156 Estimation of Calcium Carbonate in Soils 



desiccator over strong caustic soda and a good vacuum obtained by 

 means of a Fleuss pump. The whole was allowed to stand for several 

 hours in order to ensure the decomposition of the carbonate, after which 

 time the contents of the basin were washed into the distillingf flask of 

 the carbon dioxide apparatus with 50 c.c. of water, and boiled for twenty 

 minutes. The absorbing Reiset tower was then detached and the 

 carbon dioxide estimated. Tl)e distillation was then continued for a 

 second period of twenty minutes, and also for a third, with the following 

 result. The figures are given in milligrams of carbon dioxide per 

 100 grams of soil. 



The results indicate the continued decomposition of something in 

 the soil which yields carbon dioxide but which can hardly be calcium 

 or any other earthy carbonate. Even if any carbon dioxide remained 

 dissolved in the acid solution standing in the vacuum, it would have 

 been removed during the first boiling, so that the carbon dioxide obtained 

 in the second and third boilings must have been freshly formed by the 

 slow decomposition of the organic matter in the soil. 



An attempt was then made to minimise the decomposition of organic 

 matter by substituting ammonium chloride for the acid — 



CaCOs + 2NH, . CI = CaCL + (NH,),C03. 



Hartleb and Stutzer^ used ammonium chloride instead of hydrochloric 

 acid, and estimated carbonate as ammonia. This method is open to 

 criticism, and was found to be quite unreliable for acid soils, the free 

 acid of which combines with the ammonia produced and thus renders 

 the results too low. In the case of a New Zealand acid soil less ammonia 

 came over in the distillation of ammonium chloride with soil than in 

 the blank distillation of the ammonium chloride solution itself 



. There can, however, be no objection to a distillation with ammonium 

 chloride if the carbon dioxide arising from the dissociation of the 

 ammonium carbonate is estimated, and the carbonate calculated from 

 this figure: this was done by the writer. 10 — 20 grams of the fine 

 soil were put into the distilling flask along with 75 c.c. of boileil water. 



' /.cil. aii(jew. Clieiii. 1899, xii. 448. 



