374 Holborn and Day — Expansion of Certain 



Art. XXXII. — On the Expansion of Certain Metals at High 

 Temperatures; by Ludwig Holborn and Arthur L. 

 Day. 



[Communication from the Physikalisch-Technische Reichsanstalt, Charlottenburgf 



Germany.] 



The expansion of bodies at high temperatures has been so 

 little studied that the records are few and only indifferently 

 accurate. We therefore devised a new method and applied it 

 to the determination of the expansion of platin-iridium and of 

 porcelain up to 1000° for use in our recent measurements with 

 the gas thermometer and extended it afterward to various other 

 metals. Platinum, palladium and nickel were investigated up 

 to the same temperature, silver to near its melting point, con- 

 stantan to 500° and finally a single sort each of iron and steel 

 to 750°, these being of especial interest not only on account of 

 their special magnetic properties, but on account of their wide 

 technical application. 



On account of the difficulty in heating considerable lengths of 

 a metal uniformly, observations have usually been made hereto- 

 fore upon short pieces with necessarily diminished accuracy, or 

 the attempt at uniform heating has been entirely abandoned and 

 the bar allowed to project out of the oven at both ends, these 

 cold ends being provided with the marks upon which the 

 expansion observations are made. In the latter case the mean 

 temperature of the bar is determined with the gas thermometer 

 or by an electrical resistance method. 



This method has the disadvantage that the variation of the 

 expansion with the temperature cannot be properly observed. 



The arrangement of the apparatus in our experiments has 

 been already described.* A bar one-half meter in length, of 

 the metal to be investigated, is enclosed in an electrically heated 

 porcelain tube considerably longer than the bar. In this way 

 we obtained not only expansions of considerable magnitude (as 

 much as 9 mm in some cases), but also a very uniform tempera- 

 ture along the bar, the exact distribution of which was meas- 

 ured and not merely a mean value. 



Measurement of the Length.- — The expansion was measured 

 with the eye-piece micrometers of two fixed microscopes 

 arranged to observe certain marks near the ends of the bar. 

 The whole system was so solidly mounted upon a heavy stone 

 pillar that after several days' observing no displacement of the 

 microscopes could be observed equal in magnitude to the 

 errors of observation. The differences observed between the 



* Ludwig Holborn and Arthur L. Day, this Journal (IV), lvii, 17 1, 1900, also 

 Aimalen der Physik, ii, 505, 1900. 



