Page:Proceedings of the Royal Society of London Vol 60.djvu/176

Rh metals, one of the two being in each case either silver or copper. It is an extension into temperatures as high as 1100° C., of experiments similar to those at lower temperatures with which we have been occupied for the last seven years. The results of our previous experiments, in which mercury thermometers were used, are published in the ‘Journal of the Chemical Society.’ In the work described in this paper the determinations of temperature were made by means of platinum electrical resistance pyrometers of the Callendar-Griffiths type.

The paper is divided into four sections.

Section I contains a short survey of certain points in the theory of concentrated solutions which bear on the interpretation of the experiments.

Section II is devoted to an account of the experimental method.

Section III contains the results of the experiments in a tabular form, each table being followed by notes and remarks taken from the experimental note books.

Section IV contains the results expressed graphically as complete freezing-point curves, together with a discussion and a statement of the conclusions that can be arrived at from a study of each curve.

If we plot the percentage composition of an alloy horizontally, and the freezing point vertically we get the freezing-point curve. This, for a pair of metals, would consist of two branches, each starting from the freezing point of a pure metal, and descending until they meet in the eutectic point. Our silver-copper curve gives a fair idea of this case.

If the metals A and B form a stable compound C, then the theory as developed by Bakhuis, Rooseboom, and by Le Chatelier makes it probable that the curve will be divided into the systems A C and C B with two eutectic points, and an intermediate summit at 0. This case is well illustrated by a complete freezing-point curve of copperantimony by Professor Le Chatelier, in which two such summits occur.

Another not infrequent case is probably that of a compound, which when molten can only exist in a partially dissociated condition. Our silver-antimony curve resembles such a curve. Other points of Section I will be best deferred to the summary of Section IV.

The alloys, weighing from 200 to 500 grams, were melted in plumbago (salamander) crucibles, placed in one of Fletcher’s blast furnaces.