314 Royal Society :— 
There is a curious connexion which may be mentioned, in this 
substitution of chlorine for oxygen in aldehyde, between the formula 
of these bodies containing chlorine, and those of the isomeric modi- 
fications of aldehyde. 
«Experiments on some of the Various Circumstances influencing 
Cutaneous Absorption.” By Augustus Waller, M.D., F.R.S. 
«On Spontaneous Evaporation.” By Benjamin Guy Babington, 
M.D., F.R.S. &c. 
The object of this communication is to make known certain powers 
of attraction and repulsion, hitherto, as far as I know, unnoticed, 
which are possessed by soluble substances in relation to their solvent, 
and which, in the case of ‘water (the solvent here considered), are 
measured by the amount of loss, on spontaneous evaporation, in the 
weight of solutions of different salts and other substances, as compared 
with the loss of weight in water. 
The force which holds together the particles of a vaporizable 
liquid is gradually overcome, if that liquid be exposed to air, by 
another force which separates, expands, and diffuses those particles 
in the form of vapour; and this separation takes place, even at a 
common temperature, so rapidly, provided the surface be sufficiently 
extensive, that an easy opportunity is afforded of determining the 
loss of weight by a common balance. 
A subject for investigation, possessing much interest, thus presents 
itself; and in its pursuit some new and unexpected results are 
encountered. 
The method which I have pursued has been to expose to the 
atmosphere, for a definite period, solutions of different salts, and also 
pure water under like conditions of quantity and area, temperature, 
atmospheric moisture, and atmospheric pressure. 
Different salts and other soluble substances are thus found to 
possess, when in solution, different powers of retarding or accelerating 
evaporation, and hence, from its amount, as compared with that which 
takes place in pure water, we can estimate the comparative value of 
those powers. 
The powers themselves being established as facts, the next point 
is to endeavour to discover the cause or causes on which they depend ; 
and a wide field of inquiry is thus opened. 
The following are the instruments which have been employed :-— 
1. A balance, for one of the scales of which is substituted a flat 
metal plate, six inches square, on which the vessels to be weighed 
can be conveniently supported. This balance will turn sensibly at a 
grain, even with a weight of 4 lbs. on either side. 
2. A number of copper pans tinned within, all of the same size, 
being precisely 5 inches square inside, with perpendicular sides 
3ths of an inch in height, also a number of earthenware pans of the 
same dimensions, The area of 25 square inches has been chosen, 
partly because this size is convenient for manipulation, and partly 
because the results obtained can be easily represented in decimals. 
This facility of decimal calculation would be of importance should 
such pans come into general use as hygrometers, for which purpose 
they are well adapted. 
