102 
DR. ANDREWS ON THE HEAT DISENGAGED 
We have, therefore, for the heat disengaged during the displacement of 
C. F. 
1 grm. mercury by zinc .... 333° or 600° 
1 equiv. mercury by zinc . . . 4166° or 7499°. 
Salts of Platinum with Zinc. 
Soda-Chloride of Platinum and Zinc . — Of the salts of platinum, the double chloride 
of sodium and platinum is best adapted for this investigation. The complete preci- 
pitation of platinum by zinc is more difficult, and requires a longer time than that of 
any of the metals hitherto examined. This renders the corrections larger and the 
tinal results less exact. To ascertain the composition of the salt employed, 0*692 
grm. carefully dried were precipitated by muriate of ammonia and the precipitate 
ignited ; 0*298 grm, metallic platinum were obtained. The solution employed in each 
experiment weighed lOOgrms., and contained 0*721 grm. of the dry salt. 
I. Air 15°*4. Increment found 2°*94, corrected 2°*64. 
II. Air 16°*2. Increment found 2°*93, corrected 2°*62. 
I. II. Mean. 
902° 896° 899° 
Hence we have for the heat disengaged during the precipitation of 
C. F. 
1 grm. platinum by zinc . . . 899° or 1618° 
1 equiv. platinum by zinc . . . 11085° or 19953°. 
It would have been very interesting to have extended this investigation to other 
cases of metallic substitution, so as to have been able to present in one complete 
view the quantities of heat developed in all such cases ; but the facility with which 
some metals are oxidized, and the difficulty of precipitating others in a short space 
of time from their solutions, prevented me from further extending the foregoing re- 
sults. For convenience, I have collected in the following table the numerical quan- 
tities already obtained : — 
Of precipitated metal. 
1 grm. 
1 eqmv. 
Salts of copper and zinc . . 
. . 868 
3435 
Salts of copper and iron . . 
. . 592 
2342 
Salts of copper and lead 
. . 268 
1061 
Salts of silver and zinc . . . 
. . 426 
5747 
Salts of silver and copper . . 
. . 161 
2176 
Salts of lead and zinc 
. . 182 
2357 
Salts of mercury and zinc . . 
. . 333 
4166 
Salts of platinum and zinc. . 
. . 899 
11085 
To prevent mistake, it may be right here to state that the numbers in the first 
column express the degrees centigrade through which one gramme of water would 
