Inorganic ConstiUients of Plants. fiOT 



most cases complete, unless the ash be obtained from the stems 

 of the grasses, which abound in silicic acid. 



After the separation of the silica, the acid solution is treated 

 with acetate of ammonia, or it may be neutralized by means 

 of caustic ammonia, free acetic acid being then added ; in most 

 cases a yellowish-white gelatinous precipitate is formed, which 

 consists of phosphate of the peroxide of iron. This precipi- 

 tate is collected upon a filter, and ammonia is added in excess 

 to the clear solution, by which a fresh precipitation will ge- 

 nerally be occasioned. If a red precipitate be formed, it is 

 peroxide of iron ; if, after standing some time excluded from 

 the air, no precipitation takes place, we conclude that the ash 

 contains no phosphate besides the one previously separated ; 

 but if a white precipitate be formed (phosphate of lime and 

 phosphate of magnesia), it is known that there is more phos- 

 phoric acid present than is required to combine with the per- 

 oxide of iron. Nothing further is necessary for the completion 

 of the qualitative analysis, but to test for fluorine and oxide of 

 manganese, and, in the case of marine plants, for iodine and 

 bromine ; unless, indeed, it happen that the experimenter have 

 reason to suspect the presence of other substances in the ash. 



For the determination of the chlorine (iodine and bromine) 

 and of the carbonic acid, separate portions of ash are always 

 employed, as also for that of the alkalies, in ashes belonging 

 to the third group. All the other constituents are determined 

 in one quantity of ash, so that the silica has only to be sepa- 

 rated once. 



A. Analysis cf Ashes rich in Carhonates and Phosphates. 



1. Determination of the Silica of the Charcoal and of the 

 Sand. — About 4 grammes of the ash, which has been found to 

 be soluble in hydrochloric acid, is treated with the concen- 

 trated acid in a matrass, held obliquely, so as to avoid the 

 loss of fluid during the evolution of carbonic acid; gentle heat 

 is then applied, until it is evident that everything is dissolved, 

 excepting the carbonaceous and sandy particles. The whole is 

 row carefully removed into a porcelain basin, evaporated to 

 dryness over a water-bath, and then heated somewhat more 

 strongly, as is usual in separating silica. The mass when 

 cold is moistened witli strong hydrochloric acid, is digested for 

 Ijalf an hour with a sufficient quantity of water, and is boiled, 

 after which the acid liquid is poured upon a stout filter which 

 has been previously dried at JOO"^ C. and weighed. 



The silica will remain upon the filter, and if the ash was 

 not perfectly white and pure, some sand and charcoal also. 

 The filter is washed and dried, and the substance carefully 

 removed from it into a platinum crucible without injury to the 



2 L2 



