44 PRACTICAL FARM CHEMISTRY. 



matcli contains a small quantity of phosphorus. A 

 slight scratch, or the sole of your boot placed upon 

 it on the barn floor, or the mere nibbling of a mouse 

 or rat, is sufficient to provoke the atom of phospho- 

 rus to unite with the oxygen of the air; thus, in one 

 case, giving you the means to light your pipe or the 

 kindling in the stove, or, in the other case, setting 

 barn or house on fire. The product of the union of 

 the two elements is a cloud of dense, whitish fumes, 

 and consists of the often-mentioned, all-important 

 plant food, phosphoric acid. 



We need not concern ourselves about the charac- 

 teristic features of this simple compound, its corro- 

 siveness, sour taste, its solubility in water, etc., for 

 we find it in plant and animal structure only in 

 combinations with lime, soda, potash and other 

 bases, and in these forms fortunately for us, it is 

 universally diffused, and very plentiful in nature. 



Phosphate of lime is by far the most important 

 and the most common of these combinations; and 

 we find it in inexhaustible natural deposits as apa- 

 tite, or mineral phosphate of lime; in the remains of 

 animals; in phosphatic guanos (leached 

 **"^ * * dung of sea fowls), etc. South Caro- 

 lina and Florida furnish vast quantities of phosphate 

 rock. More than one half of the dry substance of 

 animal and human bones consists of phosphate of 

 lime, and nearly one half of the latter consists of 

 phosphoric acid. Flesh and other animal tissues 

 have also some phosphate of lime, and each one 

 hundred pounds of dried bones contain about 

 twenty-eight pounds of phosphoric acid. 



In animal manures, epecially in the liquid void- 

 ings of living creatures, we find another and more 

 concentrated form of phosphoric acid — a double 



