SULPHUROUS ACID. 167 



sulphuric acid, and fifty cubic inches of water, when 

 mixed, do not fill a vessel of the capacity of one hun- 

 dred cubic inches, but fall about three inches short. 

 Condensation has, therefore, taken place to the amount 

 of three inches. Heat is, as it were, pressed out in 

 such cases, as explained in the early part of this work. 



404. WOOD CHARRED BY SULPHURIC 



Why does sul- 

 phuric acid ACID. Wood dipped in oil of vitriol is 



soon charred. Wood is composed of car- 

 bon, hydrogen, and oxygen. The last two together 

 form water. The affinity of sulphuric acid for water has 

 been mentioned above. The acid and the wood being 

 in contact, it would seem that the hydrogen and the 

 oxygen of the latter agree to combine and satisfy this 

 demand. The carbon being at the same time isolated, 

 appears in its natural black color. Sulphuric acid ex- 

 erts a similar action on other vegetable substances. 



405. IMPORTANT USES. Sulphuric acid 



What are the . 



uses of sul- is largely employed for dissolving indigo, 

 pkuric add? for use in dyeing and calico p r i nt i n g . a i so? 



for converting common salt into sulphate of soda, as a 

 preparatory step to the manufacture of carbonate of 

 soda. It is also essential in the manufacture of super- 

 phosphate of lime, an article now so extensively used 

 in agriculture. Nitric and muriatic acids are pro- 

 duced through its agency from nitre and common 

 salt. 



SULPHUROUS ACID. 



What is sul- 406. DESCRIPTION. Sulphurous acid is 

 phurous acid? a gaSj having the smell of a burning match. 



