THE ASH OP PLANTS. 135 



the sturgeon of the Caspian Sea. It is also an ingredient 

 of guanos, and probably of animal excrements in general. 

 The tricalcic phosphate, or, as it is sometimes termed, 

 the bone-phosphate, 3 CaO, P 2 O 5 , is a chief ingredient of 

 the bones of animals, and constitutes 90 to 95 per cent of 

 the ash or earth of bones. It may be formed by adding a 

 solution of lime to one of phosphate of soda, and appears 

 as a white precipitate. It is insoluble in pure water, but 

 dissolves in acids and in solutions of many salts. In the 

 mineral kingdom tricalcic phosphate is the chief ingredient 

 of apatite and phosphorite. These minerals are employed 

 in the preparation of the so-called superphosphate of lime, 

 which is consumed to an enormous extent as a turnip-fer- 

 tilizer. The superphosphate of commerce, when genuine, 

 is essentially a mixture of sulphate of lime with the three 

 phosphates above noticed, of which the monocalcic phos- 

 phate should predominate. 



The Phosphates of Magnesia, Iron, and Manganese, 

 are bodies insoluble in water, and require no particular 

 notice. 



THE CHLOBIDES are all characterized by their ready solu- 

 bility in water. The chlorides of Lithium, Calcium, and 

 Magnesium, are deliquescent, i. e., they liquefy by absorb- 

 ing moisture from the air. The chlorides of Potassium 

 and Sodium alone need to be described. 



Chloride of Potassium, K Cl, 74.5. This body may be 

 produced either by exposing metallic potassium to chlorine 

 gas, in which case the two elements unite together direct- 

 ly ; or by dissolving caustic potash in chlorhydric acid. 

 In the latter case water is also formed, as is expressed by 

 the equation K HO + H Cl = K Cl + H 2 O. 



Chloride of potassium closely resembles common salt 

 (chloride of sodium) in appearance, solubility in water, 

 taste, etc. It is but rarely an article of commerce, but is 

 present in the ash and in the juices of plants, especially of 

 sea-weeds, and is likewise found in all fertile soils. 



