96 PHOSPHORUS — PHOSPHORIC ACID. 



ride in sea-water, and the fluoride of calcium, which 

 exists in small quantity in the bones of animals. 



194. Phosphorus in several respects resembles sul- 

 phur ; like it, it is a readily fusible and very combus- 

 tible solid. It is of a white color, about as hard as 

 wax, and has so strong an affinity for oxygen that it 

 takes fire in the air with the greatest facility as soon 

 as it is a little warmed. Like the preceding element, 

 chlorine, it is never met with in a separate state, but 

 always in combination. Its most important compound 

 is phosphoric acid, the substance which is formed when 

 phosphorus burns in the air or in oxygen ; it is a white 

 solid substance, very soluble in water, and eagerly 

 combining with bases to form a class of salts called 

 phosphates (161, 242). 



195. Phosphoric acid is generally obtained by de- 

 composing one of its compounds by sulphuric acid. 

 The most abundant compound of phosphoric acid is 

 that in which it is united to lime, called the phosphate 

 of lime (242) : this substance is an ingredient of the 

 bones of animals, and of most organic substances. 

 When sulphuric acid is mixed with phosphate of lime, 

 the latter is decomposed, and its phosphoric acid is 

 set at liberty. The acid may be artificially made by 

 burning phosphorus in the air, from which it abstracts 

 the oxygen, and leaves the nitrogen unaltered ; just 

 in the same way that carbon when burnt in air, forms 

 carbonic acid: only that in this case the product of 

 combustion is a gas, like the air ; whilst the result 

 of the combustion of phosphorus, is a white solid 

 acid. 



