228 WALL'S MANUAL 



upon them freely, rub the extremities, and, if the 

 body is cold, administer a warm bath. 



Carbonic acid is used to suffocate insects, as butter- 

 flies, when it is desired to preserve the colors perfect. 

 The Lake of Averno, which was asserted by the 

 ancients to have been the entrance to the infernal 

 regions, evolves so large a quantity of carbonic acid 

 gas, that birds flying over it drop from suffocation. 

 Carbonic acid unites with bases forming a class of 

 salts the carbonates. 



Sulphuric Acid. This powerful acid is of the 

 greatest interest to the chemist, agriculturist and 

 manufacturer. It was formerly obtained from " green 

 vitriol," and hence called " oil of vitriol" It is now 

 prepared upon a large scale, by heating sulphur and 

 nitre in furnaces and conducting the sulphurous and 

 nitrous acid fumes which" are thus formed, into vast 

 leaden chambers, along with steam and atmospheric 

 air, the floor of the chamber being covered with 

 water. The water at the bottom of the chamber, 

 which soon becomes very acid, is draw r n off and 

 boiled down in platinum stills to a sufficient degree of 

 concentration. 



When the acid is procured from the distillation of 

 green vitriol, it comes off in a dry state, and attracts 

 moisture so rapidly as to cause fuming ; it is hence 

 called the fuming oil of vitriol or " Nordhousen acid," 

 because it was largely manufactured in a city of that 

 name in Saxony. Common sulphuric acid or oil of 

 vitriol, contains a larger proportion of water. 



Properties. Sulphuric acid has a thick, oily appear- 

 ance, with a greasy or soapy face; but it speedily 

 corrodes the skin, and causes an intense burning 



