I S D V S T R I A L A S D E S G T S E E R I S G CHEMISTRY
Julv 15, 1930
339
Construction and Use of Raschig's Laboratory Fractionating Column' H. M. Evans, R. E. Cornish, S. Lepkovsky, R. C. Archibald, and G. Feskov k i A T O M l C . 4 L LABORATORY, U h I V E R S I T Y OF C A L I F O R X I A , BERKELEY,
CALIF.
Fittings for t h e Raschig laboratory fractionating Dewar (4) states that silverEVERAL devices facilicolumn are described, which simplify t h e construction ing reduces the rate of boiling tate t h e u s e of the and operation of a small intermittent laboratory of liquid air to one-sixth the Raschig (17') fractionatfractionating still. I t is shown t h a t t h e natural rerate with the u n s i l v e r e d ing column-i. e., a column placement, during t h e course of the distillation, of one vacuum jacket. From Marks filled v-ith hollow cylinders liquid in t h e column by another, supplies t h e equiva(11) the radiating power of open a t their ends-on a labolent of considerable reflux heat a t cutting points, this glass (at 70" F.) is about 95 ratory scale, to deliver from heat being t h e heat of vaporization of the replaced per cent that of a "black 5 to 50 cc. of finished disliquid. The heat capacity of the column, packing, body." Taking the radiatillate per m i n u t e . T h e and jacket also contributes considerable reflux heat tion for a silvered vacuuni complete still is simple to a t t h e cutting point, b u t this heat, unlike t h e other, is jacket as 16 per cent of construct a n d operate, so proportional to t h e difference between the boiling points Uarks' black-body value, n.e that one may often allow it of t h e two successive fractions. calculate Table I. to run for hours without atA laboratory vacuum fractionating still is described, Thick insulation should be tention, although i n such as well as a simple still which recovers waste alcohol used. The relative advancases heating by steam is prefas 95 per cent by volume, t h e latter with practically no tage of commercial covrririg erable because of fire hazard. attention by the operator. I t is shown t h a t for columns over the vacuum is decreased In adopting R a s c h i g ' s operating above 100" C. t h e silvered vacuum jacket is, with smaller size pipe and column for its efficiency, as in insulating power, inferior to ordinary high-grade increased w i t h t h e larger well as simplicity, the writers commercial steam-pipe covering, assuming t h e column sizes, assuming the thickness are supported by Hill and diameter to be 2 inches (50 m m . ) or more. Results of the commercial covering Ferris (e), who found colare given of actual distillations, including attempted to be a t least as great a> the umns c o n t a i n i n g I/d-inch separation of isotopes, and t h e mixture carbon tetrapipe diameter. (6.4-mm.) Raschig rings to chloride-benzene is suggested as a standard for testing I n a t e s t (condensation be but slightly inferior to the fractionating apparatus. method, 212" F. or 100" e.) best elaborate laboratory cola 2-foot (61-em.) standard umns of similar height, arid all are inferior to TT ha
