III. METHODS FOR THE ANALYSIS OF INORGANIC PLANT 



CONSTITUENTS. 



(For provisional combustion method see Appendix, p. IT.*;. ) 

 1. Preparation of Sample. Official. 



Thoroughly cleanse the material from all foreign matter, especially from 

 adhering soil. Grind, and preserve the sample in carefully stoppered bottles. 



2. Carbon-Free Ash. Official, 

 (a) PREPARATION OF STANDARD CALCIUM ACETATE. 



(1) Dissolve 20 grams of chemically pure calcium carbonate in chemically 

 pure acetic acid and dilute to 1 liter. To standardize this evaporate 20 cc in 

 a platinum dish, ignite gently, then strongly, to constant weight. The dish 

 must be weighed quickly. This procedure gives the calcium oxid in 20 cc. 



(2) An alternative method is to dissolve marble in hydrochloric acid, evapo- 

 rate, and dry to render silica insoluble, dissolve with water and a little acid, 

 and precipitate iron and aluminum in the usual way. Then precipitate the 

 calcium with ammonium hydroxid and ammonium oxalate in hot solution, 

 wash well, dry, ignite, and weigh. Dissolve in acetic acid and dilute so that 

 100 cc contain 1.1 grams of calcium oxid. It is best to test the purity of this 

 reagent by making blank determinations. 



(b) PREPARATION OF ASH. 



(For optional official method without the use of calcium acetate see Appendix, 



p. 238.) 



Moisten 10 to 20 grams of substance with 40 cc of calcium acetate, dry on a 

 water bath, and ignite, gently at first, then more vigorously. The quantity of 

 calcium acetate used should be sufficient to prevent fusion of the ash. Some 

 form of apparatus must be used to prevent volatilization, either Shuttleworth's 6 

 or Tucker's , or an ordinary platinum dish may be used, fitted with a cover, 

 like that described by Wislicenus.<* The weight of the ash must be corrected 

 for lime, carbon dioxid, and carbon. 



(c) CARBON DIOXID. 



Using the ash prepared in (ft), liberate the carbon dioxid with hydrochloric 

 acid in any of the usual forms of apparatus, determining the carbon dioxid 

 evolved either by increase of weight of potash bulbs or loss of weight of the 

 apparatus. The former method is preferred. 



Neither provisional nor official methods for the determination of Iron and aluminum 

 have been adopted, but such determinations should be made. 

 *Exper. Stat. Rec., 11: 304. 

 Ibid., 506. 

 rf Zts. anal. Chem., 1901, 40: 441. 



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