, dust freed, in large apparatus (1) | 288 | 274 | | Average sample of carbide, dust freed, in \ (2) | 320 | 322 | | large apparatus . . . . / | | | |_____________________________________________________|______|______|

As the result of the foregoing researches Cedercreutz has recommended that in order to sample the contents of a drum, they should be tipped out, and about a kilogramme (say 2 to 3 lb.) taken at once from them with a shovel, put on an iron base and broken with a hammer to pieces of about 2/5 inch, mixed, and the 500 grammes required for the analysis in the form of testing plant which he employs taken from this sample. Obviously a larger sample can be taken in the same manner. On the other hand the British and German Associations' directions for sampling the contents of a drum, which have already been quoted, differ somewhat from the above, and must generally be followed in cases of dispute.

Cedercreutz's figures, given in the above table, show that it would be very unfair to determine the gas-making capacity of a given parcel of carbide in which the lumps happened to vary considerably in size by analysing only the smalls, results so obtained being possibly 15 per cent. too low. This is due to two causes: first, however carefully it be stored, carbide deteriorates somewhat by the attack of atmospheric moisture; and since the superficies of a lump (where the attack occurs) is larger in proportion to the weight of the lump as the lump itself is smaller, small lumps deteriorate more on keeping than large ones. The second reason, however, is more important. Not being a pure chemical substance, the commercial material calcium carbide varies in hardness; and when it is merely crushed (not reduced altogether to powder) the softer portions tend to fall into smaller fragments than the hard portions. As the hard portions are different in composition from the soft portions, if a parcel is sampled by taking only the smalls, practically that sample contains an excess of the softer part of the original material, and as such is not representative. Originally the German Acetylene Association did not lay down any rules as to the crushing of samples by the analyst, but subsequently they specified that the material should be tested in the size (or sizes) in which it was received. The British Association, on the contrary, requires the sample to be broken in small pieces. If the original sample is taken in such fashion as to include large and small lumps as accurately as possible in the same proportion as that in which they occur in the main parcel, no error will be introduced if that sample is crushed to a uniform size, and then subdivided again; but a small deficiency in gas yield will be produced, which will be in the consumer's favour. It is not altogether easy to see the advantage of the British idea of crushing the sample over the German plan of leaving it alone; because the analytical generator will easily take, or its parts could be modified to take, the largest lumps met with. If the sample is in very large masses, and is decomposed too quickly, polymerisation of gas may be set up; but on the other hand, the crushing and re-sampling will cause wastage, especially in damp weather, or when the sampling has to be done in inconvenient places. The British Association requires the test to be made on carbide parcels ranging between 1 and 2-1/2 inches or larger, because that is the "standard" size for this country, and because no guarantee is to be had or expected from the makers as to the gas-producing capacity of smaller material. Manifestly, if a consumer employs such a form of generator that he is obliged to use carbide below "standard" size, analyses may be made on his behalf in the ordinary way; but he will have no redress if the yield of acetylene is less than the normal. This may appear a defect or grievance; but since in many ways the use of small carbide (except in portable lamps) is not advantageous--either technically or pecuniarily--the rule simply amounts to an additional judicious incentive to the adoption of apparatus capable of decomposing standard-sized lumps. The German and Austrian Associations' regulations, however, provide a standard for the quality of granulated carbide.

It has been pointed out that the German Association's direction that the water used in the testing should be saturated with acetylene by a preliminary decomposition of 1/2 kilogramme of carbide is not wholly adequate, and it has been suggested that the preliminary decomposition should be carried out twice with charges of carbide, each weighing not less than 1 per cent. of the weight of water used. A further possible source of error lies in the fact that the generating water is saturated at the prevailing temperature of the room, and liberates some of its dissolved acetylene when the temperature rises during the subsequent generation of gas. This error, of course, makes the yield from the sample appear higher than it actually is. Its effects may be compensated by allowing time for the water in the generator or gasholder to cool to its original temperature before the final reading is made.

With regard to the measurement of the temperature of the evolved gas in the bell gasholder, it is usual to assume that the reading of a thermometer which passes through the crown of the gasholder suffices. If the thermometer has a very long stem, so that the bulb is at about the mid-height of the filled bell, this plan is satisfactory, but if an ordinary thermometer is used, it is better to take, as the average temperature of the gas in the holder, the mean of the readings of the thermometer in the crown, and of one dipping into the water of the holder seal.

The following table gives factors for correcting volumes of gas observed at any temperature and pressure falling within its range to the normal temperature (60° F.) and normal barometric height (30 inches). The normal volume thus found is, as already stated, not appreciably different from the volume at 15° C. and 760 mm. (the normal conditions adopted by Continental gas chemists). To use the table, find the observed temperature and the observed reading of the barometer in the border of the table, and in the space where these vertical and horizontal columns meet will be found a number by which the observed volume of gas is to be multiplied in order to find the corresponding volume under normal conditions. For intermediate temperatures, &c., the factors may be readily inferred from the table by inspection. This table must only be applied when the gas is saturated with aqueous vapour, as is ordinarily the case, and therefore a drier must not be applied to the gas before measurement.

Hammerschmidt has calculated a similar table for the correction of volumes of gas measured at temperatures ranging from 0° to 30° C., and under pressures from 660 to 780 mm., to 15° C. and 760 mm. It is based on the coefficient of expansion of acetylene given in Chapter VI., but, as was there pointed out, this coefficient differs by so little from that of the permanent gases for which the annexed table was compiled, that no appreciable error results from the use of the latter for acetylene also. A table similar to the annexed but of more extended range is given in the "Notification of the Gas Referees," and in the text-book on "Gas Manufacture" by one of the authors.

The determination of the amounts of other gases in crude or purified acetylene is for the most part carried out by the methods in vogue for the analysis of coal-gas and other illuminating gases, or by slight modifications of them. For an account of these methods the textbook on "Gas Manufacture" by one of the authors may be consulted. For instance, two of the three principal impurities in acetylene, viz., ammonia and sulphuretted hydrogen, may be detected and estimated in that gas in the same manner as in coal gas. The detection and estimation of phosphine are, however, analytical operations peculiar to acetylene among common illuminating gases, and they must therefore be referred to.

_Table to facilitate the Correction of the Volume of Gas at different Temperatures and under different Atmospheric Pressures._

_____________________________________________________ | | | | | THERMOMETER. | | BAR.|_______________________________________________| | | | | | | | | | | 46° | 48° | 50° | 52° | 54° | 56° | |_____|_______|_______|_______|_______|_______|_______| | | | | | | | | |28.4 | 0.979 | 0.974 | 0.970 | 0.965 | 0.960 | 0.955 | |28.5 | 0.983 | 0.978 | 0.973 | 0.968 | 0.964 | 0.959 | |28.6 | 0.986 | 0.981 | 0.977 | 0.972 | 0.967 | 0.962 | |28.7 | 0.990 | 0.985 | 0.980 | 0.975 | 0.970 | 0.966 | |28.8 | 0.993 | 0.988 | 0.984 | 0.979 | 0.974 | 0.969 | |28.9 | 0.997 | 0.992 | 0.987 | 0.982 | 0.977 | 0.973 | |29.0 | 1.000 | 0.995 | 0.990 | 0.986 | 0.981 | 0.976 | |29.1 | 1.004 | 0.999 | 0.994 | 0.989 | 0.984 | 0.979 | |29.2 | 1.007 | 1.002 | 0.997 | 0.992 | 0.988 | 0.982 | |29.3 | 1.011 | 1.005 | 1.001 | 0.996 | 0.991 | 0.986 | |29.4 | 1.014 | 1.009 | 1.004 | 0.999 | 0.995 | 0.990 | |29.5 | 1.018 | 1.013 | 1.008 | 1.003 | 0.998 | 0.993 | |29.6 | 1.021 | 1.016 | 1.011 | 1.006 | 1.001 | 0.996 | |29.7 | 1.025 | 1.019 | 1.015 | 1.010 | 1.005 | 1.000 | |29.8 | 1.028 | 1.023 | 1.018 | 1.013 | 1.008 | 1.003 | |29.9 | 1.031 | 1.026 | 1.022 | 1.017 | 1.012 | 1.007 | |30.0 | 1.035 | 1.030 | 1.025 | 1.020 | 1.015 | 1.010 | |30.1 | 1.038 | 1.033 | 1.029 | 1.024 | 1.019 | 1.014 | |30.2 | 1.042 | 1.037 | 1.032 | 1.027 | 1.022 | 1.017 | |30.3 | 1.045 | 1.040 | 1.036 | 1.030 | 1.025 | 1.020 | |30.4 | 1.049 | 1.044 | 1.039 | 1.034 | 1.029 | 1.024 | |30.5 | 1.052 | 1.047 | 1.042 | 1.037 | 1.032 | 1.027 | |_____|_______|_______|_______|_______|_______|_______| _____________________________________________________ | | | | | THERMOMETER. | | BAR.|_______________________________________________| | | | | | | | | | | 58° | 60° | 62° | 64° | 66° | 68° | |_____|_______|_______|_______|_______|_______|_______| | | | | | | | | |28.5 | 0.954 | 0.949 | 0.944 | 0.939 | 0.934 | 0.929 | |28.6 | 0.958 | 0.953 | 0.947 | 0.943 | 0.938 | 0.932 | |28.7 | 0.961 | 0.956 | 0.951 | 0.946 | 0.941 | 0.936 | |28.8 | 0.964 | 0.959 | 0.954 | 0.949 | 0.944 | 0.939 | |28.9 | 0.968 | 0.963 | 0.958 | 0.953 | 0.948 | 0.942 | |29.0 | 0.971 | 0.966 | 0.961 | 0.956 | 0.951 | 0.946 | |29.1 | 0.975 | 0.969 | 0.964 | 0.959 | 0.954 | 0.949 | |29.2 | 0.978 | 0.973 | 0.968 | 0.963 | 0.958 | 0.952 | |29.3 | 0.981 | 0.976 | 0.971 | 0.966 | 0.961 | 0.956 | |29.4 | 0.985 | 0.980 | 0.975 | 0.969 | 0.964 | 0.959 | |29.5 | 0.988 | 0.983 | 0.978 | 0.973 | 0.968 | 0.962 | |29.6 | 0.992 | 0.986 | 0.981 | 0.976 | 0.971 | 0.966 | |29.7 | 0.995 | 0.990 | 0.985 | 0.980 | 0.974 | 0.969 | |29.8 | 0.998 | 0.993 | 0.988 | 0.983 | 0.978 | 0.972 | |29.9 | 1.002 | 0.997 | 0.991 | 0.986 | 0.981 | 0.976 | |30.0 | 1.005 | 1.000 | 0.995 | 0.990 | 0.985 | 0.979 | |30.1 | 1.009 | 1.003 | 0.998 | 0.993 | 0.988 | 0.983 | |30.2 | 1.012 | 1.007 | 1.002 | 0.996 | 0.991 | 0.986 | |30.3 | 1.015 | 1.010 | 1.005 | 1.000 | 0.995 | 0.989 | |30.4 | 1.019 | 1.014 | 1.008 | 1.003 | 0.998 | 0.993 | |30.5 | 1.022 | 1.017 | 1.012 | 1.006 | 1.001 | 0.996 | |_____|_______|_______|_______|_______|_______|_______| _____________________________________________ | | | | | THERMOMETER. | | BAR.|_______________________________________| | | | | | | | | | 70° | 72° | 74° | 76° | 78° | |_____|_______|_______|_______|_______|_______| | | | | | | | |28.4 | 0.921 | 0.915 | 0.910 | 0.905 | 0.900 | |28.5 | 0.924 | 0.919 | 0.914 | 0.908 | 0.903 | |28.6 | 0.927 | 0.922 | 0.917 | 0.912 | 0.906 | |28.7 | 0.931 | 0.925 | 0.920 | 0.915 | 0.909 | |28.8 | 0.934 | 0.929 | 0.924 | 0.918 | 0.913 | |28.9 | 0.937 | 0.932 | 0.927 | 0.921 | 0.916 | |29.0 | 0.941 | 0.935 | 0.930 | 0.925 | 0.919 | |29.1 | 0.944 | 0.939 | 0.933 | 0.928 | 0.923 | |29.2 | 0.947 | 0.942 | 0.937 | 0.931 | 0.926 | |29.3 | 0.950 | 0.945 | 0.940 | 0.935 | 0.929 | |29.4 | 0.954 | 0.949 | 0.943 | 0.938 | 0.932 | |29.5 | 0.957 | 0.952 | 0.947 | 0.941 | 0.936 | |29.6 | 0.960 | 0.955 | 0.950 | 0.944 | 0.939 | |29.7 | 0.964 | 0.959 | 0.953 | 0.948 | 0.942 | |29.8 | 0.967 | 0.962 | 0.957 | 0.951 | 0.946 | |29.9 | 0.970 | 0.965 | 0.960 | 0.954 | 0.949 | |30.0 | 0.974 | 0.968 | 0.963 | 0.958 | 0.952 | |30.1 | 0.977 | 0.972 | 0.966 | 0.961 | 0.955 | |30.2 | 0.980 | 0.975 | 0.970 | 0.964 | 0.959 | |30.3 | 0.984 | 0.978 | 0.973 | 0.968 | 0.962 | |30.4 | 0.987 | 0.982 | 0.976 | 0.971 | 0.965 | |30.5 | 0.990 | 0.985 | 0.980 | 0.974 | 0.969 | |_____|_______|_______|_______|_______|_______|

For the detection of phosphine, Bergé's solution may be used. It is a "solution of 8 to 10 parts of corrosive sublimate in 80 parts of water and 20 parts of 30 per cent. hydrochloric acid." It becomes cloudy when gas containing phosphine is passed into it. It is, however, applied most conveniently in the form of Keppeler's test-papers, which have been described in Chapter V. Test-papers for phosphine, the active body in which has not yet been divulged, have recently been produced for sale by F. B. Gatehouse.

The estimation of phosphine will usually require to be carried out either (1) on gas directly evolved from carbide in order to ascertain if the carbide in question yields an excessive proportion of phosphine, or (2) upon acetylene which is presumably purified, drawn either from the outlet of the purifier or from the service-pipes, with the object of ascertaining whether an adequate purification in regard to phosphine has been accomplished. In either case, the method of estimation is the same, but in the first, acetylene should be specially generated from a small representative sample of the carbide and led directly into the apparatus for the absorption of the phosphine. If the acetylene passes into the ordinary gasholder, the amount of phosphine in gas drawn off from the holder will vary from time to time according to the temperature and the degree of saturation of the water in the holder-tank with phosphine, as well as according to the amount of phosphine in the gas generated at the time.

A method frequently employed for the determination of phosphine in acetylene is one devised by Lunge and Cedercreutz. If the acetylene is to be evolved from a sample of carbide in order to ascertain how much phosphine the latter yields to the gas, about 50 to 70 grammes of the carbide, of the size of peas, are brought into a half-litre flask, and a tap-funnel, with the mouth of its stem contracted, is passed through a rubber plug fitting the mouth of the flask. A glass tube passing through the plug serves to convey the gas evolved to an absorption apparatus, which is charged with about 75 c.c. of a 2 to 3 per cent. solution of sodium hypochlorite. The absorption apparatus may be a ten-bulbed absorption tube or any convenient form of absorption bulbs which subject the gas to intimate contact with the solution. If acetylene from a service-pipe is to be tested, it is led direct from the nozzle of a gas- tap to the absorption tube, the outlet of which is connected with an aspirator or the inlet of an experimental meter, by which the volume of gas passed through the solution is measured. But if the generating flask is employed, water is allowed to drop from the tap-funnel on to the carbide in the flask at the rate of 6 to 7 drops a minute (the tap-funnel being filled up from time to time), and all the carbide will thus be decomposed in 3 to 4 hours. The flask is then filled to the neck with water, and disconnected from the absorption apparatus, through which a little air is then drawn. The absorbing liquid is then poured, and washed out, into a beaker; hydrochloric acid is added to it, and it is boiled in order to expel the liberated chlorine. It is then usual to precipitate the sulphuric acid by adding solution of barium chloride to the boiling liquid, allowing it to cool and settle, and then filtering. The weight of barium sulphate obtained by ignition of the filter and its contents, multiplied by 0.137, gives the amount of sulphur present in the acetylene in the form of sulphuretted hydrogen. The filtrate and washings from this precipitate are rendered slightly ammoniacal, and a small excess of "magnesia mixture" is added; the whole is stirred, left to stand for 12 hours, filtered, the precipitate washed with water rendered slightly ammoniacal, dried, ignited, and weighed. The weight so found multiplied by 0.278 gives the weight of phosphorus in the form of phosphine in the volume of gas passed through the absorbent liquid.

Objection may rightly be raised to the Lunge and Cedercreutz method of estimating the phosphine in crude acetylene on the ground that explosions are apt to occur when the gas is being passed into the hypochlorite solution. Also it must be borne in mind that it aims at estimating only the phosphorus which is contained in the gas in the form of phosphine, and that there may also be present in the gas organic compounds of phosphorus which are not decomposed by the hypochlorite. But when the acetylene is evolved from the carbide in proper conditions for the avoidance of appreciable heating it appears fairly well established that phosphorus compounds other than phosphine exist in the gas only in practically negligible amount, unless the carbide decomposed is of an abnormal character. Various methods of burning the acetylene and estimating the phosphorus in the products of combustion have, however been proposed for the purpose of determining the total amount of phosphorus in acetylene. Some of them are applicable to the simultaneous determination of the total sulphur in the acetylene, and in this respect become akin to the Gas Referees' method for the determination of the sulphur compounds in coal-gas.

Eitner and Keppeler have proposed to burn the acetylene on which the estimation is to be made in a current of neat oxygen. But this procedure is rather inconvenient, and by no means essential. Lidholm liberated acetylene slowly from 10 grammes of carbide by immersing the carbide in absolute alcohol and gradually adding water, while the gas mixed with a stream of hydrogen leading to a burner within a flask. The flow of hydrogen was reduced or cut off entirely while the acetylene was coming off freely, but hydrogen was kept burning for ten minutes after the flame had ceased to be luminous in order to ensure the burning of the last traces of acetylene. The products of combustion were aspirated through a condenser and a washing bottle, which at the close were rinsed out with warm solution of ammonia. The whole of the liquid so obtained was concentrated by evaporation, filtered in order to remove particles of soot or other extraneous matter, and acidified with nitric acid. The phosphoric acid was then precipitated by addition of ammonium molybdate.

J. W. Gatehouse burns the acetylene in an ordinary acetylene burner of from 10 to 30 litres per hour capacity, and passes the products of combustion through a spiral condensing tube through which water is dropped at the rate of about 75 c.c. per hour, and collected in a beaker. The burner is placed in a glass bell-shaped combustion chamber connected at the top through a right-angled tube with the condenser, and closed below by a metal base through which the burner is passed. The amount of gas burnt for one determination is from 50 to 100 litres. When the gas is extinguished, the volume consumed is noted, and after cooling, the combustion chamber and condenser are washed out with the liquid collected in the beaker and finally with distilled water, and the whole, amounting to about 400 c.c., is neutralised with solution of caustic alkali (if decinormal alkali is used, the total acidity of the liquid thus ascertained may be taken as a convenient expression of the aggregate amount of the sulphuric, phosphoric and silicic acids resulting from the combustion of the total corresponding impurities in the gas), acidified with hydrochloric acid, and evaporated to dryness with the addition towards the end of a few drops of nitric acid. The residue is taken up in dilute hydrochloric acid; and silica filtered off and estimated if desired. To the filtrate, ammonia and magnesia mixture are added, and the magnesium pyrophosphate separated and weighed with the usual precautions. Sulphuric acid may, if desired, be estimated in the filtrate, but in that case care must be taken that the magnesia mixture used was free from it.

Mauricheau-Beaupré has elaborated a volumetric method for the estimation of the phosphine in crude acetylene depending on its decomposition by a known volume of excess of centinormal solution of iodine, addition of excess of standard solution of sodium thiosulphate, and titrating back with decinormal solution of iodine with a few drops of starch solution as an indicator. One c.c. of centinormal solution of iodine is equivalent to 0.0035 c.c. of phosphine. This method of estimation is quickly carried out and is sufficiently accurate for most technical purposes.

In carrying out these analytical operations many precautions have to be taken with which the competent analyst is familiar, and they cannot be given in detail in this work, which is primarily intended for ordinary users of acetylene, and not for the guidance of analysts. It may, however, be pointed out that many useful tests in connexion with acetylene supply can be conducted by a trained analyst, which are not of a character to be serviceable to the untrained experimentalist. Among such may be named the detection of traces of phosphine in acetylene which has passed through a purifier with a view to ascertaining if the purifying material is exhausted, and the estimation of the amount of air or other diluents in stored acetylene or acetylene generated in a particular manner. Advice on these points should be sought from competent analysts, who will already have the requisite information for the carrying out of any such tests, or know where it is to be found. The analyses in question are not such as can be undertaken by untrained persons. The text-book on "Gas Manufacture" by one of the authors gives much information on the operations of gas analysis, and may be consulted, along with Hempel's "Gas Analysis" and Winkler and Lunge's "Technical Gas Analysis."