6lO AGRICULTURAL ANALYSIS 



acid and potash, but also for a complete analysis of an ash in so 

 far as its usual constituents are concerned. 



518. Carbon, Sand, and Silica. The earlier official agricultural 

 methods prescribe the following procedure for the determina- 

 tion of the unburned carbon, and the sand and silica: 85 



Five grams of the ash are treated in a beaker, covered with a 

 watch-glass with 50 cubic centimeters of hydrochloric acid of 

 1.115 specific gravity, and digested on the water bath until all 

 effervescence has ceased. The cover is removed and the liquid 

 evaporated to complete dryness to render the silica insoluble. 

 The residue is moistened with two or three cubic centimeters of 

 hydrochloric acid and taken up with about 50 cubic centimeters 

 of water, allowed to stand on the water bath a few minutes, 

 filtered, and thoroughly washed. The filtrate and washings are 

 made up to a quarter of a liter for analysis. The residue is 

 washed from the filter into a platinum dish and boiled about 

 five minutes with 20 cubic centimeters of a saturated solution 

 of pure sodium carbonate ; afterwards a few drops of pure 

 sodium hydroxid solution are added and the liquid allowed to 

 settle, and it is then decanted through a tared gooch. The residue 

 is boiled with sodium carbonate solution and decanted as before, 

 a second and a third time, and finally brought upon the felt and 

 thoroughly washed, first with hot water, then with a little dilute 

 hydrochloric acid, and finally with hot water until free of chlo- 

 rids. The residue in the gooch is dried at no to constant 

 weight, giving the carbon and sand. It is then incinerated and 

 the weight of the sand determined, the difference giving the 

 carbon. It is advisable to examine the sand with a microscope 

 to determine if it be pure. The alkaline filtrate and washings 

 from the carbon and sand are acidified with hydrochloric, evap- 

 orated to dryness, and the silica separated and determined in 

 the usual way. 



Instead of determining soluble silica directly from the sodium 

 carbonate solution, as above, another portion of the ash may be 

 treated with hydrochloric acid and evaporated to dryness as be- 

 fore described, filtered on an ordinary filter, washed, burned. 

 85 Division of Chemistry, Bulletin 43, 1894 : 390. 



