98 
DR. ANDREWS ON THE HEAT DISENGAGED 
containing 0‘360 grm. oxide were taken. A large excess of lead (15 grms.) was re- 
quired for complete precipitation. The thermal value of the entire was 106'0grms. 
I. Air 2l°'5. Increment found 0°'89, corrected 0°’77- 
IL Air 21°‘5. Increment found 0°‘89, corrected 0°'77* 
I. II. Mean. 
284° 284° 284°. 
Formiate of Copper and Lead. — The solution was adjusted as before. 
I. Air 17°‘2. Increment found 0°'82, corrected 0°'72. 
II. Air 17°'1. Increment found 0°'83, corrected 0°71. 
III. Air 16°-0. Increment found 0°-80, corrected 0°70. 
I. II. III. Mean. 
265° 269° 259° 268°. 
Hence we have for the heat evolved.during the precipitation of 
C. F. 
I grm. copper by lead .... 268° or 482° 
1 equiv. copper by lead . . . . 1061° or 1909°. 
Salts of Silver with Zinc. 
The salts of silver are easily reduced by agitating their solutions with finely divided 
zinc. The sulphate and acetate were selected for experiment, and the results will be 
found to afford a further illustration of the general principle laid down in the com- 
mencement of this paper. The secondary development of heat was also clearly mani- 
fested, and continued for a considerable period of time, but gradually diminished in 
intensity. The two following observations will exhibit the amount of this heat, which, 
in the case of the salts of silver, must be chiefly ascribed to voltaic action. The 
annexed numbers give the increments of heat observed at intervals of two minutes, 
during each of which the agitation was continued in precisely the same manner. A 
few drops of the liquid having been removed after the first period of agitation, gave 
afterwards not the slightest opalescence with chloride of sodium, showing that the 
metallic precipitation was then finished 
Sulphate of silver. 
Acetate of silver. 
First increment . 
. . 1°96 
f94 
Second increment. 
. . 0-14 
0T2 
Third increment . 
. . 0-12 
0T2 
Fourth increment . 
. . 010 
0-08 
Fifth increment . 
. . 0-09 
0-06 
Sixth increment . 
. . 0-04 
0-06 
The final temperature of the liquid was about 0°7 above that of the surrounding 
air. The existence of a considerable amount of voltaic action was clearly shown by 
the evolution of hydrogen gas from the surface of the precipitated silver. 
Sulphate of Silver and Zinc. — The weight of the solution taken was 100 grms. An 
