theoretical; the chromate had 99.8 per cent of the theoretical oxidizing power, which was determined iodimetrically by the method of Bray and Rliller (1). Rubidium chromate was prepared from the hydroside and chromic oside with an over-all yield of 81 per cent,. srlIJl.\ ItT
To facilitate the preparation of cesium and rubidiuin salts from their chlorides, a laboratory-scale oscillating mercury cell has been constructed and operated to make available the pure hydroxides for these preparations. Operating instructions and data are given. Two electrolyses proved necessary to produce a hydroxide virtually free of chloride, other impurities also being removed to a considerable degree, Toward the end of an electrolysis, the cell requires dose attention if efficient operation is desired. Care is necessary throughout in order to minimize losses whenever expensive materials are being processed. The chief drawback encountered was a contamination-not serious in the present case-of the hydroxide by sodium ion derived from glass. This contamination could be prevented by building cell and containers of more alkaliresistant materials. In this work the hydroxides, carbonates, and chromates of cesium and rubidium were prepared, as mere also cesium azide and dichromate. REFERENCES (1) BRAYAND MILLER: J. Am. Chern. SOC. 46, 2204 (1924). (2) FETZER: J. Phys. Chern. 82, 1787 (1928).
HEAT GUARL) FOR THE McBAIS-BAKR SORPTION BALANCE R E N E D . ZENTNERI- 3 Department of Chemistry, Stanford University, California Received March 11, 1947
Of the numerous techniques presently utilized in the measurement of the weight changes of various materials during sorption, probably the simplest, most reliable, and most accessible is that known as the McBain-Bakr sorption balance (2). By the proper manipulation of this method, isobars, isotherms, and isosteres of various two-component systems may be conveniently, accurately, and reproducibly studied. In general the sorption characteristics of such relatively stable materials as soap (3), textiles, and inorganic materials (1 ) have been investigated, with respect to both water and liquid hydrocarbons. Lever Bros. Company Research Assistant to Professor J. W. McBain. Present address: Patent Division, Plastics Department, E. I. du Pont de Nemours and Company, Arlington, New Jersey. 1 2
H E A T GUARD FOR THL, IIcBAIA-I{ %hR SORY’I 101. RALA4CI’
973
The erratic and irreproducible results obtained from studies of dehydrated milk-water and aluminum soap-water systems prompted Dr. Karol J. Mysels of Stanford University to suggest that some factor in the construction of the balance itself was introducing error. It was found that during the sealing and glassblowing of the balance unit, enough heat was trannsniitted to affect unstable samples significantly. I t was necessary to devise a suitable shield that would guard unstable samples from radiant heat nithout interfering with the function of the balance itself. As is known in the literature, the RlcBain-Rakr sorption balance is customarily employed for investigations and determinations of sorption isotherms for solid-liqiiid systems. The balance itself ConsiSts of five major components: II
COPPER
FOll
FIG.1. Hest guard for the McBain-Bakr sorption balance
Pyrex-glass tube (A) sealed a t both ends, containing a platinum bucket (Bi which contains several milligrams of the sample (D) and is suspended by a helical spring (C) over a reservoir of liquid (E). The entire assembly, evacuated and hermetically sealed, is generally maintained in a two-zone oven (4) provided with suitable windows of such nature that the extension of the spring may be measured a t various humidities and temperatures with the aid of a cathetometer sorbed liquid) weight required to produce such extension and the (sample calculated from Hooke’s 1aTY. The last operation in the construction of the balance is that of sealing the top of the balance during evacuation; the neck-down, seal-off, and anneal steps are customarily conducted with an oxghydroge: torch and a t several points the Pyrex glass is worked a t white heat. It was discovered that heat radiation
+
from the heated glass produced changes not only in the weight but also in the appearance of various relatively unstable samples. The above factors make necessary the use of B protective device that will completely block do\m\vard radiation and will lie inert, containing no reacting or interfering components. Copper discs sealed within a glass capsule form a satisfactory type of guaid. Gin. Pyres test tube lvhose outside diameter is of such calibre aH t,o fit smoot,hly inside the 22-mm. Pyres tube (A) is cleaned and filled t,o about 5 half inch in depth with copper discs (cut from copper foil with :in old cork-borer). The test tube is “necked down,” evacuated to the limits of a IIyvac pump’s capacity, and the neck sealed off to yield such a capsulr as illustrated. small glaes hook was added to the top of the capsule t,o facilitate its insertion and removal from the balance. The capsule is then inserted within the unsealed balance unit to rest, on the nirhrome wire spring-loop (F);t.he loop is made with protruding ends to insure its stability wit,hin the tube (A) REFERENCES (1) HIYTLER, S. S., FISCHER, E. A,, AND FREEMAX, I. R . : J. Am. Chem. Soc. 66.1009 (1943). (2) MCBAIX,J. W . , AND BAKR,A. M.: J. Am. Chem. SOC.48,690 (1926). ( 2 ) MCBAIN,J. W., AND LEE, W. W.: Oil & Soap 20, 17 (1943); Ind. Eng. Chem. 36, 784
(1943). (4) SHREVE, G.
W . : Ph.D. thesis, Stanford University, 1946.
ALUMINUM DILAURATE AS ASSOCIATION COLLOID I K BEXZENE’ JAMES W . McBAIS
AND
EARL B. WORKING
Ijeparlmenl of Chemistry, Stanford University, California Receiced March IS, 1947
Ordinary soaps in \vat,er are the best known esamples of association colloids. Jn them ions and molecules spontaneously associate to form colloidal particles or micelles, and these micelles are in true reversible equilibrium with the ions and molecules from which they form. It is characteristic of such colloids that the particle weight or apparent molecular weight is a function of concentration and temperature. The present investigation brings evidence for the existence of an associatioil colloid in a non-aqueous solvent, (1) : namely, aluminum dilaurate, ill(OH)L?,in benzene. This is sho\vn by the change in osmotic pressure with concentration, which contrasts strongly with the behavior of a polymeric colloid, and is confirmed by viscosity measurements. 1 Study conducted under Contract OEMsr-1057 between Stanford University and the Office of Emergency Management. recommended by Division 11.3 of the National Defense Research Committee and supervised by Professor J. W. McBain.
