S4 \V. Sturgeon, Esq., on the 



if any iron could possibly have entered the alloy, its quantity 

 must have been too small to cause the high degree of mag- 

 netic action which the specimen exhibited. 



36. On comparing this alloy of silver and copper with the 

 alloy of iron and antimony, in which the weight of the latter 

 metal is only about twenty times that of the iron (24), some 

 very remarkable circumstances present themselves. In the 

 former alloy, where no iron can be detected by the usual che- 

 mical tests, we have a metal whose magnetic action is, at 

 least, twice as powerful as that displayed by the alloy of iron 

 and antimony, an alloy of which iron constitutes a very con* 

 siderable proportion, and whose presence, had it not been 

 previously known, could have been detected by the humblest 

 test for ferruginous matter. These parallel experiments tend 

 to shew either that an alloy of pure silver and pure copper is 

 magnetic, or that the magnet is a better test for the presence 

 of minute portions of iron, in such alloys, than any hitherto 

 known in chemical manipulations. 



37. I regret that another piece of unmagnetic silver has 

 not yet fallen in my way, to enable me to make further in- 

 vestigations on this curious subject. But I am in hopes of 

 obtaining unequivocal results before the second part of this 

 memoir is brought before the Society. 



38. With respect to brass, one of our most important al- 

 loys, I have found it to be highly magnetic in a great number 

 of cases, viz., in all the various states of newly cast brass, 

 brass-wire, and sheet-brass, as well as in several articles of 

 brass manufacture. But, from the very gi'eat difference in 

 the degrees of magnetic action displayed by different speci- 

 mens of this beautiful alloy, and the total absence of that 

 action in others, there has appeared to me a high degree of 

 probability that the magnetism displayed by brass is due to 

 accidental portions of iron in the alloy. 



39. Cavallo discovered that in magnetic brass the action 

 was more powerful in large pieces than in small ones. This 

 fact I have also observed in several specimens that I have ex- 

 amined. The reason seems to be, that in the larger pieces a 



