s agn 
L. H. Borgström. | SR (CIX 
DN 
There is no formula, which is able to render with precision 
the curve of temperature and pressure ranging from pressures 
measuring only a few millimeters up to pressures of ten or a 
hundred atmospheres. We have however a fair conceplion 
of the general appearance of this curve. The curves of most 
substances have a nearly similar course. This fact-was already 
in 1879 recognized by Dähring!), who adwanced the 
thesis, that the temperature-distance between the boiling 
points of a certain fluid at two given pressures is porportional 
to the temperature-distance between the the boiling points 
of another fluid at the same pressures: 
rg (1) 
Thus tf, and t, are the boiling points of two fluids under a 
certain pressure, t,' and tf," their boiling points under another 
pressure. Ramsay and Y oun g?) arrived 1886 through 
their comprehensive investigations of the relation between 
the boiling point and pressure to the expression: 
Tr 
T; T, 
FET (2) 
Thus T, and 7T; are the boiling points, on the absolute 
scale of temperature, of the two substances under a certain 
pressure and Ty,' and Ty the corresponding boiling points 
under another pressure. The second term on the right side 
may be regarded as a correction term as it is usually small 
compared to the difference T,'—T,. The substances, which 
follow D ähring's expression give in Ramsay's and 
Y oun g's formula the empirical constant c=0. In this case 
the latter formula may be written: = 
1 Däöhring. Neue Grundgesetze zur rationellen Physik u. Chemie. 
Leipzig 1878. Cit. Ostwald. Lehrbuch d. allg. Chemie. 2:o Ed. Leipzig 
1891. 
? Ramsay and Young. Phil. Mag. 21, 33 (1886). 
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