528 TRANSACTIONS OF SECTION B. 



reacting substances in the clays must be of a kindred nature — zeolitic double 

 silicates. 



The absorption of ammonium salts by soils must be due chiefly to such double 

 silicates, for the character of the reaction is but little affected by the presence of 

 calcium carbonate. 



It is found that when the clay is in excess the reaction between it and 

 ammonium chloride can be expressed by the equation — 



Ka(Ammonium absorbed b y clay)' 

 Final concentration of solution in ammonium 



"When the solution is in e.Kcess the amount of ammonium absorbed is propor- 

 tional to the strength of the solution. Cur^-es have been constructed showing the 

 variation of the absorption with the strength of the solution for various ammonium 

 salts, potassium and barium chlorides, and hydrochloric acid. 



2. Oxidation in Soils and its Relation to Productiveness. By Francis V. 

 Dakcishire, B.A., Ph.D., and Edward J. Russell, D.Sc. 



All soils possess the power of absorbing oxygen — some to a marked extent. 

 The authors have devised an apparatus for measuriug the rate of absorption, and 

 have studied the influence of various factors, and also the connection with the 

 productiveness of the soil. 



It has been found that oxidation is mainly, but not entirely, due to the activity 

 of micro-organisms; oxidation still goes on in soil sterilised at 120° C, or by 

 treatment with 1 per cent, mercuric chloride ; but the rate is only about one-fifth 

 of what it was. 



The rate of oxidation does not entirely depend on the amount of organic 

 matter present in the soil. Moisture is essential ; as its amount increases the 

 rate of oxidation also increases until near the point at which the soil becomes 

 waterlogged. The addition of calcium carbonate, or of sugar, increases the rate: 

 in the latter case the maximum increase occurs with 1 per cent, of sugar. Small 

 quantities of poisons like mercuric chloride, thymol, copper sulphate, &c., also 

 increase the rate till the optimum amount, '01 per cent., is reached. Further 

 quantities reduce the rate considerably. 



Somewhat different results were obtained with partially sterilised soils. If a 

 soil is exposed to vapours of chloroform, carbon disulphide, or toluene, and the 

 antiseptic then removed in a current of air, the rate of oxidation markedly increases. 

 A similar result is obtained when the soil has been exposed to sunlight or to a 

 temperature of 85° 0., insufficient to kill sporoi^. 



The rate of oxidation is closely parallel to the productiveness of the soil. For 

 a series of similar soils of which the cropping power is known it is found that the 

 most productive has the highest rate of oxidation, and that the others follow in 

 the same order for both properties. The parallelism holds, not only lor soils in the 

 natural state, but also, with certain limitations, for soils which hare been arti- 

 ficially treated. Thus partial sterilisation by heating to 95° increases the rate of 

 oxidation, and also increases the productireuess ; treatment with volatile anti- 

 septics has the same result. It is essential, however, that the soil conditions 

 should be aerobic, as in arable soils ; pasture soils, where the conditions are les."* 

 perfectly aerobic, do not follow the general rule. In view of this difference the 

 authors suggest that the rate of oxidation aSbrds a measure of the bacterial activity, 

 which is closely connected with productiveness. 



3. A Method of Determining Indigotin. By W. Popplewell Bloxam. 



The author was employed in India during the years 1902-1904 in research 

 work on plant indigo, and during the year 1905 publication was made of the 

 results obtained—' An Account of the llesearch Work in Indigo, carried out at 



