38 MEASUREMENT OF HIGH TEMPERATURES. 
To obtain the high temperatures in question retort carbon is burned in 
an air-blast. The displacement method shows that oxygen, nitrogen, 
sulphurous acid, and even carbonic dioxide are stable at 1,700°. Plati- 
num absorbs much oxygen and must be saturated with it before the ther- 
mal measurements are commenced. On the other hand, chlorine, bro- 
mine, iodine, carbonic oxide, steam, and even hydrochloric acid are more 
or less dissociated. Following these researches into further conse- 
quences, Meyer and his pupils 1 determine the vapor density of zinc, prov- 
ing that all known metallic vapors are monatomic, and they even meas- 
ure 2 the vapor densities of antimony, phosphorus, and arsenic, at 1,437°. 
These brilliant researches contain the most advanced work thus far 
done on the subject of high temperatures, and it is upon the validity of 
some of their results, the non-dissociative character of the expansion of 
the permanent gases at high lemperatures, that all high temperature 
thermal measurement depends. 
Vapor tension. — Pyrometers of this kind have received little attention. 
Sajotschewsky 3 pointed out that the vapor tensions of different quanti- 
ties of liquid are identical as far as the absolute boiling point, after 
which the curves diverge. He further studied the temperature and 
pressure relation of twelve liquids in detail, at least as far as the critical 
point. The importance of vapor tension thermometers was signalized 
by Sir William Thomson, 4 but the remarks refer principally to low 
temperatures. Shaw 5 has recently inquired somewhat rigorously into 
such pressure-temperature relations. For moderately high temperatures 
Crafts's 6 paper seems to be the only companion research to Sajots- 
chewsky's. Crafts studied the boiling poiut and vapor tensions of 
mercury, and sulphur vapors, as well as of some carbon compounds 
with his hydrogen gas thermometer. 
Dissociation. — The difficulty in the way of a successful application of 
vapor tension thermometers, Lamy believed to have been overcome in 
his dissociation thermometer. In the suppositive case of marble, for 
instance, originally placed in a vacuum, the pressure due to the evo- 
lution of carbonic dioxide will increase with temperature, and would 
finally revert to the pressure zero when the original temperature is 
again reached. Debray's 7 data for the dissociation of calcic carbonate 
and Isambert's 8 further researches on the gaseous dissociation of solids, 
suggest a number of materials. Lamy 9 incloses these in an exhausted 
^lensching u. Meyer: Berl. Ber., vol. 19, 1886. p. 3295. 
2 Meuscliiiig u. Meyer: Gott. Nachr., 1887, p. 258. 
3 Sajotschewsky : Beiblatter, vol. 3, 1879, p. 741. 
4 Thomson: Proc. Royal Soc., Edinburgh, vol. 10, 1880, p. 532. 
5 Shaw: Trans. Cambridge Phil. Soc, Eng., vol. 14, 1885, p. 30. 
6 Crafts: Nature, vol. 26, 1882, p. 466. 
7 Debray: C.R.,vol. 64, 1867, p. 603. 
8 Isambert: These pr6sente a la Faculty des sciences de Paris, 1868. 
9 Lamy : C. R., vol. 69, 1869, p. 347 ; vol. 70, 1870, p. 393. Dingler's Jour., vol. 194, 
1869, p. 209 ; vol. 195, 1870, p. 525. 
(G92) 
