Dr. T. Thomson on Fyroxrjlic Spirit and its Compounds. 87 



trated sulphuric acid. As soon as ebulUtion commences there 

 passes into the receiver an oily liquid, mixed with a methvlic 

 liquor. This oily liquid becomes gradually very abundant, 

 and when the distillation is finished, its quantity is at least 

 equal to that of the pyroxylic spirit employed. The acid 

 mixture should be distilled slowly, but the boiling should be 

 constantly kept up. 



This oily liquid being separated by decantation from the 

 a(|ueous liquor, is first agitated with a little water, and then 

 with a little chloride of calcium. It is then rectified several 

 times successively over caustic barytes in a very fine powder. 

 Finally, it is proper to leave it for some time in the vacuum 

 of an air-pump with concentrated sulphuric acid and potash. 

 The object of these processes is to separate some sulphuric 

 acid, sulphurous acid, water, and pyroxylic spirit, which the 

 liquid may contain. 



When pure it is colourless, has an alliacious smell, and a 

 specific gravity of 1*324 at the temperature of 71^°. It boils 

 at the temperature of 370°, under a pressure of thirty inches 

 of mercury. 



Dumas and Peligot subjected it to analysis by means of 

 oxide of copper, and found 100 parts of it to yield 



Carbon 39-03 



Hydrogen 4;*78 



Now, these two numbers are to each other in the proportion 



of 2 atoms carbon = 1'5 



3 atoms hydrogen = 0*375 



If we consider it as composed of 



2 atoms carbon = 1*5 or per cent. 19*04? 



3 atoms hydrogen = 0*375 4*76 



1 atom oxygen = 1*000 — — 12*70 



1 atom sulphuric acid = 5*000 63*50 



7*875 100*00 



Then it consists obviously of 



C^ H'^ O + S O^ 

 If C^ H'^ O be methylene, it is a sulphate of methylene. 



Dumas and Peligot attempted to determine the density of 

 the vapour of sulphate of methylene. They obtained as a 

 result 4''565. But they do not consider this number as de- 

 serving of confidence. There can be little doubt that the 

 true specific gravity of the vapour of this substance is 4*3750, 

 for it obviously consists of 



1 volume methylene vapour 1*5972 



1 volume sulphuric acid 2*7777 



4*3750 



