38 ELEMENTARY AGRICULTURAL CHEMISTRY 



sulphuretted hydrogen being produced from bye-products in 

 the manufacture of " soda ash " (sodium carbonate) from 

 common salt. 



Sulphur (" brimstone ") is a yellow, brittle substance which 

 is very inflammable. It burns in air with a pale blue flame 

 and forms the suflTocating gas, sulphur dioxide, SOg^ while' small 

 quantities of sulphur trioxide, SO3, are also produced. The 

 latter by its union with the water vapour always present in 

 the air, forms sulphuric acid, HgSO^. Sulphur, like carbon, is 

 capable of existing in three modifications, possessing difierent 

 physical properties. Unoxidised or partially oxidised sulphur 

 compounds are very injurious to plants, while sulphates are 

 not only harmless, but necessary. Sulphur is present in the 

 albuminoids of both animals and plants, and when putrefaction 

 of these substances occurs is often liberated as sulphuretted 

 hydrogen. This substance is perceptible by its disagreeable 

 odour as one of the chief products of the decay of albumin in 



Phosphorus always occurs in a state of combination. 

 Phosphorus compounds, chiefly phosphates, are very widely 

 distributed, but in small proportion, in the rocks of the earth. 

 Deposits of calcium phosphate, Ca3P208, occur in certain 

 localities, and are highly iprbwA for manurial purposes. All 

 fertile soils contain small quantities of phosphates, which are 

 taken up by plants, and through plants find their way into 

 animals, where they accumulate in the bones or other hard- 

 parts {e.g., teeth and shells). The element itself is somewhat 

 difficult to obtain, because of its strong affinity for oxygen. It 

 is prepared by the action of carbon upon metaphosphoric acid 

 at a very high temperature, the chief reaction being — 



4HP03 + 12C = 12CO + 2H, + P,. 



Phosphorus, as usually prepared, is a yellowish, waxy 

 substance which has the power of emitting a faint light when 

 exposed to air. This property was the origin of its name, 



