68 Royal Irish Academy. 



May 24. — Mr. Robert Mallet read a paper " On the Physical Pro- 

 perties and Electro- Chemical and other Relations of the Alloys of 

 Copper with Tin and Zinc." 



These experiments are collateral to the researches on the action 

 of air and water on iron, upon which the author has been engaged 

 at the desire of the British Association. In the progress of these 

 inquiries, it became necessary to determine the action of solvents on 

 iron in presence of various definite alloys of copper and tin and of 

 copper and zinc. Hence it was requisite to form many such alloys 

 in rigidly assigned proportions as to their constituents, a matter 

 known to experimenters to be one of difficulty, especially in the case 

 of so oxidable and volatile a metal as zinc. The difficulties were 

 overcome by a peculiar arrangement of apparatus, permitting the 

 metals to be fused and combined in close vessels. The results were 

 verified by assay. Having these alloys which belong to the classes 

 of brass or gun-metal, of which most of our instruments of precision 

 are made, and their constitution being atomic and certain, it seemed 

 useful to determine some of their properties for practical purposes. 

 The results are given in the two tables prefixed, pp. 66, 67. 



The author has also determined the numerical conditions govern- 

 ing the rate of solution, or amount of loss sustained in a given time 

 by equal surfaces of iron in solvent menstrua, when in presence of 

 all these alloys, and of the alloys themselves. Tables of these were 

 presented : the results do not seem to coincide with the law of volta 

 equivalents, which is explained by showing galvanometrically that 

 the s — and e -f- metals of the alloy are often not acted on equally 

 by a solvent; thus, that an alloy of Zn y + Cu^ may assume a cop- 

 per surface after a certain time of reaction. This circumstance, the 

 author has shown, suggests a method of determining the molecular 

 arrangement of an alloy ; and, in general, whether any alloy be a 

 chemical compound or a mixture. 



The author also enters into several details as to peculiar, and, in 

 some cases, singular reaction of these and other alloys upon solutions 

 of the salts of their own metals : thus, certain alloys of lead and 

 zinc decompose solutions of lead as rapidly as pure zinc ; while 

 others, containing much zinc, act as lead towards the salts of lead. 



In the case of three metals, A, B, C, whereof A is s + , and C is 

 s — to B, the author investigates the question as to what will be 

 the electro-chemical relation of the atomic alloys of A^ + Cy to- 

 wards B, in solvent menstrua ; and in the class of alloys of copper 

 and zinc, has determined the alloy of no action, with reference to 

 iron ; and has also found alloys which protect iron in solvents elec- 

 tro-chemically as fully as pure zinc, and yet are not themselves acted 

 on by the solvent. 



He enters into the subject of the specific gravities of the alloys of 

 Zn + Cu and Sn -f Cu minutely, and shows reason to doubt the 

 accuracy of the published specific gravities of most alloys of these 

 and some other classes. 



