Dr. T. Thomson on Pyroxylic Spirit and its Compounds. 45 



Pyroxylic spirit may be preserved without alteration in a 

 vessel, though imperfectly corked. But when its vapour 

 mixed with air is left in contact with spongy platinum, much 

 heat is evolved, and formic acid is formed. 



To make this experiment with ease, let a glass cylindrical 

 jar, open at both ends, be placed upon a large plate contain- 

 ing distilled water. Put 3 or 4- capsules, containing from 200 

 to 300 grains of spongy platinum within the jar, and also 

 some pyroxylic spirit in a wine glass, and within the glass jar. 

 By degrees the vapour of the pyroxylic spirit diffuses itself 

 through the glass jar, and the reaction commences whenever 

 a mixture of this vapour and air comes in contact with the 

 spongy platinum. Abundance of vapours condense on the 

 sides of the glass, which trickle down into the water, and give 

 it an acid taste. If the pyroxylic spirit be renewed in pro- 

 portion as it evaporates, the liquid in a few days contains 

 enough of acid to enable us to ascertain that it is impregnated 

 with Jbrmic acid. When alcohol is treated in the same way, 

 acetic acid is formed. 



What happens in this case will be understood by inspecting 

 the following formulaj: 



2 atoms of pyroxylic spirit are C" H'^ O^ 



1 atom of formic acid C"^ H O^ 



Hence, to convert 2 atoms of pyroxylic spirit into 1 atom of 

 formic acid, we must abstract 3 atoms of hydrogen, and add 

 1 atom of oxygen. The oxygen of the atmosphere, by the 

 intervention of the spongy platinum, converts 3 atoms of hy- 

 drogen into water, and adds 1 atom of oxygen. 



If we let the pyroxylic spirit fall, drop by drop, on the 

 spongy platinum, it becomes incandescent, and the spirit 

 burns, producing carbonic acid in great quantity. 



Chlorine acts upon pyroxylic spirit much less violently 

 than upon alcohol. When it is poured into a phial of dry 

 chlorine gas, hardly any heat is evolved, and the action is 

 slow, even when assisted by the solar influence. Even when 

 chlorine and pyroxylic spirit are agitated together, the action 

 is very slow. It it necessary to distil the liquid a number of 

 times in contact with chlorine. Two liquids a reproduced ver\f 

 different in their volatility. The least volatile combines with 

 ammonia, and forms a crystallizable compound. 



But Mr. Kane found, that when dry chlorine gas and 

 vapour of jiyroxylic spirit come in contact, an explosion 

 takes place. He passed a current of chlorine through the 

 spirit to saturation. Much muriatic acid was formed. He 

 obtained two liquids. The lightest was very acid. The 

 other was thick, had nearly the specific gravity of sulphuric 



