Inorganic Constituents of Plants. 611 



the precipitated silver-salt ; for their quantitative estimation, 

 however, a larger portion of ash must be employed. 



6. Estimation of the Carbonic Acid. — The quantity of car- 

 bonic acid is represented by the loss sustained on treatment 

 of a known weight of ash with an acid; and we have else- 

 where described the most convenient method and apparatus 

 for the experiment. 



B. Analysis of Ashes abounditig in Silica, 



Ashes of this kind, as we have already observed, are generally 

 only partially soluble in acids; their alkalies must therefore be 

 determined in a separate portion of ash. The chlorine and 

 carbonic acid are determined in the same manner as when the 

 ash is entirely soluble in acids. The quantity of chlorine 

 found in ashes of this class is however probably always some- 

 what less than it should be, since the alkaline chlorides, when 

 ignited with silica and carbon, undergo a partial decomposition. 



1. Estimation of the Silica, Sfc. — Pure potash or soda ley is 

 poured upon about 4 grammes of the ash and evaporated to 

 dryness in a platinum or silver dish. The silicic acid com- 

 pounds are by this treatment dissolved, leaving the sand un- 

 affected. The heat should not be so great as to fuse the msss, 

 or some of the charcoal will be oxidated at the expense of the 

 water of the hydrated alkali. Dilute hydrochloric acid is 

 poured upon the mass, the whole evaporated, and the silica, 

 charcoal, &c, determined in the manner already described. The 

 acidulous solution filtered from the insoluble matter is divided 

 into two parts; one is employed for the determination of the 

 sulphuric and phosphoric acids, and the other for that of the 

 peroxide of iron and the alkaline earths, by the methods de- 

 tailed above. 



2, Estimation of the Alkalies. — A second portion of ash (say 

 3 grammes) is ignited in a crucible of platinum or silver with 

 four times its weight of hydrated barytes, the acid solution 

 which remains after separating the silica, &c. is precipitated 

 successively with barytes water, and carbonate of ammonia, 

 the alkalies being dien obtained in the state of chlorides. 



C. Determination of the Qiiantity of Ash. 



It is often important, even indispensable, to ascertain the en- 

 tire quantity of inorganic constituents contained in a plant or 

 part of a plant. A certain quantity of fixed matter is annually 

 removed from cultivated land in the crop, and it is a deside- 

 ratum to have a scale for the reparation of this loss by means of 

 manures. The chemist who is engaged with ash-analysis should 

 therefore acquire information as to the quantity which will be 



