DETERMINATION OF INORGANIC PLANT CONSTITUENTS 619 



with sodium carbonate solution and decanted as before, and the 

 process repeated a third time, after which the residue is brought 

 upon the filter and thoroughly washed, first with hot water, then 

 with a little dilute hydrochloric acid, and finally with hot water 

 until free from chlorids. The gooch and contents are dried to 

 constant weight at no", and the combined weight of carbon and 

 sand determined. After incineration the loss in weight gives the 

 carbon. It is advisable to examine the residue under the micro- 

 scope to ascertain if it is really sand. The alkaline filtrates and 

 washings are to be united, acidified with hydrochloric acid, 

 evaporated to dryness, and the silica separated and determined 

 in the usual way. 



Alternate Method. Instead of determining directly the 

 silica dissolved by the sodium carbonate solution, as described 

 above, another portion of the ash may be treated as in 2(0} and 

 (rf), and the residue of silica, sand, and carbon filtered on an or- 

 dinary filter, washed, burned, and weighed, giving the combined 

 weight of silica and sand, from which the weight of sand found in 

 2(d) is to be deducted to obtain the silica. It is inadmissable to 

 separate the soluble silica from the residue after ignition. 



Subtract carbon, carbon dioxid, and calcium oxid added in the 

 form of calcium acetate from the ash, and calculate results as 

 carbon-free ash. 



3. Determination of Manganese, Calcium, and Magnesium. 

 To an aliquot of solution A, corresponding to from 0.5 to two 

 grams of ash, add a quantity of pure ferric chlorid solution, more 

 than equivalent to the phosphoric acid which may be present, 

 neutralize with ammonia, dissolve the precipitate in a very slight 

 excess of hydrochloric acid, add one or two grams of sodium 

 acetate and boil one or two minutes, filter at once and wash with 

 boiling water. If necessary, dissolve the precipitate in hydro- 

 chloric acid and reprecipitate as above. Evaporate the filtrate 

 and washings to about 50 cubic centimeters and determine man- 

 ganese, calcium, and magnesium as in the analysis of soils. 90 

 The quantity of calcium found must be corrected for the calcium 

 .added. 



90 Bureau of Chemistry, Bulletin 107, 1904 : 15, (c), (d), (e). 



