solution employed was one consisting of 3 parts of crystallized sulphate of zinc and 8 parts of water, weighing 3 lbs. 2 oz. The electrodes were plates of platinum and zinc, each plate exposing an active surface of about 8 square inches. At the conclusion of each experiment, oxide of zinc was thrown into the solution to replace that removed by electrolysis, in order to prevent the zinc electrode from being acted upon by free acid.

Table IX.-Experiments on the Heat evolved by the Electrolysis of Sulphate of Zinc.

Pile of 7 cells.

Table X.-Experiments on the Heat evolved by the Standard Silver Coil. Pile of 5 cells..

The following tables give the results of the experiments for ascertaining the capacity for heat of the jar of solution.

Table XI.-Experiments on the Heat evolved by the Mercury Spiral in the jar of Solution of Sulphate of Zinc used in the experiments of Table IX. Pile of 5 cells.

Table XII.-Experiments on the Heat evolved by the Mercury Spiral in the can of water used in the experiments of Table X. Pile of 5 cells. 2 lbs. 11 oz. of water in the can.

From the last two tables we obtain for the capacity of the jar of solution used in the experiments of Table IX.,

3.0117 41.881

x 1283-7=1180.9.

From Tables IX. and X. we obtain for the quantity of heat

due to

A-C

A-B

× BC,

And for the actual quantity of heat evolved during electrolysis,

30.984

x 1180-9=1565°.

Hence 245707-1565-892° 7 the quantity of heat absorbed in the electrolysis of a quantity of sulphate of zinc corresponding to 0.5861 of a gramme of zinc.

The quantity of heat absorbed by the electrolysis of a quantity of sulphate of zinc corresponding to a gramme of zinc will therefore be 1523°.1.

The results of two other series of experiments, conducted in precisely the same manner as that I have just given, were 1547° and 1619° respectively. The mean of the three results is 1563°.

The heat absorbed by the transfer of the sulphuric acid from the oxide of zinc to the water was ascertained in the following manner. A solution of zinc similar to that employed in the experiments was acidulated with about 10 grammes of sulphuric acid. 7.9 grms. of oxide of zinc (prepared by igniting the carbonate) were thrown into this solution; and the heat evolved by its union with the free sulphuric acid was carefully ascertained, and properly corrected for the influence of the atmosphere. The capacity for heat of the jar of solution was then ascertained by the method of electrical currents. This being done, a fresh quantity of oxide of zinc was thrown into the solution, and the heat evolved again observed. The mean of the two experiments gave 378° for the quantity of heat evolved by the solution of 1.242 grm., the quantity of oxide of zinc corresponding to a gramme of zinc.

1563°-378=1185°, the quantity of heat absorbed in the decomposition of oxide of zinc into zinc and oxygen gas; and which ought therefore to be the quantity of heat evolved by the combustion of a gramme of zinc.

Combustion of Hydrogen Gas.

The apparatus employed in the experiments on hydrogen is shown in fig. 8. a represents a glass jar nearly full of a solution consisting of six parts of water and one of strong sulphuric acid, and containing platinum electrodes; b represents a glass tube for conveying the mixed gases to the pneumatic trough c. The glass stirrer d, being inserted in the small cork e, can, when not in use, be made perfectly tight by inserting the latter into the large cork which stops up the mouth of the jar. A coating of a viscid solution of rosin in turpentine was applied wherever it appeared necessary, in order to ensure perfect tightness. The quantity of mixed gases evolved was ascertained by the weight of water displaced in the bottle f; and hence the weight of liberated hydrogen was computed with the assistance of the best tables, regard being paid to the temperature of the gas, its hygrometric state, the barometric pressure, &c.

1

Table XIII.-Experiments on the Electrolysis of Dilute Sulphuric Acid, spec. grav. 1.103. Pile of 6 cells.

Table XIV.-Experiments on the Heat evolved by the Standard Silver Coil. Pile of 5 cells.

Table XV.-Experiments on the Heat evolved by the Mercury Spiral in the jar of Dilute Sulphuric Acid used in the experiments of Table XIII. Pile of 5 cells.

Table XVI.--Experiments on the Heat evolved by the Mercury Spiral in the can of water used in the experiments of Table XIV. Pile of 5 cells. 2 lbs. 11 oz. of water in the can.

From the above tables we obtain for the capacity for heat of the jar of dilute sulphuric acid used in the experiments of Table XIII.,

2.9987 41.402

X

2.9256 47.164

For the quantity of heat due to

42.642 3.2607

23.38 2.2181

x 1283-7=1155.

A-C

A-B

× BC,

-x 1283-7=3441°.8.

And for the actual quantity of heat evolved in the electrolysis,

40.381
23-38

x 1155-1994°.9.

Hence 3441°8-1994° 9-1446°-9, the quantity of heat absorbed during the electrolysis of a quantity of sulphate of water corresponding to 0.04243 of a gramme of hydrogen.

The quantity of heat absorbed by the electrolysis of a quantity of sulphate of water corresponding to a gramme of hydrogen will therefore be 34101°.

Two other series of experiments conducted in precisely the same manner, excepting that in the former of the two the capacity for heat of the jar of dilute acid was obtained by the method of mixtures, gave 34212° and 32358° respectively, as the heat absorbed per gramme of hydrogen liberated. The mean of the three results is 33557°.

A small portion of this quantity of heat absorbed is that due to the removal of water from the dilute acid; but the correction on this account is so exceedingly small as to be hardly worth