OF THE ALLOYS OF COFFEE AND ZINC. 
535 
But the total heat evolved on the dissolution of chlorine gas in water will be 
greater than this by the thermal equivalent of the work done on it by the atmosphere, 
viz., 582 calories (at 18° C.). 
i.e., CL. Aq = 4977 (at 18° C.). 
Thomsen"^ gives CL. Aq = 2G00. 
On communicating with Professor Thomsen it appeared that the latter statement 
is incorrect, and he kindly gave the results of two unpublished experiments whose 
mean, 4870, is not very different from the author’s determination.] 
Series II.— Mixed Ammonium Chloride and Ferric Chloride Solutions 
AS Solvent. 
If finely divided copper is immersed in a mixture of NII_^.C1 and FeoClg solutions it 
is rapidly attacked with formation of cupric and ferrous chlorides. 
Similarly, zinc dissolves with production of zinc chloride and ferrous chloride. 
In neitlier case is there an evolution of gas, and the I'eactioii takes })lace 
quantitatively. 
This point was tested by dissolving weighed quantities of copper, zinc, mixtures, 
and alloys of the metals in separate portions of the solution, and then estimating the 
ferrous chloride produced. 
The presence of ammonium chloride appears necessary, in practice, for the rapid 
dissolution of the metals and their alloys. 
It may be that a thin film of cuprous chloride is first formed over the immersed 
metal, and that the conversion of this into the soluble cupric salt is hastened by the 
solvent action of the ammonium salt. 
A very strong solution of the chlorides was found essential to success, and that 
finally employed contained in each litre 182 grammes FeoClgand 107 grammes NHj^CL 
With tins solution the disappearance of the metallic powders seldom occupied 
more than two minutes, and very frequently not more that one and a-lialf minutes. 
Specific Heat ofi the Solution. 
A mercurial thermometer was constructed with a cylindrical bulb of some 15 cub. 
centims. capacity. Two marks on the stem corresponded to 25° C. and 95° C., and in 
order to reduce its length, a small reservoir had been lilown between the marks. 
The quantity of heat evolved by this thermometer during the fall of the inercury 
from mark to mark was determined by immersing its bulb in 500 grammes of water in 
* ‘ Tliennoehemische Uiitersuchungen,’ vol. 2, p. 400. 
