AIDS FOR THE ANALYST Prevention of Frothing in Fischer Assay Analysis. It. P. Hensel, Research and Development Division, Pittsburgh Consolidation Coal Co., Library, Pa. assay a standard met,hod widely used to measure TyieldsFischer of coke, tar, light oil, and gas resulting from the lowHE
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temperature carbonization of coal. The method involves heating a t the standard prescribed rate a 50-gram sample contained in an aluminum retort, to which a suitable collection sj-stem for the distillation products i3 attached. The apparat,us arid procedure are fully described by Fischer and Schrader [Aiagew. Chem., 33, 172 (1920)l. Serious difficulty is encountered n - h e n assays are attemptrd on highly swelling coal>. The rapid e v o l u t i o n of gas caombined with the extreme fluidity of t h e molten bed leads to excessive frothing, u s u a l l y resulting in an overflow of the charge into the delivery orifice and thence Figure 1 to the tar trap. Selvig and Ode !IsD. EXG.CHEY., -1s.i~. bh.,7, 88 (1933)l reeomniend reducing the m i g h t of the sample to 30 grams; however, experience s h o w that certain coals perform unsatisfactorily with as little as 20 grams of sample, and reduction of sample size materially increases the significance of subsequent errdrs in handling and weighing. Glass wool acts as an extremely effective froth breaker. A weighed loose-fitting plug of Pyrex brand S o . 7220 glass ~ o o l (circa 8 grams) inserted into the retort and extending approximately 12 mm. belon- the delivery orifice (Figure 1) permits successful assays on a full charge of even the highest swelling materials. The normal procedure of weighing the coke residue directly is impractical, as some penetration of the bed into the glass wool occurs i n the course of the run. Separation of this mixture is difficult; consequently, the coke residue is best determined by subtracting the initial weight, of the glass wool from the combined vveight of residue and 11-ool a t the termination of the run.
A Cryostat. Ernst 1'. Hall and William L. h-elson, Mellon Institute uf Industrial Research, Pittsburgh 13, Pa.
Conductivity grade water used i n the cryostat was prepared by demineralizing distilled water to less than 0.1 p.p.m. impurities (as sodium chloride). The cryostat can be prepared for use in about 1.5 hours using a modification of Swietoslamki's freezJ . Phys. Chem., 47, 590-6: ing technique [Swieton-slawski, K., (1943)). [The bulb is partially immersed with occasional shaking, in an air-agitated salt-ice bath until slushy ice crystals have just formed. The bulb is removed and all but about 5 cc. of these crystals are melted by warming in the hand. The bulb is again immersed in the freozing hath (the side arm being kept just out of the bath so that it doc's not brcome rlosed) and a solid ice cake of the desired thickness is frozen. After freezing, the bulb is again momentarily warmid in thtx hand, so that a very thin \rater film is formed hetween the, i w cake and bulb wall. Placed in the glass jacket arid paccd with i c t ~ ,the cryostat is now read!, for use.] Maintenance (draining water and refilling the flask Trith ice twice daily) requires little more time than does an ordinary ice bath, the inadequacy of n-hich as :I roriptant rcf(~rcncc~ point is u.ell knoa-n.
Insulation arid maintenance as stated greatly prolong the life of the ice-water cell. The authors have repeatedly obtainecl 20 days of service, Over a period of several days in hot weather, the heat flow to the cell (as indicated by the change in the water level i n the tulle) was less than 69.1 cal. per day. This rate of heat influx is so low that equilihrium conditions can be maintained for many days. C O S T R I B ~ from I I Othe S Coal Waste Fellowship sponsored
cryostat depicted has been found invaluable for the mainT t e n a' nce of a thermocouple reference junction at 0" C. over a n extended time. The cryostat was developed by J. R. Andrrson, Physical Processes Department, Carbide and Carbon Chemicals Division, South Charleston, \V.Va., from a design suggested by Wojciech Swietosla\rski. HE
The cryostat, consists of a glass bulb (the ice-water containcr) with t x o at,tached tubes, one for filling with water and indicating by the water level the condition of the annular ice-water cell and the other for the entry of thermocouples. The ice-water cell in the bulb provides a thin layer of lrater between the ice cake and the tlicvmocouple n.cll. The lower part of the crvostat (in a yide, stoppered tube) is placed within a Dewar flask,packed with and wrapped viith towels to extend the life of the cell.
b? t h e L\-rati,rn
Pennhi.l\-ania Coal Operators Association.
Simple Refractometer Cell. Killiam G. Young and Joseph 11. Rule', Department of Chemistry, University of California, Los Angeles, Calif. the refractive index of many allylic halides Iivand other corrosive liquids, it is advisable t o protect the reDETERMINING
fractometer from the liquid, as the optical surface may be slowly 58, damaged [Winstein, S., and Young, W. G., J . Am. Chent. SOC., 2 Present address, Grasselli Chemicals Department, E. I. d u P o n t de Nemours 6 Co., Inc., Wilmington, Del.
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