Magnetic Characters of Metak^ ^'c. 89 



the mass, its alloy with zinc will be perfectly neutral to the 

 magnet.* 



55. The neutralization of magnetism in iron by alloying 

 it with zinc is a fact of high importance in the contemplation 

 of metallic magnetism ; and especially the magnetism of 

 brass and other alloys, in which zinc forms a considerable 

 proportion. For it is highly probable that, since zinc smothers 

 the magnetic influence of large proportions of iron, a con- 

 siderable quantity of the latter metal might enter the com- 

 position of brass, without rendering it palpably magnetic. 

 Such, in fact, would absolutely be the case, provided the 

 alloy were perfect, and that the copper had no influence on 

 the magnetic condition of the combined iron and zinc. 



56. To satisfy myself on this point, I have subjected to 

 chemical analysis some of those specimens of brass which 

 had been found to be highly magnetic ; and, as far as I have 

 proceeded, there appears no reason to suppose that the mag- 

 netic powers they displayed were due to iron in their com- 

 position. Indeed, I am now inclined to embrace the opinion 

 of Cavallo (6, note), that the magnetism of brass is not due 

 to ferruginous matter, but depends upon a suitable arrange- 

 ment of the particles of its proper constituent metals, copper 

 and zinc. Nor do I believe that brass generally, as it leaves 

 the foundry, contains any notable quantity of iron. I have 

 analysed many specimens, both magnetic and unmagnetic, 

 and the traces of iron, where any were discoverable, were 

 very minute, and as frequent in the one kind as in the other. 

 It is true that some specimens of brass contain more than 

 an average proportion of iron ; but it is a curious fact that 

 these specimens are not those which display the greatest 

 magnetic powers. 



57. We learn, also, from these facts, that the demagnet- 

 izing powers of antimony and zinc will necessarily prevent 

 the detection of small proportions of iron in those metals, 



* Since this paper was read, I have ascertained that an alloy of iron and 

 zinc in the proportion of 1 to 7 respcctlTely, is quite destitute of magnetic ac- 

 tion. 



