ESTIMATION OF CALCIUM CARBONATE IN SOILS. 



By F. S. mark, M.A., B.Sc. 

 Carnegie Research Scholar. 



Rothamsted Experivient Station. 



This work was undertaken at the suggestion of Mr A. D. Hall, 

 whose attention was drawn to the subject by some abnormal results 

 obtained in the estimation of calcium carbonate in certain soils from 

 different parts of the world characterised by their high humus content 

 and their acid reaction to litmus paper. Boiled with diluted sul- 

 phuric acid (1 : 1 H2SO4), most of these soils yielded an amount of 

 carbon dioxide (estimated by Brown and Escombe's double titration 

 method) equivalent to a percentage of 1 — 3 of calcium carbonate in 

 the air dried soil: while others yielded still higher amounts. It is 

 quite possible that a soil may be acid in reaction and yet contain 

 carbonate \ but such percentages are quite incompatible with the strong 

 acidity present in these cases. It seemed possible that the carbon 

 dioxide evolved from such soils when boiled with acid resulted from the 

 decomposition of unstable organic matter: and this is the conclusion 

 arrived at by the writer. 



The apparatus used in the investigation was that described by 

 Amos-. 



Two soils which showed specially high percentages of carbonate 

 (as calculated from the carbon dioxide evolved) were selected as test 

 soils. These will be referred to under their Laboratory numbers, Ohio I, 

 and Transvaal III: in addition use was made of many other soils both 

 acid and normal. They were used in an air dried condition, and powdered 

 till they would pass through a sieve with square holes, passing particles 

 less than 04 mm. in diameter. The test for decomposition of organic 

 matter with production of carbon dioxide was carried out as follows. 

 10 grams of soil were placed in a basin with 50 c.c. of boiled water, and 

 15 c.c. of strong hydrochloric acid added. The basin was placed in a 



1 Hall, Miller, and GimingLam, Proc. Boy. Soc. B. 1908, 80, 196. 

 * Journal of Agricultural Science, 1905, i. 322. 



