OF THE ALLOYS OF COPPER AND ZINC. 
533 
The water equivalent of the calorimeter, stirrer, and thermometer was determined 
by the method of mixture, an apparatus similar to that used by Thomsen in 
measuring heat of neutralisation being employed. 
Warm water was placed in an upper protected vessel, and when its temperature 
had been found, a plug was removed from the bottom, thus permitting the water to 
flow directly into cold water of known temperature contained in the calorimeter. 
In three successive experiments the following values were obtained for the water 
equivalent :— 
15’92 grammes, 15‘6 grammes, 16'3 grammes. 
The mean value of 16 grammes was adopted. 
In most experiments a rise in temperature of about 1° C. was arranged, as this 
was a sufficiently large interval to be read accurately, and yet was not large enough 
to necessitate the introduction of a considerable correction for radiation during the 
one or two minutes occupied by the process of dissolution. 
All the determinations were made with the room, as nearly as possible, at 18° C., 
and the temperature of the calorimeter and its water-jacket was always carefully 
adjusted to that of the room before beginning an experiment. 
Series L—-Chlorine-ivater as Solvent. 
Although the use of this solvent was ultimately abandoned, the actual procedure 
in performing an experiment was exactly similar to that employed in Series It. and 
III., and it will therefore be described in this place. 
An aqueous solution of chlorine containing 5’3 grammes per litre was prepared ; its 
lieat capacity was found to be sensibly equal to that of the water it contained. It 
was first sought to ascertain the heat of dissolution of copper. 
The copper employed was prepared— 
(a.) By dissolution of pure copper in nitric acid. Ignition of the nitrate, and reduc¬ 
tion of the resulting oxide by hydrogen. 
(5.) By precipitation of copper from pure copper sulphate solution by means of 
redistilled zinc. 
The copper powder was heated in dilute sulphuric acid, washed repeatedly with 
water, and then with absolute alcohol. 
After drying, it was heated to redness in a current of hydrogen to reduce the 
small quantity of copjier oxide which had formed during the washing and drying- 
processes. 
Copper, thus reduced in hydrogen, retains ’6 volume of that gas, but the heat 
developed by the union with chlorine of the quantity of hydrogen contained in the 
small weight of copper used is negligible. 
