186 PHOSPHORUS and phosphoric acid. 



vegetable matter is undergoing denaj' in the presence of water contain- 

 ing gypsum, or other sulphates ; and it may occasionally be detected by 

 the sense of smell among the roots of the sod, in old pasture land, lo 

 which a top-dressing is occasionally given. 



As in the egg, so also in other decaying animal substances, especially 

 when the air is in some measure excluded, this gas is formed. In pu- 

 trified cow's urine, and in night soil, it is present in considerable quan- 

 tity. 



Sulphuretted hydrogen is exceedingly noxious to animal and vegeta- 

 ble life, when diffused in any considerable quantity through the air by 

 which they are surrounded. The luxuriance of the vegetation in the 

 neighbourhood of sulphurous springs, however, has given reason to be- 

 lieve that water impregnated with this gas, may act in a beneficial 

 manner when it is placed within reach of the roots of plants. It seems 

 also to be ascertained that natural or artificial waters which have a sul- 

 phurous taste, give birth to a peculiarly luxuriant vegetation, when they 

 are employed in the irrigation of meadows. — [Sprengel, Chemie^ I., 

 p. 355.] 



The relative constitution of these three compounds of sulphur is thus 

 represented : — 



Is repre- Or 1 of Sulphur 



One equivalent of Weighing seated by and 



Sulphur 16 S 



Sulphurous Acid . . 32 SOg 2 of Oxygen 



Sulphuric Acid ... 40 SO3 3 of Oxygen 



Sulphuretted Hydrogen 17 SH 1 of Hydrogen.* 



IV. PHOSPHORUS AND PHOSPHORIC ACID. 



1°. Phosphorus is a solid substance of a pale yellow colour, and of a 

 consistence resembling that of wax. When exposed to the air it slowly 

 combines with the oxygen of the atmos[)here, and burns away with a 

 pale blue flame visible only in the dark. When rubbed, however, or 

 exposed to a slight elevation of temperature, even to the heat of the 

 hand, it readily bursts into a brilliant flame, emitting an intense light 

 accompanied by dense white vapours. It does not occur in nature in 

 an uncombined state, and is not known to be susceptible of any useful 

 application in practical agriculture. 



2°. Phosphoric Acid. — The white fumes given off by phosphorus, or 

 rather into which it is changed, when burned in the air or in oxygen 

 gas, consist of phosphoric acid. This compound is solid and colourless, 

 attracts moisture from the air with great rapidity, is exceedingly soluble 

 in water, has an intensely sour taste, and like sulphuric acid is capable 

 of corroding and destroying animal and vegetable substances. 



It does not exist in nature in a free state, and, therefore, is not directly 

 influential upon vegetation. It unites, however, with potash, soda, lime, 

 &;c., to form compounds, known by the name o^ phosphates. In these 

 states of combination, it is almost universally diffused throughout nature 

 — and appears to be essentially necessary to the healthy growth and 

 maturity of all living — certainly of all cultivated vegetables. 



* For the properties of oxygen and hydrogen see above, pages 34 and 25, and for their 

 equivalent or atomic weights see page 3i 



