32 MEASUREMENT OF HIGH TEMPERATURES. 
After these publications Deville and Troost made no further impor- 
tant contributions to high temperature thermometry for five years. 
The subject occupied Kegnault, 1 who proposed two methods. The 
first of these small flasks of iron or porcelain are partially charged 
with mercury, and closed above with a loosely -fitting valve or stopper. 
These are exposed at the temperature to be measured, and this is 
calculated from the weight of mercury left after cooling. The other 
method, being a displacement method, will be described below. 
Shortly after this a series of very painstaking attempts in the measure- 
ments of high temperatures were made by Schinz. 2 Curiously enough, 
these papers, which contain a series of experiments admirably correct 
in principle, are but little known. Schinz, after endeavoring in vain to 
utilize the principles of heat conduction in practical pyrometry, and 
after testing Kegnault's displacement method with unfavorable results, 
applies the thermo-electric methods of Pouillet and of Becquerel. 
Sehiuz's air-thermometer bulb is a huge iron cylinder, from the center 
of one end of which an iron capillary tube passes to the mauometric ap- 
paratus, while an iron tube for the insertion of the junction of the 
thermo-couple projects inward to the center of the figure through the 
other end of the cylinder bulb. In this respect Schinz's thermometer is 
unique, being the only form of re-entrant bulb hitherto devised. The 
great advantage of this form of bulb, which, quite independently of 
Schinz, has been perfected in my experiments, will be emphasized below 
(Chap. IV). Nitrogen is the thermal gas in Schinz's work, and the cali- 
brations are carried as far as 1,000°. Giving him full credit for correct- 
ness of method and for the assiduity with which he endeavored to carry 
it out, Schinz's apparatus was doomed to fail because of its impractical 
clumsiness of construction, to say nothing of the permeability of iron at 
high temperatures. It is not possible to make much definite progress 
in the measurement of high temperatures with an apparatus which falls 
short of the conditions of facility and certainty of manipulation. I shall 
revert to these measurements. For the special conveniences of the in- 
vestigating chemist, . Berthelot 3 devised an apparatus intended to be 
compact and very sensitive, and provided with an easily adjustable em- 
piric scale. His instrument is based on the expansion of air and grad- 
uated by boiling points. Another instrument by Zabel 4 is so adjusted 
as to ring an electric bell at any giveu temperature. It is perhaps ex- 
pedient to advert in this connection to the thermometers of Weinhold 5 
and of Crafts, 6 both of which are constructed on Jolly's 7 plan, but so ad- 
justed that the conditions of constant volume are secured by the aid of 
1 Regnault: Ann. ch. et phys., 3d series, vol. 63, 1861, p. 39. 
2 Schinz: Dingler's Jour., vol. 177, 1865, p. 85 ; ibid., vol. 179, 1866, p. 436. 
3 Berthelot: Ann. ch. et phys., 4th series, vol. 13, 1868, p. 144. 
4 Zabel : Dingler's Jour., vol. 195, 1870, p. 236. 
5 Weinhold: Pogg. Ann., vol. 149, 1873, p. 186. 
6 Crafts: Ann. de Chim. et de Phys., 5th series, vol. 14, 1878, p. 409. 
7 Jolly : Pogg. Ann., Jubelband, 1874, p. 82. 
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