65 
THE CONSTITUTION OF THE COPPEE-TIN SEKIES OF ALLOYS. 
Sn 45 to Sn 87 into complexes of H and Sn, free from t), and although it will not be 
quite so evident from the photographs, we think we have also eliminated all the 
eutectic from the alloys between Sn 25 and Sn 45. This result was attained by 
maintaining the temperature of the ingots for hours, and, in some cases, for many 
days and nights, at a temperature near 350°. By varying the length of tliis period 
of incubation one can watch the gradual disappearance of the phase to be eliminated 
The constant temperature was that of a bath of boiling mercury, tlie little ingots 
being sealed in glass tubes and suspended in the vapour. The first alloy systeinati- 
cally examined in this way was Sn 50, and the series of photographs Ave publish 
illustrate the changes very well (figs. 84, 91, 92, 93, 94). 
The Sn 50 maintained for some hours at 420° and then chilled (fig. 86), has been 
already described; it contained no H. Fig. 91 is tliat of an ingot that Avas not 
cooled very sloAvly, but was not chilled at all. This section cuts the plates of 'q so 
that they appear as bars. Tlie p has oxidised a good deal before the photogi’aph was 
taken, and it is seen to be margined and traversed by narrow threads of pure white 
H. This small amount of H is Avhat one usually finds when no special pains have 
been taken to complete the reaction by sIoav cooling. 
The next ingot (fig. 92) had been maintained for 10 hours at 380° before chilling. 
The 7) IS now seen to be surrounded by a thick margin of H, and altliough the 
photograph does not perhaps make it evident, the proportion of tin-rich mother- 
substance has decreased considerably. The next ingot AAms maintained for 60 hours 
in the mercury bath at about 350°. It Avill be seen from the photograph (fig. 93), 
that the p is iioav reduced to a feAv spots and lines enveloped in the massive H. 
In order to ascertain Avhether the reaction could be made complete, an ingot was 
boiled for 21 days and nights in the mercury liath. Tliis operation, as fig. 94 shows, 
has removed every trace of r), and very much changed the cliaracter of the masses of 
H. The shape of the H had been hitherto dependent on that of the original p, but 
now the grains of H are independent of each other, and though still rounded they 
are beginning to change into polyhedra with plane faces. It Avould be interesting to 
study the effect of a still longer incubation on the shape of the H. We have isolated 
these little pellets of H and examined them under a low power; they are then seen 
to be crystalline. 
The ingot of Sn 50 (fig. 94) contains around the masses of H a considerable amount 
of tm-iich eutectic, in other words the H does not fill the alloy; consequently, this H 
cannot be exactly CuSn. We there fore examined ingots of Sn 40, 42, 45, as well as 
ingots of Sn 55, 60 and 85, that had all been heated for 21 days in the mercury bath. 
The result showed that all the rj, except mere traces, could he removed from Sn 45, 
but that, although large portions of the section were compact H, yet there were large 
gaps in the H (fig. 95). Ihese gaps appear, however, to be cavities in the ingot, and 
not spaces full of the eutectic. These gaps are numerous in all the alloys, such as 
Sn 45 to Sn 40, when they have been boiled for a long time in mercury ; we think it 
^OL. coil. —A. K 
