4 PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
chang’e in its rapidity, or in the result when nitrous oxide was placed above it. The 
carbonic acid found in the upper bottle, and which had diffused into it from the 
lower, was 0‘231 when the upper bottle contained water alone, and 0‘229 when it 
was water charged with three-fourths of its volume of nitrous oxide gas, — to 1 car- 
bonic acid remaining undiffused in the lower bottle in both cases. 
It appeared, then, that the liquid diffusion of carbonic acid was a slow process 
compared with its gaseous diffusion, quite as much as days are to minutes. 
That this diffusion of the liquid carbonic acid takes place with undiminished vigour 
into water already saturated with nitrous oxide, the substance of all others most re- 
sembling carbonic acid in solubility and the whole range of its physical qualities. 
The diffusion of the liquid carbonic acid appears no more repressed by the liquid 
nitrous oxide, than the diffusion of gaseous carbonic acid is by gaseous nitrous oxide. 
But the chief interest of these observations was the practical solution which they 
give to the question, whether, in conducting experiments on liquid diffusion, acci- 
dental causes of disturbance and intermixture of two liquids, communicating freely 
with eaeh other, can be avoided. It was made evident that little is to be feared from 
accidental dispersion when ordinary precautions are taken. 
An excess of density in the lower liquid of not more than To“oofh part is found 
adequate to prevent any considerable change of place of the latter, — from expansion 
by heat, accidental tremors and such disturbing causes, which must exist, — for days 
together. 
(2.) Another early inquiry was, how far is the diffusion of various salts governed 
or modified by the density of their solutions. 
Solutions of eight hydrated acids and salts were prepared, having the common den- 
sity of T200, and were set to diffuse into water in the following manner: — 
Eighteen or twenty six-ounce phials were made use of to contain the solutions, and 
to form what I shall call the Solution phials or cells. They were of the same make 
and selected from a large stock, of the common aperture of 1T75 inch. Both the 
mouths and bottoms of these phials were ground flat. The mode of making an ex- 
periment was first to fill the phial to the base of the neck, or rather to a constant 
distance of 0'6 inch below the ground surface of the lip, A little disc of cork, pro- 
vided with a slight upright peg of wood, was then floated upon the solution in the 
neck, after having been first dipt in water. The neck itself was now filled up with 
pure water by means of a pointed sponge, the drop suspended from the sponge being 
made to touch the peg of the float, and water caused to flow in the gentlest manner, 
by slightly pressing the sponge. The only other part of the apparatus, the Water-jar, 
was a plain cylindrical glass jar, of which the inner surface of the bottom was flat or 
slightly concave, to give a firm support to the phial. The phial, with its solution 
only, was first placed in this jar partly filled with distilled water, and the neck of the 
former was then filled up with distilled water in this position, as before described, to 
avoid any subsequent movement. The phial was ultimately entirely covered to the 
