October 8, 1915] 



SCIENCE 



507 



planations of the phenomena have never been 

 satisfactory. It is for the most part not an 

 absorption phenomenon but a true chemical re- 

 action consisting of an exchange of bases be- 

 tween a soluble salt and silicate, or else a neu- 

 tralization of acid substances by the base of a 

 salt giving rise to a soluble acid, as in the ease 

 in acid soils. In the case of peats and soils 

 high in organic matter, organic compounds 

 may cause similar phenomena. The writer 

 has been unable to obtain or find any data 

 which on careful consideration would lend 

 support to the colloid absorption theory of soil 

 acidity. 



The new test for soil acidity which the 

 writer had previously described" has now been 

 tried on a very large number of soils and 

 found entirely satisfactory. As is obvious, it 

 is absolutely necessary to use neutral calcium 

 chloride and zinc sulphide in the test. 

 Merck's reagents have given perfect satisfac- 

 tion. In reply to Harris,^ the writer wishes to 

 state that acid soils react without the use of 

 calcium chloride and hence his comment does 

 not apply. 



Although soils are composed for the most 

 part of silica and silicates, yet the function of 

 the silicates in soil fertility has been almost 

 entirely ignored. Their function in the in- 

 organic world is analogous to that of the pro- 

 teins and carbohydrates in the organic world. 

 The complex nature and behavior of the 

 silicates makes possible the great regulatory 

 processes going on in soils. The property of 

 certain silicates by means of which they 

 change from an active acidic state, a condi- 

 tion in which they actively take up bases from 

 solution, to a condition of inactivity, and also 

 the change in the reverse direction, is of the 

 greatest importance. This property makes 

 possible the presence of an enormous amount 

 of such silicates which prevent undue loss by 

 leaching without giving rise to the excessively 

 acid condition which would otherwise be 

 necessary. The root hairs of plants are prob- 

 ably among the most delicate of aU external 

 organs in either plant or animal life. In the 



5 Loc. cit. 

 B Loc. cit. 



soil there are a great variety of processes going 

 on, resulting undoubtedly in the formation of 

 not only beneficial substances, but also of some 

 harmful ones. If this is the case, it is prob- 

 able that nature has made some provision for 

 inhibiting the deleterious action of the harm- 

 ful substances on the delicate root hairs. It 

 seems possible that the silicates may form 

 temporary combinations with these substances 

 and thus prevent unfavorable action on the 

 root hairs. The wonderful influences, in other 

 than physical ways, of a small amount of such 

 silicates commonly called clay, on the fertility 

 of sandy soils has been known for a long time, 

 and a consideration of the above aids greatly 

 in its explanation. The writer has in prepara- 

 tion a detailed paper dealing with the subject 

 of soil acidity and related phenomena. 

 Depaetment op Soils, • ^BUOG 



Wisconsin Experiment Station, 

 University op Wisconsin 



a new method of measuring the concentra- 

 tion op the soil solution around the 

 soil particles 

 In conducting a thorough investigation on 

 the general subject of soil temperature the in- 

 fluence of soluble salts on the lowering of 

 freezing point of soils was also studied. It 

 was observed that the phenomena of super- 

 cooling and freezing behaved in moist soils 

 exactly the same way as in solutions. These 

 facts suggested the ideas that the freezing 

 point method might be employed to measure 

 the concentration of the soil solution around 

 the soil particles. In order to ascertain 

 whether or not this could possibly be done a 

 series of experiments was instituted, using 

 different classes of soil with various moisture 

 contents, or known concentration of solutions. 

 It has been found that the freezing point of the 

 soil solution around the soil particles can be 

 determined with great ease. Solidification can 

 be started when the soil mass is supercooled to 

 only about 0.2° C, by simply moving the 

 thermometer in the soil. The starting of the 

 solidification is far easier in soils than in 

 solutions. The freezing point of soils can 

 be determined even when the moisture eon- 



