52 PROCEEDINGS OF THE AMERICAN ACADEMY 



by him from M. Moissent, of the Imperial School of Mines, 

 Paris, giving an account of a new gas-engine, invented by M. 

 Lenoir of that city. He also gave some further details con- 

 cerning the frozen well, at Brandon, Vermont. 



Four hundred and eighty-sixtb meeting. 



September 11, 1860. — Monthly Meeting. 



The President in the chair. 



Professor Horsford, chairman of the Rumford Committee, 

 laid upon the table the dies for the Rumford medal, received 

 from the United States Mint, in pursuance of a vote of the 

 Academy at the last Anniversary Meeting. And they were 

 deposited in the iron safe of the Academy. 



Professor Horsford submitted a memoir on the relations 

 of the salts of zinc and alumina to those of soda and potassa. 



Messrs. Charles W. Eliot and Frank H. Storer presented 

 the two following notes, supplementary to their Memoir upon 

 the Impurities of Commercial Zinc. 



I, On the Amounts of Lead contained in some Silver Coins. 



From our experiments upon the impurities of commercial zinc,* 

 we found that this metal almost invariably contains lead. In the 

 preparation of silver at the United States Mint, zinc is used for the 

 purpose of reducing chloride of silver,t and a sample of zinc similar 

 to that used at the Mint, which we examined, yielded half of one per 

 cent of lead. The question naturally suggested itself whether lead 

 might not thus find its way into American silver coin, and to deter- 

 mine this point we have analyzed several American coins, as specified 

 in the following table ; for the sake of comparison we subsequently 

 examined the other coins therein enumerated. 



* Memoirs of the American Academy, 1860 [n. s ], VIII. 57. 



t Booth and Morfit's Smithsonian Report on Recent Improvements in the 

 Chemical Arts, (Washington, 1851,) p. 56. Compare "Wilson's Report on the New 

 York Industrial Exhibition, in Dingler's Polyt. Journal, 1855, CXXXV. 119. 



