50 SCIENTIFIC AGRICULTURE. 



generally. They are divided into fixed and volatile, the 

 fixed alkalies are potash and soda: these do not evaporate, like 

 ammonia, which is therefore called a volatile alkali. They 

 have a sharp, pungent taste, destitute of acidity, and, with the 

 exception of ammonia, have but little odor. They unite with 

 the oils and fats, and form the well known compound, soap. 

 There is also a class of compounds called alkaline earths, as 

 lime, barytes, magnesia and strontium. The alkalies and alka- 

 line earths are electro-positive in their affinities. 



SALTS. 



Salts constitute a numerous class of compounds, which 

 result from the chemical union of acids and alkalies. They 

 are of three kinds, viz : acid, basic and neutral. 



Acid salts contain an excess of acid ; most of them are not 

 really acid salts, but double salts, of which one base is water ; 

 bi-carbonate of potash is an example. [Kane.] The sub- 

 stance which unites with an acid to form a salt, is called a 

 lase, 



Basic salts are those in whicli there is more than one 

 equivalent of base for one of acid, as in sulphate and nitrate 

 of copper. 



Neutral salts do not manifest either acid or alkaline proper- 

 ties on vegetable colors, they have neither an acid nor an 

 alkaline taste, and generally consist of one equivalent of acid 

 and one of base. 



Double salts are formed by the union of two simple salts; 

 in general both salts contain the same acid, but different bases. 

 Salts usually crystalize in regular determinate forms; some 

 being in prisms or crystals, having three, four, five, six, 

 &c., sides, and as many angles. Most salts contain some 

 water in a loose state of combination : this is called their water 

 of crystalization. This water evaporates from some salts, and 

 they become a dry powder, such are called effervescent salts: 



