N. M. Comber 371 



known not to be sour. A red colour developed in a few minutes in the 

 solutions in contact with the sour soils and a yellow or brownish-yellow 

 colour in the others. Tliis brownish-yellow colour is apparently developed 

 in all cases, and the red colour arising from the sour soils is due to the 

 combination of the brownish-yellow and violet colours. 



During the last nine months the test has been applied to a large 

 number of soils and its indications agree with those of the thiocyanate 

 test. 



The colour developed by aqueous potassium salicylate is seldom so 

 deep as that developed by alcoholic thiocyanate, and the soil takes longer 

 to settle from the water than from the alcohol. 



A 5 per cent, solution of salicylate is one of convenient concentration, 

 but more concentrated solutions give a quicker indication. 



[Received August IWi, 1922.) 



Journ. of Agric. Sol xn 26 



