Jan. 15,1917 
Calcium Compounds in Soils 
67 
EXAMINATION BY ANALYTICAL METHOD 
In attempting to distinguish between calcium compounds in these soils 
by analytical data, the following determinations were made: Total cal¬ 
cium; acid-soluble calcium by two methods, using different strengths of 
acid; carbonic acid; water-soluble calcium; and water-soluble sulphates. 
methods of analysis 
The sample, after the removal of gravel and organic d 4 bris by sieving 
if necessary, was ground in an agate mortar, passed through a 100-mesh 
sieve, and dried at 105° C. 
The total calcium was determined by fusion with sodium carbonate, 
acidifying, removing the silica in the usual way and precipitating the 
calcium as the oxalate after the removal of iron and alumina, the usual 
precaution of double precipitation being taken. 
The acid-soluble calcium was determined by two methods designated 
“A” and “B,” respectively. 
In method A 5 gm. of soil were digested with 50 c. c. of 4 per cent 
hydrochloric acid for 12 hours, filtered, washed free of acid, and the cal¬ 
cium determined in the solution in the usual way by precipitation as 
oxalate. 
In method B 10 gm. of soil placed on a dry filter paper in a funnel 
were leached with 2 per cent hydrochloric acid and washed free of acid. 
Where no effervescence was observed, two portions of 20 c. c. each of 
acid were used; where effervescence was observed, successive portions of 
20 c. c. of acid were used until the evolution of carbon dioxid was no 
longer observed, and the soil was then washed free of acid. The cal¬ 
cium was determined as in method A. 
Carbon dioxid was determined in a Knorr apparatus, being absorbed 
in a Geissler potash bulb and determined by the increase in weight. 
Water-soluble calcium oxid and sulphur trioxid were determined by pre¬ 
cipitation from a water extract obtained by shaking 25 gm. of soil with 
250 c. c. of water for 2 hours, allowing it to stand for 12 hours, and 
filtering. 
The analytical data obtained in this way are presented in Table III. 
In conformity with the usual practice of recording soil analyses, calcium 
is stated in all cases as CaO, sulphates as S 0 8 and carbonic acid as C 0 2 
rather than as the ions Ca, S 0 4 , and C 0 3 . 
