Outerbridge.] 17U [May 15, 



gold may be present ia an alloy, the presence of which will not be indi- 

 cated at all by the specti'oscope. 



r Silver, 708 parts. 



In a slip composed thus : v < Copper, 254 " 



the sj)ectra of silver and copper are alone visible. (^Gold, 38 " 



1000 



In fact, in an alloy of gold and copper containing from 200 to 250 parts 

 of gold, the gold spectrum is barely visible. In the case of gold con- 

 taining copper, it was found that one per cent, of the latter sufficed to 

 show the copper spectrum ; likewise in an alloy of nickel and copper 

 containing 20 per cent, of nickel, its spectrum is not visible. 



If the spectroscope fails to reveal the presence of anything less than 

 200 parts of gold in a base alloy, even a theorist must admit that one could 

 scarcely expect to be able to discriminate with certainty a variation of 

 To 00 in a fine alloy. 



It is not impossible that future discovery may succeed in explaining 

 this anomaly, in harmonizing the apparent inconsistencies, in eliminating 

 the sources of error, and in reducing the operation to practicable cer- 

 tainty, but in the state of spectroscopic science as it now exists, so far as 

 I have been able to perceive, I have arrived at the opinion, not without 

 regret, that assaying by means of spectrum analysis is impracticable for 

 the purpose of Mint operations. 



In conclusion, it should be stated that the principal part of my work 

 was performed at the University of Pennsylvania, with the benefit of the 

 excellent appai-atus and appliances afforded in the new and magnificent 

 college building. For this privilege, and also for many valuable sugges- 

 tions and for personal favors, I desire to acknowledge my indebtedness to 

 Professor Geo. F. Barker of that Institution. 



Very respectfully, yours, 



Alex. E. Outerbkidge. Jr. 



TABLES. 



First column shows the weight of the metallic-electrodes in milligrams 

 before passing the spai-ks. 



Second column shows the weight after passing 3000 sparks. 



Third column shows total weight of metal volatilized (in fractions of a 

 milligramme). 



Fourth column shows the amount of metal volatilized by each spark 

 (in fractions of a milligramme). 



