1875.] The Spectroscope in Mint Assaying. QI 
If the spectroscope fails to reveal the presence of anything 
less than 200 parts of gold in a base alloy, even a theorist 
must admit that one could scarcely expect to be able to 
discriminate with certainty a variation of I-r0,oooth in a 
fine alloy. 
For the foregoing reasons, the conclusion seems inevitable, 
that in the state of spectroscopic science as it now exists, 
assaying by means of spectrum analysis is, for the present, 
impracticable for the purpose of Mint operations. 
Although these experiments have resulted negatively from 
the utilitarian standpoint from which they were undertaken, 
it is hoped that they may prove not altogether without value 
in a more general point of view. The fact that bam 
proportions of composite substances may be recognised a 
all, even to a rough degree, cannot but be regarded as a 
first step. All observations bearing upon the action of the 
spectral lines in indicating such proportions are at least 
worthy of being recorded. Not the least curious of these 
incidental observations is the fa¢t that while the spec¢tro- 
scope is sensitive to the minutest fraction of a grain of gold 
in the pure state or in solution, it fails to rev eal the presence 
of a much larger proportion in a base alloy. Another is the 
fact that while the spark appears to select for its vehicle of 
transmission the more volatile metal in an alloy, and would 
thus seem to vaporise a greater quantity of the volatile than 
of the non-volatile component, yet, in point of fact, the loss 
of weight by such volatilisation is in some instances mucii 
less in the former case than in the latter. 
he rationale of these apparent paradoxes is not at present 
evident, but if we may judge by former experiences in which 
preblems even more mysterious have been resolved by study, 
we are warranted in anticipating that when a large number 
of observations, to be made perhaps by many experimenters 
groping in the dark, shall be collated, the true scent may of 
a sudden be struck which shall discover the desideratum of 
quantitative spectrum analysis. 
‘TABLES. 
The first column shows the weight of the metallic elec- 
trodes in milligrammes before passing the sparks. Second 
column shows the weight after passing 3000 sparks. Third 
column shows the fofal weight of metal volatilised (in frac- 
tions of a miligramme). fourth column shows the amount 
of metal volatilised by cach spark (in fractions of a milli- 
gramme). f2fth column shows the amount of metal vola- 
tilised by each spark in fractions of a grain troy. 
