28 AGRICULTURAL RESEARCH AND THE FARMER : 



but never with soils that were known to be not sour. Nearly 300 

 tests were made, and in all cases the results were consistent. The 

 Department is now trying to improve the test in the hope of 

 arriving at a method of indicating not only the presence but the 

 amount of sourness. An attempt to discover a satisfactory test 

 is also being made by a member of the Advisory Staff attached to 

 the School of Agriculture, Cambridge. In this case the work 

 originated in the discovery that certain soils in the Cambridge 

 district which had been ignited, or burnt, did not thereby lose 

 their acid qualities. It has hitherto been supposed that the 

 various humic acids in the soil were driven off by ignition. 



As a method of checking such laboratory tests for acidity as 

 at present exist, and others which may from time to time be 

 elaborated, and also in order to study the whole question of 

 acidity in soils, an electrical apparatus has been set up at Rotham- 

 sted which is capable of measuring the acidit}' of a soil, not only 

 in amount but in intensity. For a sour soil contains a mixture 

 of acids of various strengths, and a statement of the total amount 

 of lime required to make the soil neutral gives no clue to the 

 " intensity " of the acid present. Two boxes of coins ma}' be of 

 exactly equal value, but if one contains all coppers, and the other 

 is partly made up of silver and gold coins, the weights of the boxes 

 are different. Similarly two soils may have exactl}' the same 

 " intensity " of acidity, and similar effects on the crop, but the 

 " quantity " of acidit^^ or the amount of lime required to correct 

 it, may differ considerably. So far, the only means of ascer- 

 taining the intensity of acidity in soils is by means of the electrical 

 apparatus referred to. It is based on a recognised method of 

 ascertaining the intensit}^ of acidity or alkalinity in liquids, but 

 various modifications have been necessarj^ to make it applicable 

 to the examination of soils. The apparatus is now working 

 satisfactorily, and it is hoped that the investigation wiU throw 

 much needed light on the subject of acidity in soils, and possibly 

 lead to the development of simpler methods of estimating their 

 hme requirements. 



