6l8 AGRICULTURAL ANALYSIS 



usual way. The calcium is then precipitated with ammonia and 

 ammonium oxalate in hot solution, the precipitate washed well, 

 dried, ignited and weighed. It is then dissolved and diluted 

 so that 100 cubic centimeters contain i.i grams calcium oxid. 



It is best to test the purity of this reagent by making blank 

 determinations with it. 



(b) Preparation of Ash. Moisten from 10 to 20 grams of the 

 substance with 40 cubic centimeters of calcium acetate solution, 

 dry on a water bath, and ignite, gently at first, then more vigor- 

 ously. 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 or Tucker's, 

 or an ordinary platinum dish may be ir,ed, fitted with a cover, like 

 that described by Wislicenus. The weight of the ash must be 

 corrected for lime, carbon dioxid and carbon. 



(c) Determination of Carbon Dioxid. Using the ash prepared 

 in (b), 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. 



(d) Determination of Carbon, Sand and Silica. The residue 

 from the carbon dioxid determination is transferred to a beaker 

 or evaporating dish, evaporated to dryness and thoroughly dried 

 and pulverized to render silica insoluble. The dry residue is 

 moistened with from five to 10 cubic centimeters of hydrochloric 

 acid, taken up with about 50 cubic centimeters of water, allowed 

 to stand on the water bath for a few minutes, filtered through a 

 parchment-paper filter (S. and S. "hardened" filters), and thor- 

 oughly washed. The solution and washings are to be made up to 

 250 cubic centimeters or other convenient volume and preserved 

 for analysis. This is solution A. 



The residue is washed from the filter (which may 

 be used again) into a platinum dish and boiled about 

 five minutes with 20 cubic centimeters of a saturated solution 

 of pure sodium carbonate, a few drops of pure sodium hydroxid 

 solution are added, the solids are allowed to settle, and the liquor 

 decanted through a tared gooch. The residue in the dish is boiled 



