Daily Kennebec journal. [microfilm reel] (Augusta, Me.) 1870-1975, 1912-04-23
cOLLOIDAL SOLUTIONS.

Sir J. ]. Thomson is giving a series
of lectures to members at the Royal
Institution, London. On March 16the
subject was .Colloidai Solutions 49,
A coIloid, Sir ]. j. Thomson ex-.
planned, is a sticky. Shiny substance,
capricious in it's behavior and at hrst
sight it does not appear to be- an In
teresting subject for Investigation
Gum, caramel, soap and white OF egg
are examples of colloids.
A coilodiai solution, however. exhiDitS
some very interesting properties. sucn
a solution seatters light, as can easily De
seen by placing solution OF soap ana
water In beam of light. This Is que TO
the fact that In colloidal solution the
particles are very small. and yet are
larger than molecules. These particles
are too small to be detected by an ordi~
nary microscope, but by means Of the
ultra microscope they can be seen. The
noteworthy point about the ultra micro
scope is that the only light which Is al
lowed in II Is the light scattered by the
particles The particles range In size
from to exl0-5 two to six multiplied by
10 to the minus five), and the ultra mi
croscope. is capable Of detecting particles
as small as 10 to the minus seven.
On the table during tile lecture stood
bottle of solution of colloidal gold.
prepared. the lecturer said. IS years ago.
The solution looked quite homogeneous.
/. e., no settling had occurred. The par
ticles are so small that 1t has been cal
culated that they would only fall about
one centimeter a year. and It is almost
impossible to prevent convection currents
which keep the solution sufficiently
stirred to prevent even this small fall.
but the influence of surface tension alone
would cause the particles to coagulate
and form solid lump. The reason that
this does not take place is that the par
tieles are electrified and consequently
the repulsion they exert on each other
resists the surface tension. By intro
ducing some electrolyte which Is DISCO
| ciated, the particles can be neutralized
| and will then ooagulate.
To show this the lecturer repeated an
experiment first made. he told us, nearly
| 60 years ago by Faraday. He added to a
little of the colloidal gold solution some
phosphorus dissolved In ether and then
some brine. Then he held the test tube
ilf beam of light and we saw the liquid
gr sdually become clear. This neutralIza-
tioIs accounts for mud settling at the
mouths of rivers. Some coloidal solu-
tons are negatively and some positively
ELECTRIFIED and If two solutions opposite
y electrified are mixed they neatralize
each other and precipitate Is formed
In preparing these colloidal solutions
| distilled water must be used. as tap
| water tends to make them coagulate. and
4 this is the reason that some water Is 80
unpleasant to wash in as 1t coagulates
| the soap.
/ In the case of negatively electrified So
| lutions the lecturer explained it is the
positive ions that are necessary to nett
fralize them. Thus, 1t Is irnmatsrtal
which salt of any particular metal Is
used. but different metals produce vary
| ing effects. Metals with high volency
are the most effective. trivalent metals
being a thousand times more effective
than divalent ones. In positive solutions.
on the other hand, the salt is the fmpor-
tarrt factor.
Concluding. the lecturer said that In
studying colloidal solutions where there
are such enormous surfaces. he thought
1t possible that not changes OF tempera-
ture merely. but rather surface tension
was the important factor.-Christisa
Science Monitor.