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 asmall 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, 
in 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 O2, H,O, as a gritty 
powder. : 
Inthe 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, on element which has many analogies with silicon, 
though rarely occurring in large quantities, is yet often present in the 
form of Titanie acid, Ti Os, 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. 
Arxatt-Metats.—The elements Potassium, Sodium, 
(Lithium, Rubidium, and Caesium), are termed alkali- 
