THE CONSTITUTION OF THE COPPER-TIN SERIES OF ALLOYS. 
3 
advance beyond that of December, 1901, although the diagram (Plate 11) now given 
is in some minor points more accurate than the earlier one, and a change has been 
made in the notation. The main purpose of the present paper is to give the evidence 
for the correctness of our views, evidence which is largely drawn from the photographs 
of the chilled ingots. 
The photographs are reproduced in Plates 1 to 9, containing figs. 1 to 101 arranged 
in order ; opposite each plate is a table giving a brief description of the figures 
contained in it, the composition of the alloy, the method of etching the ingot, and 
the magnification employed in taking the photograph. 
Before considering the photographs it will be necessary to discuss the cooling 
curves of Plate 10 and the equilibrium diagram of Plate 11. We sliall thus be able 
to present an outline of our conclusions which will, we hope, render the bulk of the 
evidence, which is given further on, more intelligible. We think that a reader 
ivishing to understand the results of our ivork without desiring to weigh the evidence 
minutely woidd find Section /., and an examination of the 'phates and gohotogrcophs 
referred to in Section /., cdmost sufiicient for his purpose. 
The Cooling Curves. —(Plate 10.) 
Although the pyrometric work of Roberts-Austen and Stanseield gave us most 
valuable suggestions, we did not find it possible to use it quantitatively. This was 
partly due to the small size of their published curves, and partly to their being 
constructed on a thermometric scale different from the one employed by us. We 
therefore detei'inined to repeat a good many of the cooling curves and to reconstruct 
the thermal diagram of the alloys. Plate 10 gives the more important of the cooling 
curves obtained by us, but we have in addition traced the cooling curves of alloys 
with more tin. Our curves are very similar to those of Roberts-Austen and 
Stanseield, and we are not prepared to say that they contain any additional 
information, but they are in a form convenient for use with the present paper. They 
were traced by means of a platinum-resistance pyrometer and a Callendar recorder, 
in which a pen, controlled by the pyrometer, writes on a rotating drum. 
In Plate 10 the horizontal ordinate is time, and it is reckoned from left to right, 
the vertical ordinate being temperature reckoned downwards. A scale of Centigrade 
degrees is placed at each end of the diagram, which will enable the temperature of 
an alloy at any point on its curve to be read off. It may be noticed that equal 
vertical distances do not quite correspond to equal ranges of temperature, but that 
the scale becomes more open as the temperature falls. This pecidiarity arises from 
the curves having been traced automatically on the platinum scale. The curves are 
an exact copy half-size of those traced on the recorder.' The number at the head of 
each curve indicates the atomic percentage of tin in the alloy. In tracing a curve a 
mass of about 300 grammes of alloy was melted in a double or treble crucible and 
allowed to cool spontaneously with the pyrometer immersed in it. The time of 
B 2 
