Thermoelectricity of Molten Metals. 499 
other portions of the circuit should be affected only by slight 
thermoelectric forces, which remained constant for a con- 
siderable time and which were separately determined. The 
electromotive forces were measured by compensation. 
6. The temperature of the hotter point of contact was 
maintained:—(1) Ina bath of mineral oil of high boiling-point, 
which was kept agitated by a stirrer. In this way a tempe- 
rature of about 380° C. could be obtained. (2) In an air- 
bath, consisting of three concentric iron cylinders, surrounded 
on the outside by a jacket of iron and chamotte, which was 
constructed according to my designs for another investi- 
gation, and which Hhrhardt* has recently described. It 
was heated by means of gas, and permitted the attainment of 
a temperature of 580°. (38) By a brisk current of vapour of 
constant boiling-point, sent through a glass vessel protected 
against external radiation of heat. The substances employed 
were alcohol 80° C., water, xylol 140°5 C., aniline 183° C., 
dimethylaniline 192° C., toluidine 198° C., xylidine 214° C. 
In order to decide with certainty particular questions I re- 
quired constant temperatures, not differing much from each 
other. For the control of other measurements, I further 
employed baths of vapour of benzoic acid 250° C., mercuric 
iodide 357° C., and sulphur 448° C. For still higher tem- 
peratures (up to 980° C.) I employed (4) a muffle. The 
vessels which contained the metal were of earthenware. 
Imagine an earthenware tube inclined some 10° to the hori- 
zontal plane, and provided at both ends with vertical pipe- 
heads. Two such tubes of equal length were placed side by 
side. Hach contained a molten metal. The upper pipe-heads 
were within the muffle, and heated to a higher temperature 
than the lower ones. They were connected by a bridge of 
thick iron-wire or of retort-carbon, by means of which a wide 
thick-walled chamotte-neck passed from the muffle through 
the heating-channel outwards, through which the earthenware 
tubes passed ; the other two pipe-heads were outside the 
mufile, surrounded by an iron box, which was heated by coal. 
The temperature then was maintained as close as possible to 
the melting-point of the more difficultly fusible metal. In 
order to carry the circuit from the molten metal outside the 
muffle, previous experience had shown lead to be the only 
available metal which permitted the reduction of temperature 
to that of the room. The following arrangement was adopted 
in view of its properties :—At the lower end of a thin- 
walled brass-tube of about 12 millim. diameter an iron tube 
* Wied, Ann. vol. xxiv. p, 217 (1885). 
