HEAT OF EVAPORATION OF WATER. 281 
preliminary experiments), the grease on the cores of the glass taps was replaced by a 
trace of phosphoric acid, which appeared to answer admirably. Thus, the apparatus 
can be used without alteration for all volatile liquids which do not act on the metals, 
a possibility I kept steadily in view when designing it. 
Fig. 1. 
Four way tap ly 

[May 4, 1895.—At the meeting of the Physical Society on January 11, 1895, 
Professor Ramsay exhibited an apparatus by means of which the comparative latent 
heats of evaporation of different liquids could be determined. I had the pleasure of 
seeing the apparatus at work, and from that time I abandoned all idea of extending 
my own investigation to other liquids than water. The method adopted by Professor 
Ramsay is so perfect, and at the same time so simple, that I feel that it would be 
waste of time and energy to pursue my absolute determinations. I mention this 
because many of the precautions described in the preceding sections were adopted 
with the view of conducting experiments with various liquids, and (as I now discover) 
might have been dispensed with. 
Professor RaMsAY now informs me that, although certain practical difficulties in 
the working of his apparatus have not as yet been entirely overcome, he has already 
determined (approximately) the comparative latent heats of evaporation of a con- 
siderable number of volatile compounds, and that the results will shortly be 
published. 
I venture, however, to call attention to the fact that the very perfection of 
Professor RAMsAyY’s method increases the importance of an accurate knowledge of the 
absolute latent heat of evaporation of water. | 
MDCCCXCV.—A. 20 
