October, 1923
I X D C ' S T R I A L AND ENGINEERING C H E M I S T R Y
extraction to a series of broken points which, without magnification, still showed the original outline. These changes again point to the fact that free sulfur is necessary for the successful extraction of selenium. Microscopic examination was made of sections of sulfurselenium stocks which were cured to the point where practically no free sulfur remained. The amount of selenium present was estimated by counting and measuring the particles, and, within the limits of accuracy of this method, all the selenium could be accounted for. This showed that the amount of combined selenium must be small and is not to be compared in magnitude with the amount of combined sulfur. S o further efforts were made to determine combined selenium.
*
O
' 9
1021
240 minutes' cure. This is slightly more than the normal resin content of the rubber. I n all the selenium stocks a minimum extract of only slightly more than 1.5 per cent is found. This is approximately 1.1 per cent below the original resin content of the rubber. Although selenium alone or with an accelerator is somewhat effective as a vulcanizing agent, it is apparent that it functions chiefly as an accelerator when used with sulfur. All accelerators in common use, whether organic or inorganic, are chemical compounds, but here is a case of the increased action being brought about by an element. Complications arising in the study of the accelerators of vulcanization can be greatly reduced by the elimination of many uncertain decomposition products, if selenium is used as the accelerator. The action between accelerator and sulfur is also reduced to a more simple state. It is possible that a study of the action of selenium in rubber will throw more light on the nature of acceleration.
A Ball-Mill Electrolytic Cell' By Alexander Lowy and Alfred R. Ebberts UNIVERSITY OF PITTSBURGH, P I T T S B U R GPA. H,
Mixtures of sulfuric and selenic acid may be separated in acid solution by the addition of potassium iodide. The iodine may then be titrated with standard arsenite and the selenium determined, after which the sulfate may be precipitated. This method cannot be used if a nitrate fusion has been used in the oxidation of the sulfur and selenium, unless the nitrate and nitrites are first removed. If the selenium is not t o be determined it may be reduced in the presence of a nitrate, but the presence of nitrites, which are always produced during the fusion! prevents the precipitation of selenium. This precipitation is, however, easily accomplished in acid solution by either sulfites or stannous chloride. Combined sulfur was finally determined after removal of selenium by the addition of the calculated amount of stannous chloride. The following check determinations were made by this method on a stock of known sulfur and selenium content: Sulfur Present
G.
0.0163 0.0163 0.0163 0.0163
Selenium Present G. 0.0103 0.0103 0,0103 0.0103
Sulfur Found G. 0.0162 0.0159 0.0167 0.0169
URIh'G the course of an investigation in this laboratory of the electrolytic oxidation of anthracene, a novel type of cell was designed and constructed. Certain solids in suspension have a tendency to aggregate under the action of the current. Also, when the superficial layer of any particle has entered into reaction, it prevents or slows up the action on the central portion of the particle. To prevent both of these undesirable effects this cell was designed. The stirrer was equipped with paddles to produce a swirling motion in the electrolyte, and glass balls were introduced, which were carried rapidly round and round by the swirling liquid. The thermometer and one electrode were raised enough to allow the balls to pass under them. The other electrode was on the bottom of the beaker and a connection for it was sealed in the glass. For large balls several glass marbles, such as children play with, were used, and for small ones the solid beads furnished for Hempel fractionating columns. The size of ball must be determined by conditions. Mercury as electrode has the advantage of not requiring sealing into the cell, and also that no trouble due to solids adhering to the electrode surface is experienced. The solid anodes used by the authors were sealed \ in place with Redmanol cement, which was found to be very satisfactory. Heat should be supplied by bath only. Direct heating causes the dissolution of the cell due to the different coefficients of expansion of the materials used and the excessive local heating. yE;;y:E
PIEICU'7Y
In Fig. 3 are shown the values for combined sulfur and for extraction loss of Stocks 47, 48, and 49. In all stocks containing selenium, the same stiffness is reached with lower combined sulfur. This resembles the action of stocks containing an organic accelerator. The extraction loss of the rubber-sulfur mixture reaches a minimum of 3.3 per cent a t
1
Received September 13, 1023.
ZTC
