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(1) Proc. Roy. Irish Academy, Vol. II., 1891.

(2) Ramsay and Eumorfopoules, Phil. Mag., XLI, page 360, 1896.

(3) “ Electrician” (London), January 1st, 1909.

This instrument was originally designed by Prof Joly, F.R.S., for determining the melting points of minerals, salts, metals, and alloys. The special feature of the apparatus is that it only requires a very small quantity of the substance whose melting point is to be determined, and therefore the substance may be obtained in a high state of purity ; or, in the case of minerals, fragments can be chipped off museum specimens without destroying their value.

The linear expansion of a strip of platinum with temperature is the principle upon which the working of the instrument depends. The substance to be investigated is placed in the centre of this platinum strip, which is then heated by the passage of an electric current until the substance melts. The length of the strip at this moment is a measure of its temperature, and therefore of the melting point of the substance.

The platinum strip and the substance to be melted are shielded from draughts by a hood. A. microscope whose focussing adjustment is made by means of Lucas’s Patent Slow Motion Mechanism is focussed on the specimen.

The actual extension of the platinum strip is measured by a micrometer screw, by which it is possible to measure an extension of the strip of 0'0005 min.

A current of about 6 amperes is required to obtain a temperature of 1,400° C., and the platinum strip glows quite uniformly to within a few millimeters of the supporting clips, owing to the fact that the ends of the strip are tapered. The strip begins to suffer permanent elongations only at about 1,500° C. It is possible to detect differences of 1° C. at 1,000° C.

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