37 



XI. G. A. CowiE. " The Mechanism of the Decomposition 



of Cyanamide in the Soil." Journal of Agricultural 

 Science, 1920. Vol. X. pp. 163-176. 



This pajier is of interest as showing- the occurrence in the soil 

 e)t chang-es v.hicli apparently are not brought about by micro- 

 org-anisms, but by active chemical agents not yet clearly recognised. 



it is known (see p. 55) that cyanamide undergoes decom- 

 position in the soil before it can be utilised by the crop as a 

 fertiliser. It is now shown that the decomposition proceeds in 

 tliree stages: (1) cyanamide gives rise to urea; (2) urea gives 

 rise to ammonia ; (3) the ammonia is oxidised to nitrate. The 

 first stage, the formation of urea, seems to be brought about by a 

 chemical agent and not by micro-organisms, but the agent has not 

 yet been discovered. The change proceeds more rapidly in clay 

 than in sandy soils, and it does not take place at all in pure sand, 

 in peat, or in fen soils. There is some indication that the decom- 

 jjosition agent may be a zeolite or active silicate. A sample of 

 Thanet sand taken from a boring through the London Clay near 

 Chelmsford was i\>und, even after ignition, to be active in decom- 

 posing cyanamide into urea. This particular sand has been shown 

 to C(jntain a constituent resembling a zeolite in being reactive and 

 jjossessing the property of softening hard water by the substitution 

 of sodium salts and possibly potassium for those of calcium and 

 magnesium. In following up this clue it was found that the addi- 

 tion of a definite zeolite prehnite to ordinary inert sand produces a 

 mixture capable of converting cyanamide into urea. 



The decomposition of urea and the oxidation of ammonia are 

 then brought about by micro-organisms in the usual way. 



XII. \ . A. Bkcklkv. " The Formation of Humus." 



journal of Agricultural Science, 1921. Vol. XI. 

 pp. 69-77. 



.Setting out from an observation by Fenton it is shown that 

 sugars, on treatment with acids, give rise to hydroxymethylfur- 

 furaldehyde, which readily condenses to form a substance closely 

 resembling humus. The author found indications of hydroxy- 

 methylfurfuraldehyde in a dunged soil and in rotting straw in which 

 humus was being produced. He suggests, therefore, that the 

 formation of humus in the soil proceeds in two stages : — 



1. — Carboliydrates react with acids to produce hydroxymethyl- 

 furfural. 



2. — Hydroxymethylfurfural condenses to form humus. 

 In addition, in the laboratory, there is produced some furfural 

 and la^vulinic acid. 



No evidence of the formation of hydroxymethylfurfural during 

 the decomposition of cellulose by Spirocha^ta cytophaga could be 

 obtained. 



XIII. V. A. Becklev. *' The Preparation and Fractiona- 



tion of Humic Acid." Journal of Agricultural 

 Science, 1921. Vol. XI. pp. 66-68. 



The author finds that humus may be fractionated according to 

 tlie following scheme : — 



