ON THE HEAT OF COMBINATION. 73 
Nitrate of Barytes and Sulphate of Soda. 
° 
Temperature of air...... ny One ve 144 
Increment observed............+. 0°75 
Heat for | grm. BaO, SO,........ 20°5 
Heat for 1 equiv. BaO, SO; ...... 2989 
Nitrate of Barytes and Sulphate of Zine. 
Temperature of air.......... 139 14-1 
Increments observed ........ 0°83 0°83 
Heat for 1 grm. BaO, SO,.... 22°0 22:0 
Heat for 1 equiv. BaO, SO; .. 320°7 
Nitrate of Barytes and Sulphate of Copper. 
Temperature of air.......... 144 14-4 
Increments observed ........ 0°88 0°91 
Heat for 1 grm. BaO, SO, .... 23:0 245 
Heat for 1 equiv. BaO, SO, .. 346°2 
The salts of lead were next examined. The precipitation of the sulphate 
of lead took place with the same facility as that of the sulphate of barytes, 
the thermometer attaining the maximum in eight minutes. 
Acetate of Lead and Sulphate of Magnesia.—The acetate of lead was pure 
and in crystals, 4°1'7 grms. precipitated by oxalate of ammonia gave 2°4.54 grms. 
oxide of lead, which exactly agrees with the theoretical composition of the 
salt. In each of the following experiments, 30°80 grms. acetate of lead were 
taken, corresponding to 24°63 sulphate of lead :— 
Temperature of air.......... 12°7 123 
Increments observed ...... soy LO 0°97 
Heat for 1 grm. PbO, SO,.... 9:9 5%) 
Heat for 1 equiv. PbO, SO, .. 187°6 
Acetate of Lead and Sulphate of Soda. 
Temperature of air .......... 123 12-9 
Increments observed ........ 0°84 0°86 
Heat for 1 grm. PbO, SO,.... 8:3 85 
Heat for 1 equiv. PbO, SO, .. 159°2 
Acetate of Lead and Sulphate of Zinc. 
Temperature of air.......... 123 139 
Increments observed ...... oe = O41 0°37 
Heat for 1 grm. PbO, SO,.... 4:1 3°7 
Heat for 1 equiv. PbO, SO, .. 739 
_ In the last experiment the precipitation was so slow that the thermometer 
did not attain the highest point for thirteen minutes after the solutions were 
mixed. 
When the salts of lead are precipitated by a neutral oxalate, the heat dis- 
engaged is much greater than when they are precipitated by a sulphate. I 
have not examined in detail the increments of temperature in this class of 
precipitations, but in one experiment, in which the acetate of lead was pre- 
cipitated by the oxalate of potash, 36°2 units of heat were obtained for each 
gramme of oxalate of lead. 
| In the experiments next to be described, a dilute acid was substituted for 
one of the neutral solutions. 

