Distillation of Rubber Cement. Jerome L. Been, Martin XI. (:rover, and Kenneth J. Ewing, Rubber R. Asbestos Corp., Bloomfield, Ti.J. HE following method has been found useful in application of r r Engler distillation ( 1 ) to rubber cement, to determine whether t n o cements have the same solvent combination or to determine the :tniount and kind of solvent present in a cement of unknown coniposit,ion. The equipment is set up as directed by the hmerican Society for Twting Materials ( I ) , and 100 grams of rubber cement are c.li:irgd into the flask. An oil bath is used to prevent local oveIIw:rting and subsequent decomposition of the cement. I t is convenient to collect the solvent on a tared balance, recording temperatures a t every 2 grams of solvent recovered. I u order to carry the distillation to completion, 0.5 gram of high-boiling silicone oil is added. Without it, the cement will foaiii and slug over and the rubber film will not break to a l l o ~ tlw solvent to escape at the required rate. The silicone oil must 1x1 sufficiently high boiling so that it will not distill over (the oil paitic.ularly recommended is KO. 9981LTSV70, made by the C;ciic~alElectric Co., Schenectady, S . Y.), Such an oil exert8 :Lnegligible effect on the vapor pressure of the solvent. It is probable that other high-boiling surface active agents may be used in place of silicone oil. The procedure is also suggmtrd f u r use with other high polymer solutions of high viscosity.
In routine polarographic analysis, most of the previous designs suffer from the disadvantage that they are of delicate construction, elaborate in design, and because of the necessity of removal to clean and recharge them, are subject to breakage. Time is alRo consumed in the removing and cleaning operation. Specifications. Outside diameter of the jacket is 80 111111. In.side diameter of the solution chamber is 55 nun. Depth of aolutiori chamber, to cone, is 38 mm. A stopcock, size 2, narrow bore is used. Tubing i8 8 mm. in outside diameter. Borasilicate glasb, 1.5 mm. thick, is used in the body of the cell. The present cell (Figure 1) was designed to provide a unit for routine use. I t is permanently mountable, by the use of :I finger-type clamp, and incorporates the following features : construction of heavy borosilicate glass; a thermal jacket, ;i, through which n-atrr from a constant-temperature bath is circulated, a combination gas and drain tube, B , to provide rapid draining and cleaiiiiig (through D )as well a6 to allow the passage of inert gas (through E ) to the solution to be analyzed, depending upon the position of the stopcock, C. The cell as normally used in this laboratory is fitted with I large (size 12) rubber stopper through which are passed a gas-exit tube built to contain a thermometer, G, a reference anode, F , and the dropping mercury electrode, H . The silver-silver chloride combination using 1 N potassium chloride as electrolyttz i i employed as the external anode. The cell is capable of analyzing a minimum of 10 and a niusimum of 50 ml. of solution. ACKNOWLEDGMENT
LITERATURE CITED I 1I
.-\tiierican Society for Testing Material.;, Philadelphia, Pa. ‘,StandardMethod of Test for Distillatioil of Gasoline, S a p h tha, Kerosene, and Siniiltn, Petroleum Products,” A.S.T.hI. 1)esignation D 50-46.
The author wishes to acknowledge the assistance of Ray I. ’ .
~)lic~:ition~. Lingane ( 3 ) designed a cell for rapid analysis, while 1,:uigt.r ( 1 ) describes a unique cell incorporuting an external reference :mode. Other general types : I W discussed in the review of polarographic instrumentation b y Lingnne (e). 1
I THOUGH
solutions of potassium hydrogen tartrate are
wii-
24’venient standards for the calibration of pII equipment, many
may not be aware that the pH may be changed in a relatively short time by molding. Hitchcock and Ta>-lor(3)stutlird R 0.03 .lf solution and noted a susceptibility to mold growth, hut did not estimate the resulting change of pH. Lingane ( 4 ) rerommended a saturated solution of potassium hydrogen tartrate \)ecause of its ease of preparation, reproducibility, and adequate huffer capacity, but made no mention of the tendency to mold. .%]though he otiserved an increase of only 0.03 pH unit after a year, Linganr suggested that the solution br freshly prepalcd :I+ needed. At the time of preparation, the pH of the 0.03 X solution w:is found t o be 3.569 a t 25’ C., as compared with 3.567 given 11)Hitchcock and Taylor ( 3 ) and 3.569 to 3.575 computed by the writer ( 1 ) from the e.m.f. of cells without liquid junction. h fluff of mold appeared in about 14 days. At 54 days the pH w w found to have risen to 3.591 and, after 93 days, to 3.609. The initial pH of three saturated solutions was found to lw 3.561 * 0.003 a t 25’. One of these solutions molded in 7 day.; and was found 18 days later to have a pH of 3.660, or 0.1 unit higher than its original value. The p H of another remained unchanged for 13 days and there was no noticeable molding. Three weeks later mold had formed and the pH had risen 0.06 unit to UPPI’S
I’rpsvnt address. 1RIon-anto Cliruiicnl Co.. St. Loi;i>, 110.
n
Frederickson Cell
813
