654 
ME, J. NORMAN LOCKYEE ON SPECTRUM-ANALYSIS 
II. MECHANICAL MIXTURES. 
The mechanical mixtures experimented on in continuation of the researches referred 
to in my previous communication were prepared in the following manner. 
Method employed in preparing mixtures. 
A quantity of the larger constituent, generally from five to ten grammes, was weighed 
out, the weighing being accurate to the fraction of a milligramme ; and the requisite 
quantity of the smaller constituent was calculated to give, when combined, a mixture of 
a definite percentage composition by weight (this being more easily obtainable than a 
percentage composition by volume). 
The quantities generally chosen were 10, 5, 1, and 0T per cent. 
In a few cases with metals known to have very delicate spectral reactions a mixture 
of O'Ol per cent, was prepared. 
The larger constituent was then introduced into a small crucible (the bowl of a common 
clay tobacco-pipe). A tube conveying a stream of pure dry hydrogen was introduced 
into the mouth of the crucible, and the metal heated by a Bunsen burner. 
As soon as it was melted, the metal, the spectrum of which was to be examined, was 
introduced in fragments, the hydrogen stream being kept up, and the heat raised if 
necessary until the last added metal had melted. When this had taken place, the fused 
mixture was agitated by rapidly shaking the crucible, or by causing the hydrogen to 
bubble through the melted mass. 
When the mixing was judged to be complete, the mass was poured out. On cooling, 
a point was cut from it and placed in the spark-stand, the opposite pole being made of 
the metal which constituted the bulk of the mixture. Thus an alloy of 90 parts tin 
and 10 parts cadmium would have a tin pole opposite, and one of 90 parts lead and 10 
zinc a lead pole, and so on. 
It is important that each electrode of a mixture should have its corresponding elec- 
trode of the pure metal which exists in the greatest quantity in the mixture, as when 
the spectrum is observed the long and short lines of this constituent are seen stretching 
from top to bottom of the spectrum, the longest lines being continuous across, while the 
lines of the smaller constituent are seen only at the top or bottom of the spectrum, 
according to the place occupied by the mixture in the spark-stand. 
Observations. 
The observations thus made have been recorded in the accompanying maps* in the 
following manner: — First the pure spectrum of the smallest constituent has been 
observed, and the lines laid down from Thalen’s map generally. 
The mixture containing the greatest percentage of the substance whose spectrum is 
to be studied is then inserted in the spark-stand with its opposite electrode of the sub- 
stance with which it is mixed, and the spectrum observed. This process is repeated 
until the lowest percentage is reached. 
* These maps were exhibited to the Society, but they have not been engraved. 
