Outerbridge.] 1^^ [May 15, 



The general principle was satisfactorily proved, however, that where 

 two alloys of different grades are subjected to this treatment, the gold 

 lines of the baser compound are noticeably the fainter of the two, and, 

 what is more important, they may be reduced in length by separating 

 the poles, until they disappear. 



This points to the possibility of the future application of Spectrum 

 Analysis to Assaying, at least as a test method. For, if an alloy of abso- 

 lute known fineness wfere adopted as one electrode, and an ingot-slip 

 assayed by the old process to an equal grade of fineness were inserted as 

 the opposite electrode, in case the assay were correct, the gold lines in 

 both sections of the spectrum should appear of equal brightness, and 

 more especially, should begin to recede from the central line of the spec- 

 trum at the same moment, and should disappear at the same moment. 



The spectra being inevitable natural effects of physical causes, a varia- 

 tion between two specimens of supposed equal fineness would, in theory, 

 be necessarily indicated by the respective lines failing to correspond in 

 their reciprocal action. To use the method as a means of original assay, 

 it would be necessary, among other things, to construct scales of delicate 

 measurement which, if possible at all, could only be done by a long 

 course of laborious investigation. 



The experiments of which the foregoing is a resume, involved many 

 matters of practical detail to which it is unnecessary to allude, and having 

 been conducted at short notice and within the brief period of four days, 

 they must be considered as simply preliminary. 



Respectfully submitted, 



Alex. E. Outerbeidge, Jr. 



Philadelphia, May 5t7i, 1874. 

 Wm. E. Du Bois, Esq., 



Assayer U. S. Mint. 



Sir : — Since submitting to you my report of the 30th of October last, I 

 have continued at intervals the investigation of the "Electrical Spectra 

 of Metals," with a view to the practical application of the spectroscope 

 to Mint assaying. 



Having repeated and proved the correctness of the experiments pre- 

 viously recorded, using a three-prism spectroscope and an induction coil 

 capable of throwing an eight inch spark, (kindly furnished me by Dr. R. 

 E. Rogers of the Medical Department of the University of Penna.) I found 

 it necessary to devise a special apparatus for manipulating the electrodes 

 when under examination. This was made for me by Mr. Saml. James, 

 the machinist in the Mint, and admirably fulfilled its object. A photo- 

 graph and description of it are appended hereto. Its peculiarity consisted 



