218 
ArticLe VIII. 
Experiments on the Expansive Force of Steam. By Professor 
Gustav Maenus*. 
[From Poggendorff’s dnnalen, No. 2. for 1844.] 
IN a former memoir} I have shown that the various gases have 
not, as was previously believed, the same, but different coef- 
ficients of expansion. It is therefore probable that the coefficient 
of expansion hitherto admitted for steam is likewise not correct, 
and it appeared to me of great interest to ascertain this accu- 
rately. For this purpose, however, it was requisite to know the 
pressure of steam at various temperatures, especially between 
0° cent. and 100°. On perusing the investigations which had 
been made on this subject, I became convinced that I could lay 
down none of them as bases for my experiments, not only because 
the statements of the various experimenters do not sufficiently 
agree with one another, but because the methods employed by 
them are far from being perfect; and moreover, because in none 
of the investigations which have been published on this subject 
are the original observations communicated. All of them, indeed, 
contain, at least the recent ones, only the expansive forces calcu- 
lated for the entire degree, which necessarily differ according to 
the formula employed for their calculation{. Since we are 
moreover ignorant how far the actual observations differ from 
the values found by interpolation, it is impossible to judge what 
degree of accuracy the existing statements possess. I therefore 
resolved to submit this subject to a new investigation. 
The methods which have hitherto been employed to measure 
* Translated from the German by W. Francis, Ph. D., F.L.S. 
+ Poggendorff’s Annalen, vol. lvii. p. 177. 
t The table contained at the end of the first volume of Biot’s Traité de Phy- 
sigue, on the expansive forces of steam between 0° and 100°, which is copied 
in nearly all the French Manuals on Natural Philosophy, is calculated accord- 
ing to Dalton’s statements. (Biot’s Traité, i. p. 272.) But these themselves 
are the result of a calculation, and in fact according to quite a different for- 
mula, and are only partially founded on direct measurements of the expansive 
forces in a barometer tube, and partially on the observation of the temperature 
of water boiling under the air-pump at different pressures. Moreover, Dalton 
has considerably modified these statements in the second edition of his ‘ System 
of Chemical Philosophy.’ 
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