168 BIOLOGY OF PLANTS. 



a large class of salts. It is usual, however, to call the com- 

 pounds of silicic acid with'bases, silicates, and the compounds of 

 other acids with the same bases, salts. 



Hydrochloric acid is composed of one equivalent of chlorine, 

 35.42, and one of hydrogen, 1=36.42. (HCl.) This acid, in 

 its pure state, has very acrid and caustic properties. It is com- 

 , monly called muriatic acid, because obtained from sea salt. Its 

 ^^i>>y"U)Jsprinciple^• salt is hydrochlorate of anmionia, known as sal am- 

 moniac. 



Sulphuric acid, a compound of sixteen parts of sulphur and 

 forty of oxygen, is an oily liquid well known as oil of vitriol. 



Phosphoric acid is composed of two equivalents of pliospho- 

 rus, 31.4, and 5 of oxygen, 40=71.4 (symbol P^QS). This 

 acid resembles snow or ice. It is intensely sour, and com- 

 bines with a number of alkalies and alkaline earths, forming a 

 class of salts called phosphates. Phosphate of lime is the prin- 

 cipal substance in the bones of animals. 

 . JVitjic acid has been described, p. 48. 



Is morphisnf IS a term used to designate the fact, that bodies of 

 very different chemical constitution, may assume the same crys- 

 talline form, and may displace each other in any compound. 

 When this is the case, that is, when one body is substituted, for 

 another, there is not an equal, but an equivalent proportion ; 

 thus, when soda is substituted for potassa, thirty-one parts of 

 the former take the place of forty-seven of the latter. 



As plants uniformly contain several inorganic bodies, we 

 infer, that these substances are necessary for the formation of* 

 particular organs. For although the inorganic constituents 

 of plants may vary according to the soil in which the plant 

 grows, a certain number of them is absolutely essential to its 

 development. The principal of these inorganic substances 

 are potash, soda, magnesia, lime, alumina, and oxides of iron 

 and of manganese, which are the inorganic bases, and are 

 generally combined with silicic, hydrochloric, sulphuric, phos- 

 phoric, carbonic and nitric acids. 



The inorganic bases of plants vary with the nature of the 

 soil. DeSaussure and Berthier found magnesia in the ashes 

 of a pine tree, growing at Mont Breven, but none in the ashes 



