Dr. T. Thomson on Pyroxylic Spirit and its Compounds. 47 



oily product. Finally, it blackens slightly, and the barytes is 

 left in the state of a carbonate. 



When hot pyroxylic spirit is saturated with barytes, it de- 

 posits on cooling, silky needles, which speedily become 

 brown when exposed to the air. 



Pyroxylic spirit dissolves salts almost like alcohol. It pre- 

 cipitates the sulphates from aqueous solutions. It dissolves 

 chloride of calcium in abundance, and forms with it a cry- 

 stallizable compound. 



It dissolves the resins, and as it is more volatile than alco- 

 hol, it answers exceedingly well for making varnishes. It is 

 not so good a solvent of very hydrogenous bodies as alcohol; 

 but it is an excellent solvent of bodies which contain much 

 oxygen. 



When a mixture of 1 part of pyroxylic spirit, and 4 parts 

 of concentrated sulphuric acid is distilled, a gas comes over, 

 which possesses exactly the constitution of alcohol vapour. 



, It has an sethereal smell, is totally soluble in water, and 

 burns with a flame similar to that of alcohol. At first it is 

 mixed with carbonic acid gas, and sulphurous acid gas; but 

 if it be left for 24 hours in contact with fragments of potash, 

 these impurities are dissolved. The specific gravity of this 

 gas, as determined by MM. Dumas and Peligot, is 1-61 7. 



A volume of it requires for complete combustion JJ volumes 

 of oxygen gas, and forms 2 volumes of carbonic acid. Hence 

 it contains 



2 volumes carbon 0*8333 > condensed into 



2 volumes hydrogen 0-1388 J 1 volume. 



0-9722 

 If we subtract 0-9722 from 1-617, the specific gravity of the 

 gas, the remainder 0-6248 is almost exactly equal to the spe- 

 cific gravity of a volume of vapour of water, namely, 0*625. 

 Hence it is obvious that this vapour is a compound of 



1 volume olefiant gas... 0*9722 

 1 volume vapour of water 0*625 



1*5972 

 condensed into 1 volume ; which gives precisely the elements 

 that enter into the constitution of alcohol. 



The very same thing takes place in this distillation as when 

 we heat a mixture of alcohol and sulphuric acid. One half 

 the water is abstracted relative to the other ingredient, the 

 carbohydrogen. When alcohol is used, the deutocarbohy- 

 drogen, or olefiant gas, is converted into aether ; but when 



