go The Spectroscope in Mint Assaymg. | January, 
platinum wicks. A series of solutions, each one half the 
strength of the preceding one, were prepared from a number 
of metallic chlorides. ‘The spectrum in connection with the 
positive pole was continually observed while increasingly 
concentrated solutions were brought in succession into the 
action of the spark, until the lines of the substance were 
clearly visible.’ If a sceptical mind refuses to believe the 
results of Cappel, who tells us that r-600th of a milli- 
gramme (1-38,S0o0th of a grain) of nickel will just write the 
signature of that metal, what will he say when, glancing 
at table B appended hereto, he finds the statement that 
1-60,000th of a milligramme (1-3,880,oo0th of a grain) of 
nickel will sign its name in brilliant characters? And yet 
the author does not hesitate to say that even a smaller 
amount of this metal will show a spectrum, for it must be 
remembered that in these experiments a much stronger 
spark was used than was necessary to show a visible spec- 
trum. When reduced to a minimum, as was done in the 
case of the miniature Leyden jar, which still gave a distinct 
spectrum, the loss in weight after 3000 sparks, for silver, 
copper, and tin, was absolutely inappreciable on the balance. 
The table of loss shows another curious and unexpected 
result, viz., that the loss in weight of the volatile metals 
very slightly exceeds, and in some cases does not equal, the 
loss of the less volatile metals. Thus, in three different ex- 
periments of 3000 sparks each, copper loses but o'r milli- 
gramme, while gold loses 0°5 milligramme. 
An unexplained anomaly was also noticed in relation to 
the sensitiveness of the spectroscope to the metals present 
in small proportion. Although Mr. Cappel has shown that 
1-4000th of a milligramme of gold will show a spectrum (it 
is even less than 1I-6000th of a milligramme, according to 
an experiment performed by the method described above) 
yet a comparatively large proportion of gold may be present 
in an alloy, the presence of which will not be indicated at 
all by the spectroscope. 
In a slip composed thus—Silver 708 parts, copper 254 
parts, gold 38 parts—the spectra of szlver and copper are 
alone visible. 
In fact, in a base alloy of gold and copper containing 
from 20 to 25 per cent of gold, the gold spectrum is barely 
visible; while in a fine alloy of gold and copper it was 
found that 1 per cent of the latter suffices to show the 
copper spectrum. Also in an alloy of nickel and copper 
containing 25 per cent of nickel, its spectrum is scarcely 
visible. Its seems evident, therefore, that the spark selects 
the more volatile metal as its vehicle. 
