1898 - 99 .] Dr Galt on Heat of Combination in Alloys. 621 
been found for alloy No. 5, but the larger heat of solution for the 
latter indicates that the excess in it of combined zinc (*23 gramme), 
over the quantity (’1375 gramme) chemically equivalent to the 
copper (’1325 gramme) present, apparently exerted a cooling effect. 
The difference between the two heats of solution is 0*22° C., or 0*44° 
C. per gramme of metal dissolved. The quantity of nitric acid used 
was 70 cubic centimetres of density D360 at 15° C. ; the water 
equivalent of the apparatus was 3 5 grammes. The result works 
out at 28 ‘07 gramme- water heat units centigrade per gramme of 
metal; but one gramme of the mixture contained ’54 gramme of 
alloy No. C, so that for one gramme of this alloy the value would 
be 28'07 x 1 ^ ) T ° = 52, which is near the value otherwise obtained as 
the heat of combination per gramme of this alloy. Thus again it 
is shown that for alloy No. 5 the heat of combination of the 
copper with its equivalent of zinc is exactly neutralised by the 
cooling effect produced by the excess of zinc present. 
