THE ASH OF PLANTS. 123 



heat of 212 or more, appear, to be totally insoluble in pure 

 water. 



All the hydrates of silica are readily soluble in solutions 

 of the alkalies and alkali carbonates, and readily unite 

 with moist, slaked lime, forming silicates. 



EXP. 58. Gelatinous Silica. Pour a small portion of the solution of 

 silicate of potash of Exp. 56, into strong chlorhydric acid. Gelatinous 

 silica separates and falls to the bottom, or the whole liquid becomes a 

 transparent jelly. 



EXP. 59. Conversion of soluble into insoluble hydrated silica. Evaporate 

 the solution of silica of Exp. 57, which contains free chlorhydric acid, 

 iu a porcelain dish. As it becomes concentrated, it is very likely to ge- 

 latinize, as happened in Exp. 58, on account of the removal of the sol- 

 vent. Evaporate to perfect dryness, finally on a water-bath (i. e. on a 

 vessel of boiling water which is covered by the dish containing the solu- 

 tion). Add to the residue water, which dissolves away the chloride of 

 potassium, and leaves insoluble hydrated silica, 3 Si O 2 , H 2 O, as a gritty 

 powder. 



In the ash of plants, silica is usually found in combination 

 with alkalies or lime, owing to the high temperature to 

 which it has been subjected. 



In the plant, however, it exists chiefly, if not entirely, 

 in the free state. 



Titanium, an element which has many analogies with silicon, 

 though rarely occurring in large quantities, is yet often present in the 

 form of Titanic acid, Ti O 2 , in rocks and soils, and according to Salm 

 Horstmar may exist in the ashes of barley and oats. 



Arsenic, in minute quantity, has been found by Davy in turnips 

 which had been manured with a fertilizer (superphosphate), in whose 

 preparation, oil of vitriol, containing this substance, was employed. 



The metallic elements which remain to be noticed, viz. : 

 Potassium, Sodium, Calcium, Magnesium, Iron, Manga- 

 nese, (Lithium, Rubidium, Caesium, Aluminum, Zinc, 

 and Copper,) are basic in their character, i. e., they unite 

 with the acid bodies that have just been described to 

 produce salts. Each one is, in this sense, the base of a 

 series of saline compounds. 



ALKALI-METALS. The elements Potassium, Sodium, 

 (Lithium, Rubidium, and Caesium), are termed alkali- 



