D. CHEMISTRY AND METALLURGY. 67 



ABSORPTION OF GAS BY CHARCOAL UNDER INCREASED 



PRESSURE. 



Mr. Hunter, of London, has lately shown that the quantity 

 of gas absorbed by charcoal increases with the amount of 

 pressure to which it is exposed, and that equal variation in 

 pressure produces nearly equal variation in the quantity of 

 the absorbed gas. 16 C',1871, 118. 



ABSORBENT POWERS OF CHARCOAL. 



Dr. Herman nVohl, of Cologne, has lately published an elab- 

 orate paper in the Archiv der JPharmacie upon the absorbent 

 power of charcoal and its application for disinfectant and de- 

 odorizing purposes, replete with suggestions of great impor- 

 tance. 



Among other deductions from his experiments, he states 

 that the carbonic acid gas obtained by heating charcoal is 

 not derived from the coal itself, but has been absorbed from 

 the atmosphere, and is held with such tenacity that it can 

 not be driven out by boiling in water, but that a temperature 

 much below that of ignition is sufficient to expel it. This 

 conclusion is the same as that which had been reached by an- 

 other experimenter, to which we have previously made refer- 

 ence. Among other facts proving this statement, Dr. Vohl 

 remarks that when charcoal has been once freed from its car- 

 bonic acid and saturated with pure oxygen, no trace of car- 

 bonic acid is appreciable, even when heated to a temperature 

 of 680 Fahrenheit. 2 C.June 8,177. 



ALKALINITY OF CARBONATE OF LIME. 



According to Mr. Skey, of the Geological Survey of New 

 Zealand, carbonate of lime is alkaline rather than neutral, as 

 shown by the fact that when prepared by igniting pure oxa- 

 late of lime in a close crucible, at a dull red heat, it gives an 

 intense alkaline reaction with reddened litmus paper, after 

 moistening with water, or after reignition with pure carbon- 

 ate of ammonia ; carbonate of lime, prepared directly from 

 chloride of calcium and bicarbonate of soda, giving the same 

 reaction with test-paper. Other experiments are specified, 

 all tending to substantiate the same general proposition. 

 5 A.October, 1870, 423. 



