Send for 'em -- they're free; Free Things for Teachers, by Susan Osborn. New York: G.P. Putnam's Sons. $4.95.

Of course, before you can take advantage of the free things told about in this paperback, you've got to spend $4.95 to find out about them.

But it looks worthwhile.

The descriptions are clear, and the process for getting the materials is conscientiously presented.

And a few items do require a dollar or two.

But mostly, what's available free are what public-information departments of trade associations and businesses want to get out to the public.

More often than not, the only expenditure is a postcard.