ANALYSIS OF CEftTAIN ALLOYS BY MEANS OF THE SPECTKOSCOPE. 499 
Curve 4. 
The range of alloys is the same as those given in the preceding curve ; but the method 
used was that employed in obtaining Curve 2, and it is interesting as illustrating the 
change introduced into the form of the curve by varying the method by which the 
spectral lines were observed. 
Practical Considerations. 
It is impossible to foresee to what analytical operations the new method may be found 
to be applicable ; but as the experiments hitherto have been mainly directed towards the 
development of a new method of assaying gold, it is advisable that attention should be 
limited to the relative advantages of the old and new methods. 
We ascertained by careful experiment that the amount of alloy actually volatilized 
during an observation in no case exceeds O'OOOl grm. ; and it is interesting to compare 
this with the amount of metal usually employed in assaying gold, which varies from 0‘5 
to 1 grm. 
It may be objected that the amount of metal employed in the new method is very 
small ; but granting the accuracy of the method and the homogeneity of the alloy, there 
is of course no reason why the composition of a gold ingot may not be ascertained by 
it as accurately as by the old method. 
It is now well known, as previously mentioned, that the existing method is usually 
accurate to the l0t Q 00 part of the portion of metal operated upon, the process possessing 
in addition to its accuracy many incidental advantages, not the least of which is the 
possibility which it affords of detecting, at different stages of the work, the presence of 
metallic impurities, such as iridium. 
On the other hand, it should be observed that the method now in use comprises six 
distinct operations, and two hours are occupied in ascertaining the final result of the 
assay ; and as it is frequently important to determine the value of an ingot of gold with 
rapidity, it will be obvious that the new method possesses marked advantages in this 
respect, for by its aid a result may be obtained in a few minutes. 
In conclusion, we would submit that experience alone can show whether this new 
process may be made as trustworthy as the existing method ; and we would draw atten- 
tion to the fact that hitherto there has not been absolute identity in the conditions 
under which the several experiments were made; for instance, the intensity of the 
current employed to volatilize the metal varied from time to time ; and this, together 
with other defects, mainly arose from the fact that we have as yet considered the pro- 
blem solely from its scientific aspect, and have not provided ourselves with instruments 
well adapted for satisfying all the conditions which may arise in practice. 
Whether this new method be found preferable to the old one or not, the fact has 
been clearly established that it is possible to detect, by its means, differences in the com- 
position of the gold-copper alloy as minute as the 10 u 00 part of the whole mass. 
