Silica Gel - A dry subject

G’day. I have seen comments on the use of silica gel for drying
purposes, such as in tool drawers and for rolling mills, etc, to stop
rusting of steel parts. Silica gel is indeed an excellent drying
agent, but it must be used with a little thought. Many items these
days come packed in boxes with a little porous paper packet and
containing granules of colourless silica gel. This is fine, but the
silica gel will not continue absorbing moisture for ever. After
exposure to the atmosphere for a day, it will have absorbed all the
moisture it can. It may be reused many times by simply heating it; a
microwave oven is ideal. But how are you to know if it is dry and
ready to use? It is possible to buy silica gel granules which contain
an indicator, which is a salt of the metal cobalt, such as chloride
or sulphate, and that turns the granules blue when dry, and pink when
damp. Indicator gel granules are not very expensive and are sold by
the pound, but I regret that I can’t tell you where to buy it in your
country; all you can do is enquire in your locality, although all
laboratory suppliers will stock it. Keep it when dry - and blue - in
an air tight jar; an Agee jar is ideal, and lay a piece of porous
paper (coffee filter?) over it. If you put a damp watch on the paper
with it’s back open, it will completely dry in a night. To re use,
simply place on a dinner plate, and put it in the microwave oven at
medium heat for about 20 minutes. If you put the granules in a
drawer, they will turn from blue to pink in a night, indicating that
they have absorbed all the moisture they can, so the drawer may no
longer be regarded as dry. However articles of steel placed in a
plastic bag or an airtight plastic box with silica gel and sealed,
will stay completely dry. Remember, silica gel will remove moisture
from the atmosphere - but not for much over 24 hours.

For those who are inquisitive, silica gel is made from a solution of
sodium silicate, containing the cobalt indicator. When acidified, the
gel is precipitated and it is this when dried and crushed which forms
the hard silica gel granules used for drying.

Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ

If you have in your area a store that deals in firearms and the
safes used for them, then that store will also have silica-gel in
blocks about the same size as the magnesia block used for soldering
on. These can be heated in an oven when they change color indicating
that the block has absorbed all of the moisture in can. Then the
blocks can be used over and over. I do imagine that silica has a
reusable no, but don’t know what it is. I keep on in my safe.


In the US, you should be able to find indicator silica gel at any of
the chemical supply houses, such as E.H Sargent, Fisher, VWR, etc.;
check with your local high school (or college) chemistry department
and they should be able to tell you the closest one, and lend you a
catalog so you can mail-order some.

in Utah’s colorful Dixie