4 



Mr. A. D. Hall and Dr. N. H. J. Miller. [Mar. 30, 



chalk is visible only in the upper soil, and is there present in small rounded 

 nodules varying in diameter from 3 or 4 mm. downwards. 



I. — Calcium Carbonate in Rothamsted Soils. 

 A. Analytical. 



The first section of this paper deals with the determinations of the amounts 

 of calcium carbonate present in the soils and subsoils of certain of the plots 

 in the Broadbalk, Hoos, Agdell, and Little Hoos Fields, the samples having 

 been drawn at the dates specified above and again in 1904 — 5. As the 

 calcium carbonate is of artificial origin, and was probably distributed with 

 considerable irregularity, however much this may have been equalised by 

 the subsequent working to which the soil has been subjected, it cannot be 

 expected that the samples analysed will represent the whole soil of the plots 

 with the same degree of accuracy as would be attained in the case of some 

 original constituent of the soil. 



O 



Arable soils only are considered ; with soils in permanent grass the question 

 is complicated by the well-known action of earthworms, which, as demon- 

 strated by Darwin, bury the surface layer by constantly bringing fine subsoil 

 to the top. 



The determinations of calcium carbonate have been made by means of an 

 apparatus described by one of us in conjunction with Dr. E. J. Eussell.* 

 The results are calculated from the volume of carbon dioxide evolved on 

 treating the fine soil with dilute sulphuric acid in vacuo, due provision being 

 made to bring into account the carbon dioxide remaining dissolved in the 

 reacting liquid. In a few cases, where the percentage of calcium carbonate, 

 was very low, the carbon dioxide evolved by treating a considerable quantity 

 of the soil with acid was absorbed by caustic soda and determined by double 

 titration. For these determinations we have to thank Mr. Arthur Amos, 

 BA. The amount of magnesium carbonate present is too small to affect the 

 results, and in any case, as the real quantity sought is the amount of readily 

 available base in the soil, it is desirable to express it always in the same terms. 



The soil samples were all taken in the same way : a steel frame 6 inches or 

 1 foot square and 9 inches deep is driven into the ground, and its contents are 

 carefully picked out; this gives the soil proper. The surrounding soil is. 

 then dug away and the frame is driven down another 9 inches. The contents 

 now represent the subsoil at the second depth of 10 to 18 inches. The process 

 is then repeated to as many holes as may be required. In this way samples 

 are taken from four, six, or eight holes on each plot, according to its size. 



* Hall and Russell, ' Trans. Chein. Soc.,' vol. 81, 1902, p. 145. 



