384 
POPULAR SCIENCE REVIEW. 
words by describing an experiment. If a sheet of very thin 
letter-paper, well sized with starch, and having no porosity, be 
laid on the surface of water, a depression made in its centre, 
and a mixed solution of cane sugar and gum arabic be poured 
upon it, the sugar diffuses through the water, while the gum 
remains above. The vegetable parchment or parchment paper 
of De la Rue is peculiarly adapted for experiments on dialysis. 
The passage of liquids through porous septa, which was .first 
studied by Dutrochet, was originally designated by the corre- 
lative terms endosmose and exosmose : in place of which Graham 
proposes the simpler term osmose (from cocr/xos, impulsion). 
Osmose has been supposed to be the unequal absorption of the 
two liquids placed on either side of it by the porous septum. 
Graham comes to the conclusion that osmose depends essentially 
on the chemical action of one of the liquids on the septum. 
The following passage, quoted from Graham’s Elements of 
Chewnstry , appears to embrace all the points necessary for our 
present consideration : — 
“ These experiments were made partly with porous mineral 
septa, partly with animal membrane. The earthenware osmo- 
meter consisted of the porous cylinders employed in voltaic 
batteries, about five inches in depth, surmounted by a glass tube 
06 inch in diameter, attached to the mouth of the cylinder by 
means of a cap of gutta percha. The cylinder was filled to the 
base of the glass tube with a saline solution, and immediately 
placed in a jar of distilled water ; and as the fluid within the 
instrument rose during the experiment, water was added to the 
jar to equalise the pressure. The rise (or fall) of the liquid 
in the tube was very regular, as observed from hour to hour, 
and the experiment was generally terminated in five hours. 
From experiments made on solutions of every variety of soluble 
substance, it appeared that the rise, or osmose, is quite insigni- 
ficant with neutral organic substances in general, such as sugar, 
alcohol, urea, tannin, &c. ; so likewise with neutral salts of the 
earths and ordinary metals, with the chlorides and nitrates 
of potassium and sodium, and with chloride of mercury. A 
more sensible but still very moderate osmose is exhibited by 
hydrochloric, nitric, acetic, sulphurous, citric* and tartaric acids. 
These are surpassed by the stronger mineral acids, such as sul- 
phuric and phosphoric, and by sulphate of potash, which are 
again exceeded by salts of potash and soda possessing a decided 
acid or alkaline reaction, such as binoxalate of potash, phosphate 
of soda, or the carbonates of potash and soda. The highly 
osmotic substances were also found to act with most advantage 
in small proportions, producing, in fact, the largest osmose in 
the proportion of one quarter per cent, dissolved. The same 
substances are likewise always chemically active bodies, and 
