1916.] The Third Indian Science Congress. cix 



therefore to find that the attention of the agricultural investigator in 

 India tends to be concentrated on questions relating to the supply of 

 water to crops. At the same time, the other factors on which yield 

 depends are apt to be obscured and crop-production comes to be regarded 

 almost entirely as a question of water-supply. After ten years' observa- 

 tion of the crops grown on the Indo-Gangetic alluvium, during which a 

 good deal of first-hand experience in agriculture has been obtained— at 

 ±*usa in Bihar, at Lyallpur in the Punjab and at Quetta in Baluchistan— 

 the conclusion has been reached that a full supply of air in the soil is 

 quite as important as a sufficiency of water. While air is a necessary raw 

 material for the soil organisms and for the roots of plants wherever they 

 may be grown, efficient soil ventilation is found in practice to be particu- 

 larly difficult on alluvial soils like those met with over large areas of the 

 plains of India. Alluvial soils, like those of the valleys of the Ganges 

 and Indus, pack very readily and always run together on the surface 

 after heavy ram, forming a well-defined crust well known to any cultiva- 

 tor as the papri. Two chief factors are responsible for the ease with 

 which these alluvial soils form surface crusts after light showers and lose 

 their porosity altogether after a long continued rain. In the first place, 

 the soil particles are small in size and exhibit no very great range in 

 diameter and, in the second place, much of the rain comes in heavy 



continuous torrents quite unlike anything experienced in temperate 

 regions. 



Several examples of soil ventilation were discussed in detail. The 

 yellowing of peach trees at Quetta, which at present sight appeared to be 

 a disease, turned out on investigation to be due to defective soil aeration 

 and could be reproduced at will either by deep planting or by over- 

 lrrigation. The factors on which success in green- manuring depends were 

 then considered. Copious aeration has been found to be necessary in this 

 operation, otherwise air becomes a limiting factor in the growth of the 

 succeeding crop. It was also suggested that in maturation and in the 

 development of quality, copious soil aeration is much more important 

 than has hitherto been suspected. 



Section of Chemistry. 

 (Chairman — Prof. J. J. Sudborough, D.Sc, Ph.D.) 



Some Additive Compounds of Trinitro-Benzene. — By J. J 



Sudborough. 



Note on the Estimation of Iodine values by the Broniate- 

 Bromide Method. — By J. V. Lakhumalani and J. J. 

 Sudborough. 



The authors have made a critical examination of Winkler's method 

 of determining the Iodine values of fats and oils by an acidified bromate- 

 bromide mixture (compare Weiser and Donath, Zeit. Untersttch. Nahr. 

 Genuss., 1914, XXVIII, 65). 



The method gives excellent results with most fats and oils provided 

 the reacting mixture is not exposed to light. In the presence of light the 

 values come too high, probably owing to bromine being used up by a pro- 

 cess of substitution. 



Weiser and Donath claim that acids with olefine linkings also giv« 

 »od results by the method. According to the authors the esters — 

 methyl or ethyl — of unsaturated acids give extremely low iodine values 

 % the Bromate method under the usual conditions. 



