1874] lU4 [Outerbridge. 



iu an automatic combination of accurately proportioned screws, acting 

 in opposite directions, by which a single motion of the hand sufficed to 

 cause the upper and lower electrodes to approach or recede from the cen- 

 tral line of contact in an equal degree. The electrodes, which consisted 

 of small strips of metal cut to a point, were held by a suitable arrange- 

 ment on the outer circumference of two metallic rings insulated from 

 each other, the upper one slotted to receive a series of twelve electrodes 

 of varying Jcnown fineness, and revolving horizontally, so that each elec- 

 trode might in turn be adjusted to face a single electrode of unknoton 

 fineness fixed on the lower ring. Its object was to admit of the electrodes 

 being separated to any desired extent, while preserving the line of vision, 

 through the spectroscope, directed to the centre of the spark. This is a 

 point of much importance. 



A systematic series of experiments was now commenced, in which the 

 behavior of the more volatile metals was at first studied, viz : Lead, 

 Zinc, Bismuth, Tin, Antimony, Cadmium, Mercury, Aluminium, &c. 

 All these give more decided spectra than the less volatile precious metal?, 

 and some interesting results were noticed. Approximate illustrations cf 

 some of these spectra are appended. 



Proceeding to the examination of gold alloys, and starting with base 

 poles — making the lower pole 250 fine and the upper pole 500 fine — the 

 gold lines from the upper half were both longer and brighter. Now sub- 

 stituting in place of the 250 pole one 700 fine, the lower half showed the 

 brighter gold lines. Then, changing the 500 pole for one 800, the bright- 

 ness of the gold line was again reversed. This alternating effect may be 

 continued, decreasing in degree as the fineness of the poles approach more 

 nearly together, until both poles are of the same fineness, when the lines 

 will be equal in length and intensity. 



These experiments proved satisfactorily that comparatively wide varia- 

 tions in the composition of gold alloys were discernible. I now had pre- 

 pared at the Mint a series of graduated alloys of more approximate fine- 

 ness, viz : 



GOLD AND COPPER. GOLD, SILVER AND COPPER. 



938. 940.1 



917. 918.7 



906. 866.8 



888.3 888. 



883.5 884.1 



876.5 883. 



These alloys were carefully prepared and assayed closely. 



With one electrode pure gold and the other 938 fine, the difference be- 

 tween the respective spectra was of course very marked, the copper lines 

 appearing in the one and not in the other. Substituting for the pure 

 gold the alloy 876.5, the difference was still very marked, for, although 

 both gold and copper appeared in each, the copper lines were much 

 brighter and somewhat longer in the baser alloy, while the gold lines were 



