H. B. Hutchinson and K. MacLennan 87 



The detailefl analysis of the f)otassium chloride solution after 

 digestion with the soil had taken place showed that an interchange of 

 bases had occurred and large quantities of alumina and iron had come 

 into solution in the form of acid salts — in fact, the characteristic reaction 

 of the soils is attributed to the presence of alumina^ and iron compounds 

 which are loosely absorbed by soil colloid bodies. 



Two other methods, in which salts of weaker acids are used, have 

 been described. According to Loew (29) 50 grms. of finely ground air-dry 

 soil are digested with 200 c.c. of neutral 1-0 per cent, solution of sodium 

 or potassium acetate at room temperature for 24 hours. The acetic 

 acid is more easily displaced than the stronger mineral acids and is 

 estimated by the titration of an aliquot portion of the filtrate. 



The bases employed by Loew are obviously not such as would come 

 into consideration for the correction of soil reaction in the field, and Jones 

 (30) has accordingly used the calcium salt ; 5-6 grms. of soil are ground in 

 a mortar with 0-5 grm. neutral calcium acetate and then sufficient water 

 is added to make a stiff paste. Grinding is continued and a further 

 30 c.c. of water added and mixed for 30 seconds ; the whole is then 

 transferred to a 200 c.c. measuring flask, the volume made up to about 

 160 c.c. and allowed to stand (with occasional shaking) for 15 minutes, 

 after which water is added to make up to 200 c.c. and filtered. The 

 first 10 or 15 c.c. of the filtrate are rejected and a further 100 c.c. taken 

 for titration with phenolphthaleiu. This reading ■: 2 .< 1-8 x 1000 gives 

 the amount of lime- in lbs. per acre of two million pounds of soil. The 

 method is extremely rapid, but in our own tests has given far from 

 satisfactory results. 



A further group of methods rests in the absorptive capacity of the 

 soil for various alkaline compounds. In that of Wheeler, Hartwell and 

 Sargent (31) the soil is digested at room temperature for 42 hours with 

 a known volume of approximately N/10 ammonia. A portion of the 

 clear supernatant liquid is withdrawn and hydrochloric acid added to 

 throw down the humic acid ; after filtration the excess of acid is 

 estimated by titration. A colorimetric method was also attempted by 

 these authors. These and similar methods involving the use oi alkahne 

 compounds are, however, open to the objection that whether the soil 



1 Tlie unproductiveness of certain American soils has been ascribed to the presence, 

 in the soil, of soluble aluminium salts (Abbott, Connor and Smalley, Purdue Univ. Agric. 

 Exp. Stat., Bull. 170. 1913). 



^ Chalk (CaCOj) is evidently intended, and not lime (CaO) as stated in the original 

 paper. 



