4 
ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 161 
game conditions. The existence of the agent in a suitable and 
permanent colloidal state is, therefore, essential. 
In a general sense, sols may be stabilised by preparing them in the 
presence of an emulsoid, such as gelatin, which appears to surround 
the particles of sol and renders them less sensitive to salt solutions. 
Such protected sols may be evaporated to dryness and the residue— 
which is usually in the form of dark scales—can be brought back into 
a state of colloidal sols by the addition of water. Jf such “dried 
hydrosols” have been prepared from exceptionally pure materials- 
and with unusual care and skill, they form, when dropped into 
water, colloidal solutions in which the sol has the same properties as 
those previous to evaporation. The present writer has found, how- 
ever, that the commercial “dried hydrosols”’ which he has examined 
(which are sold under a variety of fancy names) have seldom been pre- 
pared with sufficient skill, and therefore do not yield “solutions” of 
the same power and therapeutic value as can be obtained without 
evaporation ; the advantage of portability gained by the production 
of the dried product is more than counterbalanced by the uncertainty 
as to the strength and activity of the sols produced by adding tap 
water to them in vessels which have not been specially prepared for 
the purpose, and by their instability in the presence of salts. For 
these reasons, he does not favour the use of the dried preparations, . 
except in cases where it is impossible to use those which have not 
been dried. Moreover, the stability of colloidal sols depends more 
on the mode of preparation than on the presence of a stabilising 
agent. Hence, excellent therapeutic results have been obtained with 
some colloids to which no protective has been added. 
It was realised about ten years ago that colloidal sols of certain 
metals inhibit the growth of all known bacteria, and it has since 
been found that they are harmless to the tissues. For this reason 
the use of colloidal sols has an enormous field of usefulness. They 
can be administered orally or injected in any desired quantities 
without any risk of toxication or undue shock to the system. 
The normal effects of colloidal sols on the blood stream is shown 
by the following experiment® :— 
“ A rabbit, weighing 1 kilo., was injected with 2 ¢.c. of collosol 
hydrargyrum in the auricular vein on the 14th of the month; on the 
16th of the same month 3c.c. more were injected. There was no 
local reaction, no bad symptoms ; the rabbit did not go off its food. 
On the 16th it was killed by the usual method, viz., chloroform. 
The arterial system of head and neck were perfused with normal 
saline solution (the eyeballs were very tense). The cerebro-spinal 
fluid was extracted under somewhat increased pressure. A post- 
mortem examination of the rabbit showed no change. A sample of 
the urine was taken, and also a slice of the cerebral cortex, which was 
- emulsified and allowed to settle. 
“These three fluids were examined under the ultra-microscope, 
and the observations made were as follows :— 
“The cerebro-spinal fluid showed a distinct cone, with many 
colloidal particles having a strong Brownian movement. 
* H. Crookes, “Recent Work on Metallic Colloids,” Journal of Chemical Technology, 
July, 1915, 
20895 F 
