10 The Ther mo-chemistry of the Alloys of Copper and Zinc. 



The method consists in finding the difference between the heats of 

 dissolution, in suitable solvents, of an alloy and of an equal weight of a 

 mere mixture containing the metals in the same proportion. 



The first series of experiments was made with an aqueous solution 

 of chlorine as solvent. Its application was limited to those alloys 

 containing less than 40 per cent, of copper, as it was impossible to 

 obtain those richer in copper in a sufficiently fine state of division to 

 enable them to dissolve. 



The results, though not altogether satisfactory, showed that the heat 

 of dissolution of an alloy was sensibly less than that of the merely 

 mixed metals. 



Incidentally it was found that the equation Clo.Aq = 2600 (Thomsen's 

 ' Thermochemische Untersuchungen ') is erroneous and, on inquiry, 

 Professor Thomsen gave a corrected value, 4870. The author finds 

 Clo.Aq = 4970. 



The most suitable solvents of the alloys are — 



(a.) Mixture of ammonium chloride and ferric chloride solutions. 



(b.) Mixture of ammonium chloride and cupric chloride solutions. 



The chemical actions involved are simple reductions, and no gases 

 are evolved. 



Two series of experiments made on twenty-one alloys yielded very 

 concordant results. They show that heat is evolved in the formation 

 of every alloy of copper and zinc yet tested. 



A sharply defined maximum heat of formation is found in the alloy 

 containing 32 per cent, of copper, i.e., corresponding to the formula 

 CuZno. It amounts to 52 -5 calories per gramme of alloy or 10.143 

 calories per gramme-molecule. There is some evidence of a sub- 

 maximum in the alloy nearly corresponding to CuZn. 



From these points there is a steady decrease in the heat of formation, 

 both in the case of alloys containing less than 32 per cent, of copper 

 as the amount of copper decreases, and also in the case of those con- 

 taining more than 50 per cent, of copper as the quantity of copper 

 increases. 



The results, in general, confirm the existence of intermetallic com- 

 pounds, and the values obtained are in accordance with those demanded 

 by Lord Kelvin's calculation of the molecular dimensions of copper 

 and zinc. 



