§ 99. THE CHEMICAL ANALYSIS. 175 



stoppered bottle, and pour over it 1500 c.c. of pure con- 

 centrated hydrochloric acid (Sj). Gr. = 1.15), and shake 

 the mixture frequently during a digestion of 48 liours, at 

 the common temperature of the working-room ; then let 

 it stand until 1000 c.c. of at least a tolerably clear liquid 

 can be poured oiF or drawn off with a siphon ; this quan- 

 tity of the solution represents ^\^oi 450 grms., or 300 

 grms. of the soil taken for the analysis ; dilute the liquid 

 with its volume of water, and filter it. 



If the soil contains a very large proportion of calcic 

 carbonate, the cold acid solution may be filtered off after 

 dilution with its volume of water, and the whole quan- 

 tity used for the analysis, representing the whole of the 

 soil taken ; in this case, wash the insoluble residue care- 

 fully first with cold and then with hot water, dry it at 

 100° C, and weigh, to deteimine the proportion of the 

 soil insoluble in cold acid; 5-10 grms. of this may be 

 ignited, to determine the organic matter in the insolu- 

 ble portion ; then reserve the rest for treatment with so- 

 dic carbonate, to determine soluble silica, and with hot 

 concentrated acid. 



Evaporate the solution to dryness with the addition of 

 a few drops of concentrated nitric acid towards the close 

 of the evaporation, to oxidize ferrous oxide and organic 

 matters, and eliminate silica (§ 58, or, 1). 



Dilute the filtrate from the silica to 1000 c.c, and 

 analyze it according to Scheme II., § 94, taking 400 c.c. 

 for a, 200 for b, and 400 for c. 



In b, a slight insoluble residue often remains, on dis- 

 solving the precipitate by sodic acetate in hydrochloric 

 acid ; in this case, dry the residue, ignite it and the filter, 

 digest the ash a long time with concentrated hydrochloric 

 acid, filter if necessary, and add the filtrate to the re- 

 mainder of the solution of the precipitate by sodic ace- 

 tate in hydrochloric acid, ignite and weigh the insoluble 

 residue, if there is any, and add it to the silicic acid. 



