DURING METALLIC SUBSTITUTIONS. 
99 
equal portion of the same solution yielded, on analysis, 0*600 grm, chloride of silver, 
corresponding to 0*452 grm. metallic silver. The thermal equivalent of the solution of 
sulphate of zinc obtained after precipitation was 99*6 grms. water, and of the vessels, 
&c. 6*8 grms. 
I. Air 16°*6. Increment found 1°*96, corrected 1°*82. 
II. Air 15°*2. Increment found 1°*93, corrected l°*80. 
III. Air 15°‘2. Increment found 1°*92, corrected 1°*79. 
I. II. III. Mean. 
428° 424° 421° 424°. 
In another set of experiments a weaker solution was employed, which gave, on 
analysis, 0*571 grm. chloride of silver. The thermal value of the whole was now 
106*7 grms. 
I. Air 18°*2. Increment found 1°*80, corrected 1°*72. 
II. Ail' 18°‘0. Increment found 1°*80, corrected 1°*72. 
III. Air 18°*1. Increment found 1°*81, corrected 1°*73. 
I. II. III. Mean. 
427° 427° 429° 428°. 
Acetate of Silver and Zinc . — 100 grms. of the solution gave 0*600 grm. chloride of 
silver. 
I. Air 16°*4. Increment found 1°*94, corrected 1°*82. 
II. Air 15°'2. Increment found 1°*93, corrected 1°*81. 
III. Air 15°*0. Increment found 1°*93, corrected 1°*80. 
I. II. III. Mean. 
428° 426° 424° 426°. 
This result is identical with the mean number deduced from the experiments with 
the sulphate. We have, therefore, for the heat evolved during the precipitation of 
C. F. 
1 grm. silver by zinc .... 426° or 767° 
1 equiv. silver by zinc .... 5747° or 10345°. 
It has been already remarked that the nitrates do not in general yield the same 
thermal results as other salts, in consequence of the tendency of the nitric acid to 
decompose, which introduces other chemical actions in addition to the metallic pre- 
cipitation. Approximate results were, however, obtained with the nitrate of silver. 
100 grms. of a solution of nitrate of silver, containing 0*71 1 grm. of the dry salt, gave in 
three trials 2°*12, 2°*13 and 2°1 l,as increments, without any correction being applied. 
On continuing the agitation for periods of two minutes, and observing the temperature 
at the end of each period, the increments followed a singular law, being at first very 
small, and afterwards suddenly increasing. The march of the thermometer will be 
readily understood by inspecting the following numbers, which give the temperatures 
observed at the end of every two minutes of agitation. 
