60 I'HILOSOPHICAL TRANSACTIONS. [aNNO 1786. 



gold, both soft and hammered ; a mixture of gold and silver, both hard and soft; 

 and another mixture of a great deal of silver, a little copper, and a less quantity 

 of gold, either before or after hammering, had not the least action on the mao-- 

 netic needle. Platina was the metal he last examined, and the experiments made 

 with it seem to deserve particular attention, as they showed sometimes some small 

 degree of magnetism in this substance. 



As far as I could observe, says Mr. C, those pieces which would not acquire 

 any magnetism by hammering, had not a very shining appearance before the ham- 

 mering, though afterwards they could not be distinguished from the others by 

 their appearance ; and they seemed not to spread under the hammer so easily as 

 the others. In general 3 or 4 strokes are sufficient to render a grain of platina 

 evidently magnetic, but about 10 strokes give it the full power it is suscepti- 

 ble of. 



If it be true, as those experiments seem to prove beyond a doubt, that mag- 

 netism may exist, or may belong to other substances, independent of iron, it 

 must follow, that the attraction of a few particles of an unknown substance by 

 the magnet is not a sure sign of the presence of iron. Hence those substances, 

 which hitherto have been considered as containing ferrugineous particles, for no 

 other reason but because the magnet attracted a small quantity of them, must be 

 considered as dubious ; and the conclusion of the existence of iron should not be 

 admitted, except when those particles, which have been separated by the magnet, 

 appear to be iron by some other trial ; for though it is true, that iron is always 

 attracted by the magnet, yet it does not hence follow, that whatever is attracted 

 by the magnet must be iron. After scrutinizing this matter by still further ex- 

 periments, Mr. C. concludes : It seems therefore to be demonstrated, as far as 

 the subject will admit of demonstration, that the magnetism acquired by brass, 

 when hammered, is not owing to iron contained in it ; and consequently that 

 magnetism, or the power of being attracted by, and attracting, the magnet, may 

 exist independent of iron. 



In the course of my experiments on the magnetism of brass, I have twice 

 observed the following remarkable circumstance: A piece of brass, which 

 had the property of becoming magnetic by hammering, and of losing the 

 magnetism by softening, having been left in the fire till it was partially melted, 

 I found, on trial, that it had lost the property of becoming magnetic by ham- 

 mering; but having been afterwards fairly melted in a crucible, it thereby 

 acquired the property it had originally, viz. that of becoming magnetic by 

 hammering. I have also often observed, that a long continuance in a fire so 

 strong as to be little short of melting hot, general diminishes, and sometimes 

 quite destroys, the property of becoming magnetic in brass. At the same time 

 the texture of the metal is considerably altered, becoming what some workmen 



