a Re 
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CHEMICAL CHANGES IN CALCIUM ARSENATE. y 
the absorption of carbon dioxid, to a mixture of calcium carbonate 
and dicalcium arsenate. It appeared that any increase in water- 
soluble arsenic oxid in commercial calcium arsenate during storage, 
_ therefore, would probably be the result of absorption of carbon 
dioxid from the air. 
Accordingly, the authors decided to determine both carbon dioxid 
and water-soluble arsenic oxid in all of the samples and subdivisions 
at successive intervals. Soluble arsenic oxid was determined by the 
official method of the Association of Official Agricultural Chemists 
and carbon dioxid in a specially designed apparatus similar to that 
described by W. H. Chapin.” This method did not give extremely 
accurate results but it is very rapid and sufficiently accurate for this 
work. Duplicate determinations seldom differed by more than 0.10 
per cent. The fact that the results here vary more than this from 
the curves drawn may be explained on the basis of uneven distribu- 
tion of the material in the barrels and the method of sampling. The 
subsamples were always thoroughly mixed, but they were taken from 
the barrels by means of a trier, and, since carbon dioxid must work 
its way through from the outside of the package, it is reasonable to 
suppose that three or four trierfulls might not always remove a 
strictly representative sample. Taken as a whole, however, the 
results leave no doubt of the fact that carbon dioxid is absorbed 
under certain conditions. 
The results of these examinations are reported in Table 2 and are 
also shown graphically in Figures 1 to 46. The results on all the 
samples obtained from one manufacturer are presented before those 
of another are shown. Within each of these groups the order is as 
follows: Unsubdivided sample kept at Washington; unsubdivided 
sample kept at Tallulah; portion of subdivided sample kept at Tal- 
lulah in original container; subdivided samples at Tallulah repre- 
senting the different container tests. The last subdivisions are indi- 
cated by figures following the letter designation as follows: 1, sheet- 
iron drum; 2, unlined sugar barrel; 3, paper-lined sugar barrel; 4, 
heavy hardwood barrel; 5, unlined veneer drum; 6, paper-lined 
veneer drum. 
In every graph the arsenic oxid values are represented by a solid 
line and the carbon dioxid values by a broken line. The curves 
are drawn in what seemed to be the most probable positions without 
attempting to calculate them. In order to bring out more clearly 
the relationship between their variations, the ordinate scale of arsenic 
oxid (As,O,) values has been magnified to five times that of the car- 
bon dioxid (CO,) values. The horizontal spaces on all the plots 
indicate intervals of three months, the initial ordinate representing 
in each case December 1, 1919. 
7J. Ind. Eng. Chem., 10 (1918): 527. 
