39 



5. Comparison of Indications Obtained by Different Methods. 



Coml>arisoii of Iiidicatiois Obtained By '/ruo^' and Litnins 

 Methods. There is a qreat similarity between the indications obtained 

 by the Tniog- and the htmus methods as carried out in the present study. 

 For the most part, the reactions are the same if. in the Truo.c: test, we 

 indicate any dej^ree of acidity simply "acid." The discrepancies are, 

 in the main, between samples which show only a slight acidity by the 

 Truog method, most of these l)eini4- neutral to litmus. 



It might be mentioned here that it so hai)i)ene(l that the tests with 

 litmus were made after the soils had been arranged in order of their 

 color (p. 58) so that soils from the different sets, fields, types and 

 drifts were promiscuously intermingled, and it was only after the 

 reaction had been determined and recx>rded and the data reassembled 

 tliat the first intimation of the relation of reaction to type and drift 

 was obtained. 



Comparison of Reaction By flic Truoi!^ Method and the Carbonate 

 Content. A relation between the degree of acidity shown by Truog's 

 test and the carbonate content, as shown by the percentage of carbon 

 dioxide (Tables 21 to 23). may be pointed out. \\'here the content of 

 carbon dioxide is above 0.11 per cent no acidity is shown. In the case 

 of surface soils there seems to be no doubt but that some organic 

 matter is decomposed during the course of the carbon dioxide determi- 

 nation with the evolution of carbon dioxide and the percentage thus 

 raised slightly. Hence, it appears safe to assume that the showing of 

 even a very slight acidity Iw the Truog test indicates that carbonates in 

 any form are either lacking or present in so small an amount as to be 

 of no consequence. 



Coniparison of Reaction By Litmus Method zvith the Carbonate 

 Content. Since the indications attained by the litmus method agree so 

 well with those obtained by the Truog test, the same general agreement 

 between the reaction shown by it and the carbonate content would be 

 expected, and this is found to be true. 



Comparison of Indications Furnished By the Litmus. Truoi:; and 

 .immonia Methods. The results obtained b}- the ammonia method 

 agree only in a very general way with those found by the Truog and 

 Htmus methods. Between the degree of acidity from field to field as 

 shown by the ammonia method, on one hand, and the Truog and litmus 

 methods on the other, there is no relation. Nor does it appear possible 

 to select any arbitrary number of units of color in the first corre- 

 sponding with any particular decree of acidity as established by the 

 second. 



