972 



SCIENCE 



[N. S. Vol. XXXIII. No. 



erally, by the more intensive methods in vogue 

 in portions of the eastern states. Since profit- 

 able cropping becomes impossible in soils that 

 are strongly acid, the liming of soils is novc 

 receiving a good deal of attention. The sub- 

 ject of lime and liming is freely discussed in 

 the agricultural press, and the experiment 

 stations are asked to supply farmers with de- 

 tailed information as to the amounts and 

 kinds of lime needed for different soil types, 

 and for diiferent systems of cropping. In 

 view of the constantly increasing interest in 

 lime and its application, it is desirable that 

 reliable methods be provided for estimating 

 the lime requirements of soils. The search 

 for chemical methods that would supply the 

 desired information was begun many years 

 ago, and a considerable number of methods 

 have been proposed as suitable for this work; 

 unfortunately, however, agricultural chemists 

 find themselves unable to decide on any chem- 

 ical method that would give reliable results. 

 Some years ago a method was proposed by 

 Tacke that proved of certain value for the 

 moor soils of Germany. More recently Siich- 

 ting has attempted to improve the method by 

 correcting certain defects in it, but even in its 

 improved state the method leaves much to be 

 desired; it is cumbersome and far from re- 

 liable. Similarly, methods have been proposed 

 in the United States by Pettit and Hopkins 

 and, also, by Veitch. These methods have 

 been tested under different conditions, and 

 have failed to give concordant results. 



In view of the lack of a satisfactory method 

 for the quantitative estimation of soil acidity, 

 and in view of the evident need for a method 

 of this character, it is eminently proper to 

 make a careful study of new methods that 

 seem at all promising. Among the new meth- 

 ods that could be suggested, for this work, 

 the writer would include methods based on 

 certain bacteriological reactions. It is well 

 knovm that the development of bacteria in 

 any culture medium is directly affected by the 

 reaction of the latter. When the acidity of 

 the medium is increased beyond a certain 

 point, bacteriological development is retarded, 

 or entirely stopped. For this reason, it ap- 



pears evident that if to any neutral medium 

 there be added increasing quantities of acid 

 soil, a point will be finally reached when the 

 acid in the soil added would preclude further 

 development of the organisms. Following out 

 this line of thought, the writer prepared a 

 series of media of varying reaction. Several 

 portions of bouillon were prepared and ad- 

 justed to the following reactions : (a) ISTeutral, 

 (J}) one half per cent, acid, (c) one per cent. 

 acid, (d) one and a half per cent, acid, (e) two 

 per cent, acid, (/) three per cent. acid. 



When portions of these media were inocu- 

 lated with pure cultures of B. mycoides or B. 

 subtilis, growth occurred in the bouillon con- 

 taining up to two per cent, of acid; beyond 

 that the growth was very slight. When simi- 

 lar portions of bouillon had added to them 

 one half gram, one gram, three grams, five 

 grams and ten grams of soil, respectively, 

 growth occurred in the different tubes depend- 

 ing on the amount of acid present in the 

 medium, or that supplied by the soil. If, 

 previous to the addition of the soil, the latter 

 was mixed with ten per cent, of its own 

 weight of calcium carbonate, growth occurred 

 in all of the tubes, even those that had con- 

 tained bouillon with three per cent, of acid. 



These preliminary experiments demon- 

 strated, therefore, that the amount of acid 

 present in cultivated soils may be determined 

 quite accurately by comparing bouillon of 

 varying reactions vtdth equivalent quantities 

 of neutral bouillon containing varying 

 amounts of soil. The proposed method may 

 be utilized in still another direction, in that 

 varying quantities of soil be added to meas- 

 ured amounts of bouillon, and, after steriliza- 

 tion, the bouillon be inoculated with a stand- 

 ard culture of ammonifying bacteria. At the 

 expiration of a certain length of time the 

 ammonia formed could be distilled off and 

 determined in the usual way. Since the acid 

 added by the varying quantities of soil would 

 affect the development of the organisms to an 

 unequal extent, the amounts of ammonia 

 formed might be used as a fairly accurate 

 measure of the retarding effect of the acid 

 present in the soils. The quantitative rela- 



