383 
“A MESSAGE FROM THE STABS.” 
The diffusion of liquids into each other is a remarkable 
expansion of the facts discovered with regard to gases. When 
two liquids of different densities, and capable of mixing, are 
placed in contact, diffusion takes place ; the rate of diffusion 
varying with the nature of the liquids, the temperature, and 
the degree of concentration of the solutions used. The manner 
in which the experiments are made is exceedingly simple. An 
open phial is filled with the solution to be experimented on, say 
the ammonia-sulphate of copper, and a light float placed upon its 
surface. This is placed in a confectioner’s glass jar, and water 
is steadily poured in so as to cover the open phial to the depth of 
about an inch. The saline fluid in the bottle is now in contact 
with the water in the jar, and diffusion proceeds. The ammonia 
leaves the copper, and the purple solution becomes of a pale 
blue colour, the volatile alkali being found diffused in the 
water. The amount of salt diffused, called the diffusate or 
diffusion product , is determined by chemical means. Such is 
the general mode of experiment, and such the character of the 
results. It is sufficient for the present purpose that the general 
law is stated. etf The velocity with which a soluble salt diffuses 
from a stronger into a weaker solution is proportioned to the 
difference of concentration between two contiguous strata.” * 
Graham has found that bodies may be divided into two 
classes in relation to diffusion. One class, which are the most 
diffusive, he terms crystalloids . Another class are non-crys- 
tallisable, as hydrated silicic acid, hydrated alumina, and 
metallic oxides of the aluminous class, when they exist in the 
soluble form. Animal and vegetable extractive, gelatin, starch, 
gum, &c. are of this order. Gelatin is regarded as the type of 
these, and from /coWy, glue , the term colloids is adopted. This 
peculiar form of aggregation is called the colloidal condition of 
matter , and we find it to be a state required in all the substances 
which can intervene in the processes of life. Space will not 
admit, on the present occasion, of that examination of this re- 
markable class of bodies which is desirable, since they play a 
highly important part in natural phenomena. The colloidal is 
regarded as a dynamical state of matter, while the crystalloid al 
is the statical condition. Colloids are ever in a state of muta- 
tion. Metastasis has been well said to be the condition of their 
existence. So remarkable are the phenomena of colloidal bodies, 
that those minds which have a materialistic tendency look upon 
them “ as the probable primary source of the force appearing in 
the phenomena of vitality.” 
These colloid substances are separated from other bodies by a 
process called dialysis. This will be explained in the fewest 
Phil. Trans. (1862), p. 1. Journ. Ckem. So?, xv. p. 217. 
