CHANGE IN WEIGHT DURING CHEMICAL REACTION. 
251 
(still in terms of the E,.P.) = 0'15, and the mean — difierence = 0’16. We therefore 
obtain a close approximation to the truth by taking as a final mean E„P. = 107‘0 
± 0'15. With a sensibility, S, of the balance = 45, we find that the variation ±0‘15 
in the R.P. = 15/450 = ±'003 mgr. As the total mass in either pan was approxi¬ 
mately equal to 127 gr., the variation +’003 is equivalent to 1 in 42’3 millions. 
(8) After mixing the Contents of X.—On the following day (October 4) two 
additional groups of 3 R.P. determinations were obtained ; their mean values at 1G° C. 
were respectively equal to 107’0 and 107'1 ; the accuracy of the value of the R.P. given 
above was thus confirmed. 
The contents of X were now rapidly mixed and the vessel replaced. Observing the 
usual precautions, the relative weights of X and Y were frequently determined during 
an ensuing period of 6 hours. The first comparison showed that the value of the R.P- 
had increased from 107 to 122'4 ; but when the weighings were brought to a conclusion 
for the day the value had fallen to 107'8 ; it was observed that the decline was fairly 
uniform throughout the 6-hour period. The comparisons were continued on October 5 
and 6 and very fully repeated on October 10. Briefly the results were as follows:— 
Table VI. 
Date. 
R.P. values at 1G° C. 
Number of 
determinations. 
Maximum. 
Minimum. 
Differences. 
Means. 
October 4, 1911 . . 
122-4 
107-8 
14-6 
115-8 
14 
)) b , 
110-7 
106-1 
4-6 
108-3 
14 
» 6 „ . . 
111-1 
95-6 
15-5 
104-9 
8 
„ 10 „ . . 
109-2 
107-2 
2-0 
108-2 
60 
The flnal result obtained from the series of determinations on October 10 shows 
that the R.P. value had increased from 107'0 before mixing the contents of X, to 108‘2 
after mixing ; the difierence 1 '2 is equivalent to an apparent increase in the weight of 
X of ’027 mgr. 
(9) After mixing the Contents of Y.—As the variations in the apparent weight of 
X and its contents showed immediately after mixing some degree of uniformity, it 
was decided so to conduct the weighings, after mixing the contents of Y, that it would 
be possible to determine in this case the actual rate with which the decrease in the 
apparent weight proceeded. Accordingly, the solutions in Y were quickly mixed, 
both X and Y were then wiped and replaced in the balance, and the usual preparations 
completed for weighing. The first weighing was made 20 minutes after the reacting 
bodies had been mixed ; other weighings followed at known intervals, which though at 
first brief, became more extended as the experiment progressed. In this way there 
2 K 2 
