AZOTIC GAS. 101 



has the property of combining with the various 

 bases, and of forming salts distinguished by the 

 generic name of nitrates. Several of these nitrates 

 contain no water of crystallization, but consist of 

 the anhydrous acid united to the base ; this is 

 the case with nitrate of lead and nitrate of po- 

 tash, I shall make use of nitrate of lead to de- 

 termine the atomic weight of nitric acid. 



It will be shown in a subsequent chapter, that From ni - 

 the atom of lead weighs 13, and the atom of pro- 

 toxide of lead, which constitutes the base of ni- 

 trate of lead, 14. This salt is neutral, and con- 

 sequently consists of one atom of nitric acid uni- 

 ted to one atom of protoxide of lead. It is white, 

 opaque, has a strong lustre, and crystallizes in 

 octahedrons. Sometimes it may contain a little 

 water mechanically lodged between its plates ; 

 but this is not the case when it is properly crys- 

 tallized ; and it may be always rendered anhy- 

 drous by exposure for a few hours to a heat of 



Sulphate of soda is a salt composed of one 

 atom sulphuric acid, one atom soda, and ten 

 atoms water : but it is with great facility freed 

 from its water of crystallization. A few days' 

 exposure in a dry room is sufficient for the pur- 

 pose ; or we may place it in the vacuum of an 

 air-pump, in a vessel raised an inch or two above 

 a flat plate filled with sulphuric acid. Twenty- 

 four hours of such a situation renders it quite 



G2 



