224 SOILS. 



plies also to the phosphates. Or a large quantity of 

 water may be evaporated to a small bulk, mixed with 

 ammonia, the precipitate filtered off, dissolved in nitric 

 acid, and tested for phosphoric acid with molybdate 

 of ammonia. 



XVIII. Arsenic acid, in combination with lime or 

 sesquioxide of iron, must likewise be sought, in the 

 stalactites or ochres from such waters, with the aid of 

 Marsh's apparatus. (See Poisoning by Arsenic.) 



XIX. Antimony and copper, to be tested for in the 

 deposit, by sulphuretted hydrogen. 



XX. Fluorine, also contained in the deposit as 

 fluoride of calcium. Or it may be sought in the pre- 

 cipitate obtained by ammonia in XVIL, a part of 

 which should be dried and moistened with concentrated 

 sulphuric acid in a platinum crucible covered with a 

 glass-plate coated with wax and marked in order to 

 test for fluorine. (See No. 82.) 



117. SOILS. 



The ordinary constituents of soils, which differ 

 much in different soils, and are very variable in quan- 

 tity, are salts of chlorine, sulphuric acid, phosphoric 

 acid, silicic acid, carbonic acid, nitric acid, with potassa, 

 soda, ammonia, lime, magnesia, alumina, protoxide 

 of manganese and protoxide of iron, together with 

 sand and organic matters consisting of the debris of 

 plants, and of the humous substances produced by 

 their decay. 



Some of these constituents are soluble in water. 



Others are insoluble in water, but soluble in dilute 

 acids, as, for example, the carbonates and phosphates 

 of lime and magnesia. 



The remainder are insoluble even in dilute acids; 



