No. 1.] HARDENING REAGENTS. ee 
meet this decrease following the attainment of the maximum, 
later on. 
At the high temperature of 38° C. the increase in weight is 
not so great, and the subsequent decrease much greater than at 
the lower temperatures. Transferring the specimen after 
36 days at 38° C. to 10° C. does not affect the weight (vzde 
Specimen 1). 
The reverse change (vzde Specimen §) causes a rapid and 
large loss in weight. At the same time there was a corre- 
sponding decrease in volume. The effect of high temperatures 
will need further special study, but the temperatures between 
17° C. and 10° C. are without decided influence on the gain 
in weight. 
Percentage of Salts. —It appears that within the limits 
employed, the greater the percentage of bichromate of potash 
the less the increase in weight. In support of this statement 
the following figures are given :— 
AVERAGE INCREASE 
IN WEIGHT. 
4 Hemiencephala after 20 days in 4% Bichromate Solution = 59% 
4 “ “ ‘“ “6 zai “ “ = 36% 
2 “ ““ “e “ AT, “és “ = 24% 
2 ‘“ “6 “ ‘“ 8% ‘“é ‘“ —_— 15% 
There is, however, a difference in the reactions of specimens 
which these figures do not bring out, namely, that the smaller 
the percentage of bichromate of potash the more rapidly is the 
maximum weight attained. While the specimens in 8% bichro- 
mate of potash at the end of 640 days had increased from the 
figures above given (15%) to 21%, the specimen in 4% solution 
showed an increase to 30% at the end of the same time. 
The relative differences in weight are slightly less at the end 
of this longer period, but the general character and significance 
of the table is not thereby affected. 
Cause of Increase in Wetght. — The increase in weight, under 
the action of the bichromate of potash is due to the absorption 
of both water and the salt by the specimen. This is shown 
by putting the specimen in a weighed quantity of fluid and 
determining that the increase in the weight of the specimen is 
equal to the decrease in the weight of the fluid. 
