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T H E J O V R A - A L OF I S D U S T R I A L .45D E.\‘GISEERI&YG
THE DETERMINATION OF PHOSPHORUS IN COMMERCIAL ACETYLENE. B y L.M. DENNISASD W. J. O’BRIEN. Received May 28, 1912.
Acetylene that is prepared by the action of water upon calcium carbide almost always contains gaseous compounds of phosphorus that arise from the calcium phosphide in the carbide. If the acetylene is generated by dropping water upon the carbide, the high temperature resulting from the localized action of the two substances may give rise to a considerable amount of organic phosphorus compounds. On the other hand, if appreciable rise of temperature during the generation of the gas is avoided, practically all of the phosphorus in the acetylene is in the form of phosphine. The amount of phosphine in crude acetylene is quite variable, but i t usually lies between 0.03 per cent. and 1.8 per cent.’ Of the methods that have been proposed for the determination of the gaseous compounds of phosphorus in acetylene, the combustion method developed by Eitner,a Keppeler,a and Fraenkel,4 and the sodium hypochlorite absorption method of Lunge and Cedercreutzj are in most general use. The first of these methods, in which the phosphorus in crude acetylene is determined by burning the gas and ascertaining the phosphoric acid in the products of combustion, gives the total amount of phosphorus, whether i t is present in the gas as phosphine or as organic phosphorus compounds. The acetylene is burned in an acetylene Bunsen burner under a cyfindrical glass hood, and the products of combustion are drawn through an oxidizing solution, such as sodium hypochlorite or hypobromite. The resulting phosphoric acid is then determined by precipitation with “magnesia mixture.” On account of the difficulty in regulating the pressure of the gas as it comes from the evolution apparatus, Fraenkel recommends that the acetylene from about 50 grams of calcium carbide be collected over a salt solution in a large tubulated bottle, and that the gas be then driven from this bottle through the burner. This necessitates the use of glass bottles of about 2 0 liters capacity, and if the acetylene is t o be mixed with an equal volume of hydrogen before combustion, as Fraenkel recommends, the containers must be so large as t o render them very unwieldy and quite expensive. Moreover, the accuracy of the determination of phosphorus in the gas will undoubtedly be affected by the reaction between the compounds of phosphorus and the confining liquid. For these reasons the method of Lunge and Cedercreutz in which the crude acetylene is passed directly from the generating apparatus through a solution of sodium hypochlorite is to be preferred to the combustion method if it will yield accurate results Objection has been raised to this absorption method because the acetylene is generated by dropping water 1 Vogel, Handbuch f u r Acetylea, page 234. The analyses given by Fraenkel, J. Gasbel., 61, 431 (1908), show from 0.024 t o 0.057 per cent. by volume of phosphine in crude acetylene. 2 J . Gasbel., 44, 548 (1901); 3 Ibid., 46, 802 (1902). 4 Ibid.. 61, 431 (1908). 6 Z . angew. Chem., 651, 1897.
CHEMISTRY.
Nov., 1912
on the calcium carbide, which gives rise to organic phosphorus compounds that escape complete oxidation. In seeking to improve this absorption method, the two points that present themselves are therefore : ( I ) A method of generating acetylene that will avoid appreciable rise of temperature when the calcium carbide is decomposed, and ( 2 ) An absorption apparatus that is more efficient than the ten-bulb tube used by Lunge and Cedercreutz. The evolution of acetylene without marked rise of temperature was accomplished easily by the employment of a small Kipp apparatus about 40 cm. high, and with bulbs about I O cm. in diameter. The annular space around the stem between the middle and bottom bulbs is covered with a perforated rubber disk, D (Fig. I ) . A solution of sodium chloride, saturated a t room temperature, is poured into the top bulb
until the end of the stem in the bottom bulb is covered with the liquid. A perforated stopper carrying a short glass tube is inserted in the neck of the top bulb, the stopper with exit tube and glass stopcock is inserted in the tubulus of the bulb B , and the further end of the outlet tube is connected with the absorption apparatus that contains the solution of sodium hypochlorite. Hydrogen gas is now passed into the upper bulb of the Kipp generator, and through the absorption apparatus t o displace the air. About 50 grams of the calcium carbide under examination, broken into pieces about the size of a pea and sifted to remove the dust, is placed in a dry weighing tube which is a t once tightly stoppered and weighed. When practically all of the air has been displaced from the Kipp apparatus by hydrogen, the stopper in the tubulus of the bulb B is removed, the contents of the sample tube is poured into the bulb and the stopper is a t once reinserted. The current of hydrogen through the apparatus is continued for about five minutes, the stopcock then closed, and the stopper and tube are removed from the upper bulb of the Kipp generator. An additional amount of salt solution sufficient to cause the apparatus t o function as a gas generator is then introduced into the upper bulb. The stopcock is now opened to such a n extent that the evolved gases pass through the apparatus a t a rate slightly faster than will permit of the bubbles being counted. Under these conditions the decomposition of a sample of 50 grams will be
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Nov., 1912
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G CHEi'MISTRY.
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effected in about two hours. The reaction between and after the reaction, and the loss in weight equals the the salt solution and the calcium carbide proceeds a t weight of the evolvedgases, which are here assumed t o a uniform rate, and with no appreciable rise of tem- consist entirely of acetylene. The total weight of the perature. Bamberger apparatus before the decomposition of The absorption apparatus employed is a Friedrichs the carbide amounts to from j5o to 800 grams. This gas washing bottle modified so that the apparatus can weight may be materially reduced by employing, in easily be rinsed out with water at the close of the run. place of the Wolff bottle, a n Erlenmeyer flask of about The absorbing solution is introduced into the outer 2 5 0 cc. capacity. This is fitted with a two-hole rubber cylinder to such height t h a t it will stand a t the top of stopper into one opening of which is inserted the stem the widened foot of the cylinder, and the spiral with of a small separatory funnel of 1 2 5 cc. capacity; the the ground glass shoulder is then inserted. When a other opening of the stopper carries a U-tube filled gas is passed into the bottle through the central tube, with calcium chloride. A sample of the calcium cari t follows the grooves of the spiral when it rises and bide amounting to about 50 grams is accurately pushes some of the solution ahead of it. These gas weighed in a weighing bottle, and is then introduced washing bottles are much more compact than the ten- into the flask. The stopper carrying the separatory bulb tube used by Lunge and Cedercreutz, and experi- funnel and the U-tube is then inserted, and the funnel ment has shown t h a t the absorption attained by their is filled with a 2 0 per cent. solution of sodium chloride. use is surprisingly rapid and complete. The solution The whole apparatus is then weighed on a balance of sodium hypochlorite with which the absorption accurate to 0.01 gram. The total weight of this apparatus is charged is prepared by dissolving 1 5 modified form of the Bamberger device is approxigrams of sodium hydroxide in I O O cc. of water, satu- mately 300 grams. The salt solution is now allowed rating the solution with chlorine, driving out the to drop slowly upon the calcium carbide, and, after excess of chlorine with a current of air, and then de- decomposition is complete, dry air is passed through termining the amount of sodium hypochlorite in the the apparatus to expel all of the acetylene. The apsolution by treatment with hydrogen dioxide in a paratus is then again weighed, the difference between Lunge nitrometer. The solution is then diluted to the two weighings giving the weight of the acetylene three per cent. NaC10, and about j j cc. of this solution evolved. One kg. of chemically pure calcium carbide yields 405.93 grams of acetylene, equivalent t o 348.4 is placed in each bottle. After the decomposition of the calcium carbide is liters of acetylene under standard conditions. Ascomplete, the acetylene that remains in the generator suming that the loss of weight in the apparatus equals is driven over into the absorption bottles b y again the weight of the acetylene evolved, the volume of passing hydrogen through the apparatus in the manner the liberated gas may be calculated as follows: Weight of Sample : Weight C2Hz = 100 : x above described. The contents of the gas washing x = the weight of evolved acetylene expressed in bottles are then transferred to a beaker, the bottles and inner tubes being thoroughly rinsed with distilled per cent. of weight of the calcium carbide. Since pzire calcium carbide will yield acetylene water: I O cc. of concentrated hydrochloric acid is added t o the liquid, which is then boiled until the amounting to 40.593 per cent. of the weight of the calodor of chlorine is no longer noticeable. Ammonium cium carbide, 40.593 : per cent. CzH. by weight = 348.4 : x hydroxide is added t o alkaline reaction and the phosx = the number of liters of acktylene evolved from phoric acid present is determined by precipitation with magnesia mixture, weighing as magnesium pyro- one kilogram of the calcium carbide under examination, or the number of cubic centimeters evolved from one phosphate. The volume of phosphine, t o which the weight of gram of the carbide. From the above data the per cent. by volume of the magnesium pyrophosphate is equivalent may be calphosphine in the acetylene may now be calculated. culated as follows: An example of such a calculation follows: %,Pz07 : 2 PH3 = 222.i2 : 68.13, or weight MgzP20r X 0.3059 = weight phosphine. Since one gram of phosphine occupies a volume of 657.9 cc. a t ' 0 C. and 760 mm. pressure, volume of PH3 in cc. = weight in grams MBZPZOI X 0.3059 X 657.9 or, volume of PH3 in cc. = weight in grams MgzPpO7 X 201.25.
It is customary t o report the results as the per cent. by volume of phosphine in the evolved acetylene. This necessitates the determination of the volume of gas that is liberated by the calcium carbide under examination. The most convenient method for making this determination is t h a t proposed by Bamberger' who places a definite amount of the carbide in a weighed twoneck Wolff bottle of about 400 cc. capacity, and runs in upon the carbide a n amount of a saturated solution of sodium chloride sufficient t o entirely decompose the substance. The whole apparatus is weighed before Z. Calc. A d . , 1, 210 (1898).
A. DETERMINATIOX O F PHOSPHINE. Calcium carbide taken = 50.3548 grams. = 0 0089 gram. Weight of MgZPZO7 0.0089 X 201.25 50,3548 = 0.035 cc. cc. PHa from 1 gram CaCz =
B. DETERMINATION O F Y I E L D OF ACETYLENE. Calcium carbide taken
-
41.071 grams. 14.4885 grams. 41.071 : 14.4885 = 100 : per cent. C2Hs by wt. Per cent. G H 3 by weight 3 35.28. 40.593 : 35.28 = 348.4 : cc. ClHz from 1 gram CaCz. Volume CzH2 from 1 gram CaCz = 300 cc. cc. PH3 from 1 gram CaCz X 100 Per cent. PHQby volume = ~ ~ _ _ _ = _ 0.011770. ~ cc. CzHz from 1 gram CaCz
Loss of weight of apparatus
3
~~
To determine the accuracy of the results yielded b y this method, i t was necessary t o ascertain: ( I ) Whether the gaseous compounds of phosphorus absorbed by sodium hypochlorite would be entirely
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T H E J O U R N A L OF I N D U S T R I A L A N D EA'GINEERING C H E M I S T R Y .
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taken up by two Friedrichs gas washing bottles containing the reagent, and ( 2 ) Whether in the method here employed for the generation of the acetylene, any gaseous compounds of phosphorus are evolved that are not absorbed by sodium hypochlorite. That complete absorption of the compounds of phosphorus is obtained with only two of the gas washing bottles of the type here described, even when a sample of carbide unusually high in phosphorus is used, was demonstrated by connecting four of the absorption bottles in series, charging each with 7 5 cc. of a 3 per cent. solution of sodium hypochlorite and testing the contents of each for phosphoric acid after the run. I n no case was this acid detectable in the third or fourth bottle. The second query was answered in two ways: The gases issuing from the second absorption bottle were burned with an excess of oxygen, and the products of combustion werefoundto befreefromphosphoric acid. I n another experiment, the crude acetylene from the generator was burned directly without being passed through the solution of sodium hypochlorite, and the result was found t o agree with that obtained by the absorption method. The combustion of acetylene as i t issues from a bottle containing a liquid absorbent has heretofore presented difficulty because of the intermittent flow of the gas. It was found, however, that complete combustion is easily attained by passing the acetylene into the hydrogen inlet tube of a Linnemann oxyhydrogen lamp; admitting oxygen into the other tube of the lamp, and insuring continuous combustion by causing a small horizontal flame, about I cm. long, of illuminating gas that is free from phosphorus t o burn across the orifice of the lamp. The accuracy and uniformity of the results obtained with the method here described are shown in the following tabulation of analyses by the absorption method, and by the method of combustion.
No. 1 2 3 4 5 6
7 8 9 10 11
TABLEI . This sample CaCz yielded 300 liters CzHz per kilogram. Per cent. of phosphine in evolved acetylene Weight of Weight of sample in MgzPp07 by NaClO by combustion grams. in grams. method. method. 50.3548 0.0089 0.0117 .... 50.3572 0.0073 0.0097 .... 50.1870 0.0062 0.0083 .... 50.3027 0,0050 0.0066 .... 50.0036 0.0062 0.0083 .... 50.3047 0.0059 0.0078 .... 50.1625 0.0059 0.0078 .... 50.0000 0.0072 .... d.0096 50.0000 0.0047 .... 0.0063 50 .OOOO 0.0060 .... 0.0080 50.0612 0,0062 .... 0.0083 Average
-
-
0.0086
0.0080
The results given in Table I were obtained with a sample of commercial calcium carbide. To ascertain whether the method would give uniform results when the acetylene contained a relatively large amount of phosphine, the authors prepared a sample of calcium carbide high in phosphorus, and the analyses of this
Nov., 1912
product by the two methods are given in Table 11. TABLE11. This sample CaCz yielded 287 liters CzH2 per kilogram. Per cent. of phosphine in evolved acetylene Weight of Weight of MgzPZOi by NaClO by combustion sample in grams. in grams. method. method. 50.0651 0.0661 0.0925 .... 50.0200 0.0592 0.0829 .... 50.0432 0.0782 0.1093 .... 50.1004 0.0582 0.0814 .... 50.0600 0.0680 .... 0.0948 50.1043 0.0641 .... 0.0896 50.061 2 0.0601 .... 0.0841 50.0121 0.0642 .... 0,0899 I
SO.
1 2
3 4
5 6 7 8
-
-
Average, 0.0915
0,0896
CORNELL UNIVERSITY, ITHACA, N. 31.
THE DETERMINATION OF LEAD SULPHATE AND THE ULTIMATE ESTIBfATION OF SUBLIMED WHITE LEAD IN RUBBER. By JOHNA. SCHAEFFER. Received Aug. 9, 1912.
The extended use of sublimed white lead in the compounding of rubber and the gradual establishment of specifications regulating the content of sulphur allowable in certain grades of rubber, has brought forth the necessity of having some accurate and rapid method for the determination of lead sulphate in finished rubber. Sublimed white lead as placed on the market is a basic sulphate of lead showing the following average percentage composition: Lead sulphate.. . . . . . . . . . . . . . . . . . . . . . . Lead oxide.. . . . . . . . . . . . . . . . . . . . . . . . . . Zinc oxide. . . . . . . . . . . . . . . . . . . . . . . . . . .
Per cent. 78.5 16.0
5.5
The lead sulphate and lead oxide are chemically combined as basic sulphate of lead and the compound consists of extremely fine, amorphous particles. It is believed that the vulcanization of the rubber causes a decomposition of the sublimed white lead with the consequent formation of lead sulphide by union of sulphur with the lead oxide, which accounts in a measure for the remarkable results obtained when this compound is added to rubber. After the vulcanization the inert compounds, lead sulphate and lead sulphide, remain. It is this property of rapid reaction, due to the extreme fineness of the particles, and the resultant formation of the inert compounds, which is causing the rapid increase in the use of sublimed white lead in the compounding of rubber. Manufacturers, however, have restrained themselves from any extended use of the above compound in all gradesof rubber which is sold under specifications, owing t o the limited content of sulphur allowable, this sulphur being total sulphur regardless of whether the same is in an active or a n inactive form. I t has been known for some time that such specifications should not include sulphur which is present in an inactive form as is found in the case of the lead sulphate present through the addition of sublimed
