§ 101. THE CHEMICAL ANALYSIS. 179 



off 4000 CO. again, and repeat this oj^eration for the third 

 and fourth time, or even more, as may be desired. 



Ulbricht found, that after the third or fourth extract, 

 the amount dissolved, at least by distilled water free from 

 carbonic acid, remained nearly constant, and that the 

 composition of one of these last extracts would furnish 

 the means for estimating the lasting fertility of the soil. 



It will usually answer to examine quantitatively the 

 first, third, fifth, and seventh extracts by carbonated 

 water. 



Interesting results may be obtained also by treating 

 the soil in the manner above directed with water contain- 

 ing 0.5 gmi. of ammonic chloride in the litre, in addition 

 to the usual charge of carbonic acid. 



Treatment of the Soil with Hot Concentrated 

 Hydrochloric Acid. 



101. If the soil contained a very large proportion of 

 calcic carbonate, the residue insoluble in cold acid may 

 be treated with hot acid ; otherwise the separation of the 

 insoluble from the soluble part by filtration is too difii- 

 xjult, and it is better to begin with a fresh portion of soil. 

 Pour 300 c.c. of concentrated acid over 150 grms. of the 

 air-dried soil, or over the whole of the residue insoluble 

 in cold acid in case carbonates were present in large 

 quantity, in a large flask, add a few drops of nitric acid 

 to oxidize slimy matters that might obstruct the filter, 

 heat to boiling with constant agitation, and continue to 

 boil gently for exactly an hour ; dilute the solution with 

 twice its volume of water, and, after letting the mixture 

 stand quietly for a short time, decant the liquid into a 

 filter that is double at the bottom ; treat the insoluble 

 residue in the flask at least three times with boiling wa- 

 ter, filter the liquid each time, and finally bring the resi- 

 due itself on the filter, and wash it thoroughly with boil- 

 ing Avater. 



Evaporate the solution and washings to dryness, with 



