DuBois.] 1G2 [May 15, 



ELECTRICAL SPECTRA OF METALS. 



Results of an Examination as to the Practicability of Assay- 

 ing Metals used in Coinage, by means of Spectrum Analysis, 



MADE in and for THE AsSAY DEPARTMENT OF THE U. S. MiNT AT 



Philadelphia. 



By Alex. E. Outerbridge, Jr. 



Communicated to the American PMlosopJdcal Society, 5y Mr. W. E. Du 

 Bois, Assayer of the Mint, May 15th, 1874. 

 It must have occurred to many, when this brilliant method of scientific 

 research succeeded in detecting the presence of metals, in any given sub- 

 stance, even to an infinitesimal nicety, that the next step must be to de- 

 termine the proportion of such presence ; in other vrords, the qualitative 

 must certainly lead to the quantitative, as in other chemical processes. 



The Annual Report of the Royal Mint at London, for 1872, (dated 15th 

 of April, 1873,) contains an official memorandum of Mr. W. Chandler 

 Hoberts, Chemist of the Mint, from w^hich it appears that he was engaged 

 An examining this subject, at the suggestion of, and in connection with, 

 the distinguished spectroscopist and astronomer, Mr. J. Norman Lockyer. 

 No decided results had been reached ; but Mr. Roberts concluded by ex- 

 pressing the belief "that every effort should be made to render the in- 

 strument serviceable in the operations of minting." 



The present modes of assaying gold and silver, both in alloys and in 

 ores, have been brought to such perfection, such_ accuracy, delicacy and 

 dispatch, that it seemed almost a matter of regret to have them super- 

 seded or disturbed. And yet, there is something captivating in the idea of 

 a determination, as it were by a flash of lightning, or in the twinkling uf 

 an eye, what proportion of gold or silver is present, in any bar, or coin, 

 or native ore. It therefore seemed desirable that our own Mint should 

 maintain its character for examining and adopting real improvements, 

 and not to wait indolently to hear what might be done abroad. 



One of the assistants in the Assay Department, Mr. Alexander E. Out- 

 erbridge, Jr., had for several years given special attention to spectrosco- 

 pic studies, both in theory and in practice ; and to him therefore, the 

 subject was committed ; with what propriety, and what success, will 

 sufficiently appear from what he has written. This will be found in the 

 two following communications addressed to the Assayer. 



The details he has given are well worth a careful study ; but we can- 

 not help noticing, in a few words, the astonishing paradox at which his 

 experiments arrive ; namely, that this method is, in one respect, by far 

 too sensitive and minute ; and in another respect, far from being minute 

 enough, to serve the uses of assay. It was worth all his patient labor 

 many times over, to come to this conclasion ; as we miist come in the 

 present state of this branch of science. And it is likely, that the natural 

 and necessary imperfections of metallurgy, the want of complete atomic 

 homogeneity in the mixing of metals, will forever prevent the spectro- 

 scope from taking the place of the present methods of assay. 

 As Mr. Outerbridge has been careful to give facts rather than suppo- 



