F. S. Mark 



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under reduced pressure 7 milligrams of carbon dioxide per 100 gm., an 

 amount which scarcely exceeds the unavoidable experimental error, and 

 certainly shows that water alone did not decompose any appreciable 

 amount of organic matter under these conditions. 20 grams of 

 the Transvaal soil were now taken and boiled for 20 minutes at 50° C. 

 with 2 c.c. strong hydrochloric acid and 100 c.c. water. 19 milligrams 

 of carbon dioxide per 100 grams soil were obtained and on continuing 

 the process 11 milligrams. The contents of the distilling flask were 

 now boiled for 20 minutes at atmospheric pressure and 158 milligrams 

 were now evolved. It will be observed that the strength of the acid is 

 an important factor in determining the amount of decomposition, as this 

 soil yielded 422 milligrams carbon dioxide when boiled with the stronger 

 acid used in the test for the decomposition of organic matter. The 

 Sprengcl water pump was used to reduce the pressure, and considerable 

 care must be exercised during the experiment, especially when allowing 

 air to pass through the apparatus on the completion of the decomposition 

 of the carbonate. 



The results obtained by this method with eight acid soils tested 

 never, with the exception of Ohio I and Transvaal III, rose above 

 9 milligrams carbon dioxide per 100 grams soil, while on boiling at 

 atmospheric pressure ten times as much was found, and that after 

 all carbonate must have been decomposed. 9 milligrams of carbon 

 dioxide corresponds to 0'02 °/o calcium carbonate, and whether a soil 

 contains this amount or no carbonate at all is a matter of no great 

 importance. 



The following table gives a comparison of the results obtained for 

 the carbon dioxide in Transvaal III and Ohio I b} the various methods 

 tried. 



An attempt was made to isolate from Transvaal III and Ohio I 

 a portion of the organic matter which, boiled at atmospheric pressure 

 with dilute hydrochloric acid, should give off a much larger percentage 

 of carbon dioxide than the soil itself. For this purpose part of the 



