160 Estimation of Calcium Carbonate in Soils 



humus was extracted with 4 "/„ ammonia after preliminary treatment 

 with 1 "/u hydrochloric acid, which was removed before extracting with 

 ammonia. Curiously enough, the percentage of carbon dioxide evolved 

 from the humus, which was dried in a desiccator over sulphuric acid, 

 did not increase, although the same experimental conditions were 

 maintained as before. 



Amos' observations on the occlusion of carbon dioxide in soil were 

 repeated and confirmed. It was found that occlusion of carbon dioxide 

 in air-dried soil does not take place to any appreciable extent. 



I have to thank Dr N. H. J. Miller of this laboratory for his 

 continued advice and assistance during the progress of this work. 



Summary and Conclusions. 



Boiling acid at atmospheric pressure decomposes organic matter 

 in soil with evolution of carbon dioxide, and thus renders the results 

 obtained for carbonate too high. Where there is a fairly large percentage 

 of carbonate, the error introduced in this way is of no great importance, 

 but in soils containing less than 1 "/o ^f calcium carbonate and especially 

 in acid soils, the error introduced by thus boiling with acid may be very 

 considerable. 



The weaker the acid used the better so long as there is fair excess. 

 The writer recommends for acid soils and those containing low percentages 

 of carbonate (as can be seen by making a rough preliminary test), 2 c.c. 

 of strong hydrochloric acid and about 100 c.c. of water: 20 grams of soil 

 should be used when the amount of carbonate is small. The acid may 

 be conveniently added by making up a solution containing 100 c.c. of 

 strong hydrochloric acid per litre, and introducing 20 c.c, of this solution 

 along with 80 c.c. of water. For most soils, 5 c.c. of strong hydrochloric 

 acid to 100 c.c. of water will be found convenient. 



If possible distillation under reduced pressure sljould be used, as 

 under this condition practically no decomposition of organic matter 

 takes place, while carbonate is readily decomposed: the distillation 

 should be continued for twenty minutes at a temperature of about 

 50° C. 



Since the above paper was ready for publication wo have learnt of the death of 

 the author at Breslau on May 13th. After working for a year in the Eothamsted 

 Laboratory Mr Marr proceeded to Breslau to work under Dr Th. Pfeiffer, and there 

 the course of a promising worker, who endeared himself to all with whom he came 

 in contact, was untimely cut short. A. D. H. 



