420 Dr. H. Hcrwig on the Expansion 



From a comparison of the numbers in brackets in this Table 

 with the numbers standing above each (which correspond to a 

 series of observations) it is obvious that the behaviour of alcohol 

 vapour totally differs from that of the two other vapours studied. 



The values of — — , near saturation, are decidedly greater for the 



first degrees of further heating, in consequence of adhesion; for 

 the higher intervals of temperature they partially become consi- 

 derably smaller. We see further that even in the little pressures 

 between 132 and 149 rnillims., where in my earlier investiga- 

 tions*! found the vapour still entirely in the gaseous state, a 



high positive value of -~ is shown. The phenomena of ad- 

 hesion, therefore, here completely mask the behaviour of the 

 vapour. 



On this account, in our further discussion of the results ob- 

 tained, the alcohol numbers must be altogether neglected. 

 Where adhesion comes into play, there we have to do with va- 

 riable quantities of vapour, and therefore with ratios utterly im- 

 possible to calculate. 



This leads us to a remark upon the investigation of steam (in 

 the same direction) by Fairbairn and Tate. These experimen- 

 ters, when experimenting on the specific volumes of steam from 

 the lowest point of saturation upwards f, preferred small incre- 

 ments of heat (a few degrees Fahrenheit), and believed they had 

 found coefficients of expansion of considerable magnitude; but 

 in a subsequent memoir J they traced the relations more accu- 

 rately, since even to themselves the previous results did not ap- 

 pear sufficiently reliable. 



They thus arrived at this result — that, from the limit of satu- 

 ration, steam heated within a space of constant dimensions exhi- 

 bits for the first two degrees a considerably higher coefficient of 

 expansion than air, while from that point upwards the coefficient 

 is the same for steam and for air. Translated into my formula 

 of calculation, this would signify that increases considerably 

 with the temperature for the first degrees, and then becomes 

 constant. I will leave out of consideration the fact that the 

 second part of this proposition is not strictly the expression of 

 their observations, and merely point out, with respect to the first 

 part, that in their experiments the initial pressures of the steam 

 amounted to less than half an atmosphere. This corresponds to 

 initial temperatures of at most a few more than 70 degrees 

 Celsius; and at such temperatures, according to my earlier ex- 



* Pogg. Ann. vol. exxxvii, p. 28. + Phil. Trans. 1860, p. 185. 



X Phil. Trans. 1862, p. 691. 



