H. B. Hutchinson and K. MacLennan 77 



Some observations on this question were made by Way (6), who employed 

 lime water, and further work might naturally proceed along these Unes, 

 or by adding solid calcium oxide in varying quantities to the moist soil 

 to be tested. The latter method promised, however, to approach more 

 closely to the conditions obtaining in our other bacteriological and 

 chemical experiments with soil in bottles, and was accordingly adopted. 

 We confined ourselves in the first instance to the study of some five 

 soils — Eothamsted, Millbrook, Woburn. Chelsea and Craibstone- -which 

 had been studied in other directions. 



The Method. The method originally adopted and to which we have 

 adhered throughout is based on the determination of the minimum 

 amount of hme required to render the soil water distinctly alkaline and 

 is as follows: 100 grm. lots of the air-dry soil to be tested are placed 

 in bottles of about 250 c.c. capacity ; accordiug to the character of the 

 soil (whether poor or rich, light or heavy) a number of dressings of 

 calcium oxide are then made, rising by increments of 0-1 grm. to 1-0 

 per ceut., or increments of 0-2 grm. to 2-0 per cent, of the weight of 

 soil. Sufficient water (50 c.c.) is added to moisten the soil, the bottles 

 are then tightly corked and shaken for a few seconds at intervals for a 

 definite period. This period is generally 24 hours, but actual com- 

 parisons have shown that the amount of change between 4 and 24 hours 

 is only shght. At the end of this time the contents of the bottles are 

 then transferred to, and washed in, a Buchner funnel with a further 

 200 c.c. of water ; the whole of the filtrate is then titrated with N/10 

 acid, using phenolphthalein as indicator. 



Within the range of applications made in the above manner it will 

 generally be found that a point is reached where the reaction of the 

 filtrate is distinctly alkaline, and the results of other investigations have 

 shown that where the alkalinity is such that 5-10 c.c. of N/10 acid are 

 required to neutralise the whole of the filtrate, this may be taken as 

 the limit to which calcium oxide must be apphed to the soil in order 

 to produce the best results. 



With heavier applications the concentration of the filtrate tends to 

 approach saturation point, but any increase in the application beyond 

 the amount necessary to bring the filtrate to the above-mentioned point 

 appears uudesirable; such apphcations tend to constitute "over- 

 liming" if made under ordinary conditions. The results of a few such 

 tests are given in Table I, and are plotted, together with data obtained 

 wth other soils, in Curve 1. 



The great difference in absorptive capacity of the various soils is 



