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 .
836
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
Nov., 1912
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 C H E M I S T R Y .
white lead to rubber, provided some mFthod for the differentiation of the active form from the inactive form be applicable. Recent agitation on the above question led to work in our laboratory with the result that the following method was found to give accurate and rapid results for the determination of lead sulphate in finished rubber. A two gram sample of the rubber under examination is placed in a hard glass tube, A , about one inch in diameter and about eight inches in length. The one end of this tube is connected to a carbon dioxide
x' generator, D , the carbon dioxide evolved passing through a bottle, E , containing water. The other end of the tube is closed with a stopper holding a small tube for the escape of the gas and decomposition products. Carbon dioxide is continuously generated by the action of hydrochloric acid on limestone. After all the air in the apparatus has been replaced by carbon dioxide, the rubber in the hard glass tube is very gently heated until all the organic matter is driven off and the rubber has become a dry mass. Under these conditions all interfering organic matter is removed without the possibility of any oxidation of sulphur or sulphide t o sulphate. After complete decomposition, the tube is allowed t o cool while carbon dioxide passes through the apparatus. The contents of the tube are then carefully and completely removed with a spatula, the hard mass being carefully ground in a small agate mortar and the finely ground residue placed in a small flask which is connected to the carbon dioxide generator in place of the hard glass tube. The powder in the flask is now treated with 2 j cc. of concentrated hydrochloric acid. The air is replaced by carbon dioxide and the contents of the flask gently boiled until all the sulphides are decomposed and any hydrogen sulphide evolved is driven off. This boiling will require from fifteen t o twenty minutes. The decomposition of the mass by concentrated hydrochloric acid in the presence of carbon dioxide mill remove any sulphides without chance of oxidation to sulphate and will dissolve practically all the lead sulphate. After the sulphides are decomposed, the acid in the flask is diluted with water, the solution is filtered, and any residue is thoroughly washed with hot water. The residue remaining is ignited in a porcelain crucible, then digested with concentrated
83 7
hydrochloric acid, the solution diluted, filtered, washed, and added to the original filtrate. I t was found that from 0 . I to 0 . 2 of one per cent. of lead sulphate remained in the residue. The greater portion of the free acid is neutralized with ammonium hydroxide and final neutralization is reached by the slow addition of sodium carbonate, after which about two grams in excess of sodium carbonate are added. The solution is boiled for fifteen minutes, filtered and thoroughly washed. By this process all the lead is removed as carbonate. The sulphate present in the filtrate is precipitated with barium chloride, the usual conditions being observed. The sulphate is weighed as barium sulphate and calculated to sulphur and lead sulphate. For the calculation of lead sulphate to sublimed white lead, the average composition of sublimed white lead is used, namely, divide the lead sulphate found by 7 8 . 5 per cent. This calculation must be made for determining the percentage of sublimed white lead present, as in no way can the original lead oxide in sublimed white lead be determined when once subjected to the process of vulcanization. However, as sublimed white lead varies but slightly in chemical composition, the result in this case will be quite accurate. By the use of this method the following results were obtained on five different samples of rubber compounded with sublimed white lead according t o various formulae : Sample No. I was compounded with Ceylon, sublimed white lead, litharge and sulphur. The percentage of sulphur added through the use of sublimed white lead was definitely known. The analysis showed the following: SAMPLE No. 1 . Percentage of sulphur added by the use of sublimed white lead = 2 . 1 4 . Percentage of sulphur found present Lead sulphate as lead sulphate. found. 2.31 2 19 2.25 2 25 2.17
21.92 20.74 21.31 21.31 20.54
Sample No. z was also compounded from Ceylon, sublimed white lead, litharge and sulphur in widely different proportions from sample KO. I . The analysis showed the following concordant results on the percentage of sulphur present as lead sulphate. SAMPLENo. 2.
Percentage of sulphur found present as lead sulphate. 3.98 4.02 3.99
Lead sulphate found. 37.70 38.09 37.87
Sample No. 3 was compounded from sublimed white lead, zinc oxide, litharge and sulphur; the variety of rubber used, was, however, not submitted. The exact percentage of sulphur added through the use of the sublimed white lead was here again known. Six determinations gave very concordant results.
T H E J O U R S A L OF ILYDCSTRIAL: A-YD E,\7GIAYEERIiZ'G C H E M I S T R Y .
838
SAMPLE No. 3. Percentage of sulphur added by the use of sublimed white lead = 1 36. Percentage of sulphur found present Lead sulphate as lead sulphate. found. 1.42 1.41 1.36 1 .46 1.46 1.41
13.45 13.40 12.89 13.83 13.86 1.3.39
Sample No. 4 was compounded with zinc oxide, sublimed white lead, litharge, and sulphur, though in different proportions from sample No. 3. The analysis showed the following: SAMPLE No. 4 . Percentage of sulphur found present as lead sulphate.
Lead sulphate found
1.33 1.34 1.32
12.65 12.72 12.59
SAMPLENo. 5 .
1 .oo 1.03 1.03 0.99
9.49 9 77 9.74 9.39
Sulphur found in
No. 5 as sulphate,
3.98 4.02 3.99
Lead sulphate found. 37.70 38.09 37:81
when mixed with freshly precipitated lead sulphide and decomposed in the usual manner. Two determinations. 4.03 4.06
Lead sulphate found. 38.19 38.43
0.145 0.148 0.171
Sample No. 7 , compounded with zinc oxide and sulphur, showed the following: SAMPLE No. 7 Sulphur present as sulphate. Per cent. 0.10 0.09
Lead sulphate found.
I n order to determine whether there was any possibility of the oxidation of the lead sulphide, usually found in rubber, to lead sulphate during the decomposition, the following experiments were carried out. Lead sulphide was freshly precipitated, filtered, thoroughly washed and dried. This was examined before using for lead sulphate. Two grams of sample No. 5 rubber were then thoroughly mixed with one gram of this lead sulphide and the decomposition was carried out in the usual way. The following results showed that no such oxidation had occurred:
Sulphur found in No. 5 as lead sulphate when decomposed in the usual manner. Three determinations
The sampFs were compounded according to different formulas, the one being made from Ceylon, litharge and sulphur, and the other from zinc oxide and sulphur, the variety of rubber used, however, not being given. A small percentage of sulphur present as sulphate was found in each case, but as the results on each sample were concordant, yet varied on the two samples, i t is obvious that the danger of oxidation of sulphide t o sulphate is slight, provided all the oxygen is removed from the apparatus by carbon dioxide before any decomposition is begun. The results showed the following sulphur values on sample No. 6 compounded with Ceylon, litharge and sulphur: SAMPLE N O . 6. Sulphur found as sulphate. Per cent.
Sample KO. 5 was a sample submitted for examination for the purpose of estimating the lead sulphate present. None of the other constituents were given. The concordance of the lead sulphate determinations was exceptionally good. Percentage of sulphur present as lead sulphate.
Nov., 1 9 1 2
.
Two samples of rubber which were compounded without the addition of sulphate in any form were then examined by this method of analysis, t o still further determine whether there was any possibility of oxidation of sulphide to sulphate during the composition.
The slightly higher values for sulphur found present as lead sulphate in the samples examined where the content of sulphur present through the addition of sublimed white lead was definitely known may be due to this exceedingly slight oxidation of sulphide to sulphate, most probably during the process of vulcanization. From the above results it will be seen that the percentage of sulphur present in rubber as lead sulphate can be accurately determined apart from the free sulphur and sulphide present in rubber. I t will be noted that the sulphur present in the inert form as lead sulphate can be readily differentiated from other forms and eliminated in such cases where specifications call for a definite percentage of sulphur, by a determination of the sulphate in the above manner, and its subtraction from the total sulphur present. I n accuracy and rapidity the method will be found to yield far better results than can be obtained by any of the other known methods for this determination. Additional experiments are a t present being begun toward the perfection of a method which will determine the percentage of lead sulphate present in rubber when compounded with sublimed white lead where other compounds such as calcium sulphate, calcium carbonate and barium sulphate are added. While this is purely a n inorganic separation, i t is hoped that a rapid method for such differentiation will be found, This paper serves as a preliminary one to a future paper in which this separation will be presented. LABORATORY O F PICHER LEADCO.. JOPLIN,Mo.
