334 C. Barus — Status of. High Temperature Research. 



Having found the constants of equation (2), the values of 

 the second term of (1), 



io p/ + Q '*' 

 which now merely expresses the shortcomings of (2), may be 

 found by the same process. But in this case inspection will 

 usually suffice. 



From this point it would then be desirable to proceed in 

 such a way as to give the two terms of equation (1) (second 

 member) individual importance in their relation to the two 

 metals of the couple ; but as my present purposes are suffi- 

 ciently met by the above constants I will not enter further into 

 the work of finding characteristic parameters for each metal. 



4. Observations. — To test the equations given I have made 

 use of direct comparisons of the 20$ iridioplatinum thermo- 

 couple and the porcelain air thermometer published in my 

 Report on high temperature measurement,* and referring to an 

 interval of temperature between about 350° add 1100°. Virtu- 

 ally the calibration is made determinate by observations of the 

 boiling point of zincf taken at 930° ; for although the air 

 thermometer is based wholly on independent volume measure- 

 ments, and although the boiling points of both mercury and 

 sulphur are well reproduced in the lower part of the curve, I 

 do not derive much assurance from this without having quite 

 eliminated the stem error in a way which I hope soon to 

 describe. 



A second series of measurements, made more recently, is 

 contained in the following table. Here the electromotive force 

 e 20 in microvolts, while the cold junction is kept at 20° C, is 

 given for a series of known melting and boiling points due to 

 Regnault (Hg' and S') to Deville and Troost, (Zn'), to Troost 

 (Se'), to Yiolle (Zn', Ag, Au, Cu, Pd, Pt) to LeChatelier (Al, 

 Zn inferred), to Carnelley and Williams (Cd', ]STi, Se' inferred). 

 Accents denote boiling points. References will be found in 

 the Bulletin cited. 



MELTING POIXTS. BOILIN'G POINTS. 



Substance. Temperature. e. 20 . Substance. Temperature. e 20 . 



Zinc 415° 4260 Mercury-- 357° 3466 



Aluminum- 625° 7090 Sulphur... 448° 4580 



Silver 954° 11960 < i • ( 665° HQKn 



Gold 1045° 13520 belenmm.-j 683 o ,850 



Copper 1054° 13585 n , . 760° ftnQt7 



xr- i i ,,. A o -inr-on Cadmium.- h ^. a 9037 



JNickel 14o0 19630 ( i ib 



Palladium-. 1500° 21430 Zinc...... 930° 11105 



Platinum .. 1775° 24470 R . fl \ 1100° 1QOQA <> 



Bismuth .. - -,-™o I8930r 

 ( loOO 



Water 100° 680 



* Barus: Bull. No. 54, U. S. Geolog. Survey, Washington, 1889, pp. 226-227. 

 f See § 6. 



