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CURRENT TOPICS.
[J. F. I.
A g r i c u l t u r a l L i m e . - - R . C. COLLISON of the New York Agricultural Experiment Station at Geneva states in Bulletin 478 of that station that at least 5° to 75 per cent. of the soils of t h a t state would be distinctly benefited by the addition of suitable basic material. T h e following s u b s t a n c e s are used for this p u r p o s e : B u r n e d lime, h y d r a t e d lime, g r o u n d limestone, and lime byp r o d u c t s ; usually the m o s t economical is a good g r a d e of g r o u n d limestone with a calcium c a r b o n a t e equivalent of over 9 ° per cent. If g r o u n d limestone be applied at the rate of 50o to IOOO pounds per acre, it should all pass a 4o-mesh screen ; if applied at the rate of 2 or more tons per acre, it need only pass a Io-mesh screen. T h e smaller a m o u n t should be applied yearly, while the heavier t r e a t m e n t is required but once e v e r y three to five years. M a g n e s i u m limestone m a y be used for agricultural purposes. L i m e stone screenings and crusher dust (a by-product in the manufacture of crushed stone) frequently are a fair grade, cheap material suitable for use in liming soils. J. S. H. Alcohol as a M o t o r F u e l . m P r e l i m i n a r y researches by H. B. D i x o n on the use o f alcohol as a motor fuel are described in Jour. Soe. Chem. Ind., 192o , xxxix, Review, 355. Alcohol was found to possess m o s t of the p r o p e r t i e s which are characteristics of a good m o t o r fuel. I t s caloric value is l o w e r than t h a t of petrol, but it m a y be used under higher p r e s s u r e s t h a n the latter. T h i s p r o p e r t y of high ignition t e m p e r a t u r e under c o m p r e s s i o n is changed b u t little b y a d m i x t u r e of 2o per cent. of benzene or of petrol. Such a m i x t u r e starts readily in the cold, and runs v e r y s m o o t h l y in an engine.
j. s . H . C o l l o i d s . w F r o m a critical s t u d y of colloids, H. D. MURRAY
(Science Progress, I92O, xv, 234-242 ) concludes t h a t the deepest insight into dispersoid s y s t e m s has been given by the phen o m e n a of coagulation, and t h a t future k n o w l e d g e of colloids will p r o b a b l y come f r o m that direction. J. s. H. N a t u r a l D e p o s i t s of P o t a s h . - - H . D. RUHZ~I u r g e s that search for natural deposits of soluble p o t a s h salts be m a d e in the salt fields of N e w York, Ohio, and Michigan b y m e a n s of core drilling. D e p o s i t s of p o t a s h salts, similar to those of Stassfurt, are likely to exist in a n y salt beds of considerable thickness. I n a search of this nature, a s a t u r a t e d brine m u s t be used for the liquid in the core drills. (.four. Ind. and Eng. Chemistry, I92O, xii, 837-84o.)
j. s. H.