EDITORIAL OBSERVATIONS. 
409 
hoop, and strain it tight by pushing over it the one-inch 
hoop. The paper must be pressed smoothly up round the 
outside of the larger hoop, and the bottom must be quite 
flat and even. There must be no small holes in the paper. 
To try this, put distilled water into the dialyser, to the depth 
of a quarter-inch, and place the dialyser on some white 
blotting-paper. If any wet or dark spots appear, they 
indicate the existence of small holes. To close such holes, 
apply to the under surface of the paper about the holes some 
liquid albumen, put on a small patch of parchment paper, 
and iron the patch with a hot smooth iron. This coagulates 
the albumen, fixes the patch, and closes the hole. 
The dialyser being prepared, the liquid to be operated 
upon is to be put into it, to the depth of not more than half 
an inch, and the dialyser is then to be floated on distilled 
water contained in a flat basin. The quantity of the water 
in the basin should be about five times as much as that put 
into the dialyser. The whole is then to be set aside for 
twenty-four hours. 
A dialyser of six inches diameter serves to operate upon 
seven or eight fluid ounces of liquid; one of eight inches 
diameter for twelve or fourteen fluid ounces; one of ten 
inches diameter for twenty fluid ounces; and one of twelve 
inches diameter for thirty fluid ounces. The wider the 
dialyser and the greater the quantity of distilled water 
used in the outer basin, the more rapid and effective is the 
diffusion. 
Professor Graham, in explanation of his method, divides 
substances into two classes— crystalloids , those which have 
a tendency to crystallize, and are of high diffusibilitv; and 
colloids, which are of low diffusibility, affect a vitreous struc¬ 
ture, and have little effect on the volatility of the solvent. 
Animal gelatine is the type of the colloids; the plasticity of 
which, and its cognate compounds, renders them peculiarly 
fitting for animal organization, and as media for liquid dif¬ 
fusion, whilst their identity is still retained. To give an 
illustration of the manner in which analysation is conducted 
by the “dialyser,” we may take the following:—A mixed 
solution, containing sugar and gum, was placed upon the 
