482 
ME. J. NOBMAN LOCKYEB ON SPECTBUM- ANALYSIS 
to notice the following additional phenomena, in which a change in the lines which 
remained was brought about by a change of composition. 
I. The lines varied in their lengths as the percentage of the element to which they 
were due varied. 
II. Some of the lines appreciably varied in their thickness and brightness, or both, 
in the same way. 
III. In cases where the brightness of a line was estimated through a considerable range 
of percentage composition by comparison with an air-line, the latter was observed to grow 
faint and then to disappear when the brightness of the line compared with it increased. 
IV. In cases where the brightness or thickness of the line of one element was esti- 
mated by comparison with the adjacent line of the other constituent of the alloy, the 
point of equal brightness was observed to ascend or descend (I used this method in 
order to avoid the uncertainty of micrometric measurements of the tips of the lines in 
consequence of their variation in length due to the unequal action of the spark). 
V. In some cases where the percentage of a constituent was so small that none of its 
lines were visible, there yet seemed to be an effect produced upon the lines of the 
other constituent as compared with those of the spectrum of the same vapour of the 
opposite pole. 
These conclusions were derived from observations of the alloys which I had made in 
the manner indicated in my second paper ; and I saw that it would be important to 
observe series in which the change of percentage composition between the specimens 
was not so great, and of which actual assays had been made. 
I therefore begged Mr. C. Freemantle, the Deputy Master of the Mint, to allow me 
the use of specimens of the gold-copper and silver-copper alloys prepared for the coin- 
age, as in them I had exactly what the research required — namely, ranges with small 
variations and of undoubted accuracy. I have here to express my deep obligations to 
that gentleman, who at once, with the greatest promptitude and courtesy, acceded to a 
request made to him in the interests of science. 
Before, however, I proceed to consider the cases of the Mint alloys, it will be well to 
briefly notice some experiments with alloys in which the variations in the proportions 
of constituents were greater. 
As an instance of a moderately small difference, an attempt was made with a portion 
of a half-sovereign to which t^o of its weight of copper was added. This was com- 
pared with another portion of the same coin ; but no difference was detected, possibly on 
account of a failure in making an alloy on so small a scale without some loss of the 
smaller and more oxidizable constituent. 
An alloy of 5'5996 grms. lead and 0‘6221 grm. silver was then made, the silver being 
dissolved in the lead, which was fused in a bent hard-glass tube in a current of hydrogen. 
The percentage composition of this alloy was 89 per cent, lead and 11 per cent, silver. 
The silver lines at w. 1. 5470, 5464, 5209 were recognized in its spectrum, and another 
line at 5401 was uncertain. 
