248 REPORT—1899. 
straight line one might expect all the results for mixtures to lie on this line ; 
and this is approximately true for all, except in the case of those mixtures 
containing from about 15 to about 40 per cent. copper which indicate a 
drop, probably due to unavoidable errors in the experimental work. 
The difference between the absolute heat of solution of 1 gramme of 
each mixture and its corresponding alloy indicates the heat of com- 
bination of the metals in forming 1 gramme of alloy. These differences 
are shown on fig. 2, and they indicate that the heat of combination is 
at first negative, which reaches a maximum when the alloy contains about 
16 per cent. of copper. With greater percentages of copper the negative 
value of the heat of combination rapidly falls to zero and then becomes 
positive. The maximum positive value is very soon reached at about. 
38 per cent. copper, which is near the formula Cu,Zn;. Beyond this 
point the heat of combination gradually kecomes less, until at 90 per cent. 
copper it almost vanishes. 
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