82 
PROFESSOR W. RAMSAY AND DR. S. YOUNG- 
The formula which Regnault employed in his extensive research on vapour- 
pressures was suggested by Biot. It is 
logy> = a-{-hot?-{-eft. 
The concordance between the found and calculated pressures through a range of 
temperatures so great as from —20° to 180° shows how well this formula interprets 
the facts. The constants employed were calculated from the observations at 0°, 45°, 
90°, 135°, and 180°. The numbers directly read were, however, not taken; but small 
portions of the curve about these points were previously smoothed by means of the 
simpler formula 
log p = a+5 at 
The constants for the larger formula are 
a = 5-9834771, 
log b = 0-5240258, 
log c= 1-5733238, 
b and c are both negative. 
The greatest difference, calculated as temperature between the found and calculated 
results between —15° and 180°, is 0’2°; but above 180° the difference increases 
gradually, amounting to 0'8° at 193°; but, indeed, it is doubtful whether any formula 
can be expected to hold in the immediate neighbourhood of the critical point. 
The vapour-pressures of ether were measured between —20° and 120° by Regnault; 
though his results agree with ours at certain temperatures, yet there is, on the whole, 
considerable discrepancy; and, in our opinion, he himself furnishes the explanation. 
In only one case was the specimen of ether used by him purified from alcohol by 
repeated shaking with water; and this specimen appears to have been used only in 
determining the specific heat of the vapour. He points out that after standing much 
lower vapour-pressures were obtained than with freshly distilled ether; for instance, 
at 0° his calculated number is 184-39 mms. In the first series, in which the ether 
had been distilled from calcium chloride, the pressure at —0-08° was 1ST7 mms., 
corresponding to 182-5 mms. at 0°. In the third series the same ether had stood for 
a year, and was redistilled over lime before experiment. The vapour-pressure at 0° 
was 181-65 mms. The same quantity of ether was again allowed to stand in sealed 
flasks, and on redetermining the vapour-pressure after six months it had fallen to 
174-9 mms., and after three months more to 171 *93 mms. Regnault states that the 
chemical composition was unaltered, and that the alteration was of a physical nature ; 
but Lieben (‘ Deutsch. Chem. Gesell. Ber.’, Jahrg. 4, p. 758) states that pure ether, 
either alone, or in contact with potash, lime, or sodium, does not change on standing; 
but that the presence of water, fused sodium chloride, calcium chloride, or anhydrous 
log a = 1-99827459, 
log/3 = 1-99130336 ; 
