CHANGE IN WEIGHT DURING CHEMICAL REACTION. 
257 
Table VIII. 
At the time of sealing the bulb the barometric reading = 744 mm. 
Date. 
Pressure 
within bulb. 
Change in 
pressure. 
Change in 
volume of bulb. 
Equivalent 
change in 
Aveight. 
1 
November 16, 1911 . . 
744 mm. 
±0 
±0 
±0 
r „ 17 „ . . 
744 „ 
+ 0 
+ 0 
±0 1 
,, 18 ,, . . 
670 „ 
- 74 mm. 
- -0015 c.c. 
+ • 002 mgr. 
,, 19 ,, . . 
Not read. 
20 
611 mm. 
-133 „ 
- -0026 „ 
+ -003 „ 
After 
21 
578 „ 
-166 „ 
- -0033 „ 
+ •004 „ 
heating 
^>2 
587 „ 
-157 „ 
-•0031 „ 
+ •004 „ 
23 
587 „ 
-157 „ 
-•0031 „ 
+ •004 „ 
„ 24 „ . . 
593 „ 
-151 „ 
-•0030 „ 
+ ■004 „ 
,, 25 „ . . 
598 „ 
-146 „ 
-•0029 „ 
+ -004 „ 
L n 26 „ . . 
Not read. 
After 
r „ 27 „ . . 
1594 mm. 
+ 850 „ 
+ •0167 „ 
-•020 „ 
exposure < 
„ 28 „ . . 
1594 „ 
+ 850 „ 
+ •0167 „ 
-•020 „ 
to light 
1 „ 29 „ . . 
1674 „ 
+ 930 ,, 
+ •0183 „ 
-•022 „ 
relative weights of the two vessels, X and Y, are therefore to be attributed to the sum 
of the two variables, one of which tends to increase, and the other to decrease the 
weight of either vessel. If the two variables have been, and still are, equally 
operative in both vessels, there will follow strictly equal opposition effects ; as the 
sum of these = 0, the balance remains unaffected, and the presence of the variables 
remains unsuspected. In all probability this is just what happened in Landolt’s 
experiments with silver nitrate and ferrous sulphate. There is, however, one other 
possibility. Further experiments have proved that for the secondary reactions occurring, 
the period of induction may be very considerable ; that is to say, the primary reaction 
may proceed to a point where a first chemical equilibrium may be established, and 
then no further appreciable changes follow before the whole experiment is completed. 
Viewed mathematically, we have but re-stated the case ; in so far as the actual 
weighing is concerned, the results are precisely the same. 
The mixture left in the flask after concluding the experiments with the tantalum 
lamp, proved on examination to be very acid. The clear liquid obtained on filtering, 
contained in addition to acids, ferrous, ferric, and silver salts; the undissolved portion 
which was somewhat yellow, contained metallic silver, silver nitrate and some salts of 
iron. We must now leave the chemical problem here presented to be mor^ fully 
dealt with in some future communication ; but from the remarks made, it will be 
abundantly evident that the chemical equation set forth on p. 230 gives but a very 
incomplete representation of the actual facts ; that equation may indeed represent 
VOL. ccxii.—A. 2 L 
