Thermoelectric Position of Platinoid. 165 



galvanometer-mirror with the smallest possible speck of shellac 

 varnish, the greatest care being taken not to varnish any part 

 of the spider-line. When the varnish has dried, the mirror 

 can be lifted up by the spider-line ; caution being used at the 

 moment of raising the one mirror off the surface of the other, 

 on account of the vacuum which is liable to be formed at the 

 moment of separation. The mirror should be allowed to hang 

 on the fibre inside a glass beaker for twenty-four hours at 

 least, as the spider-line stretches considerably for some time 

 after the weight comes on it. A spicier-line which will carry 

 a galvanometer-mirror and magnet weighing - 2 gram may 

 have, according to an estimate made by one of the present 

 writers, about T Jq of the torsional rigidity of a single cocoon- 

 silk fibre. 



For the heating of the junctions, a number of glass vessels 

 were blown, resembling the flasks, with neck and condensing- 

 tube, used for fractional distillation, but with the condensing- 

 tube projecting upwards into the air, so that the steam of a 

 liquid boiling in the flask ran back into the flask on being 

 condensed. Into the shorter neck of the flask was introduced 

 a cork, which carried the thermo-j unction and a mercurial 

 thermometer ; the thermo-j unction being loosely bound to the 

 bulb of the thermometer, or, at any rate, kept in close contact 

 with the middle part of the thermometer-bulb. The cool 

 junction was bound to the bulb of a second thermometer, 

 which dipped into a vessel containing water at the tempera- 

 ture of the laboratory. The water was kept thoroughly 

 stirred from top to bottom by a properly arranged stirrer. 



In the heating-flasks the vapours of the following liquids 

 were used : — alcohol, w T ater, chlorobenzol, aniline, methyl 

 salicylate, and bromobenzol*. The liquids were boiled 

 vigorously, and the temperatures of the vapours were deter- 

 mined by means of the mercurial thermometer. Both the 

 mercurial thermometers were compared directly with the air- 

 thermometer f. The obtaining of a set of points of tempera- 

 ture by this means was very satisfactory in every case except 

 that of the liquid of highest boiling-point — bromobenzol. In 

 this case a curious phenomenon was observed if. In spite of 

 the fact that the vapour of the substance was rushing strongly 

 into the condensing-tube, and, indeed, out into the open air 

 at an elevation of two feet above the surface of the liquid, it 

 was found exceedingly difficult to keep the temperature of the 

 various parts of the boiling flask anything like uniform. The 



* Ramsay and Young-, Cliem. Soc. Journ. (Trans.), 1885. 



t J. T. Bottomley, Phil. Mag. August 1888. 



X Perhaps due to want of purity of the substance. 



Phil. Mag. S. 5. Vol. 28. No. 172. Sept. 1889. 



