, etc., see p. 203, vol. 30.--W.C.L. will
find directions for preserving eggs on p. 306, vol. 34.--R.M.G. will
find a recipe for root beer on p. 138, vol. 31.--W.F.H.'s plan for a
refrigerator might answer. See p. 251, vol. 31.--J.C. can remove the
wool from pelts by steeping the skins in water, and hanging them up
till the wool putrifies. Then scrape with a blunt knife. For cleansing
wool, see p. 6, vol. 32.--W.H.J. will find a recipe for a cement for
marble on p. 344, vol. 32.--T.B. can gild his steel scabbard by
following the directions given on p. 106, vol. 34.--A.H.B., J.A.C.,
W.H.H., J.F.P., D.S., J.N.H., J.P., F.F., M.N., M.C., R.C., K.S.W.,
T.J., and others, who ask us to recommend books on industrial and
scientific subjects, should address the booksellers who advertise in
our columns, all of whom are trustworthy firms, for catalogues

(1) R.H.C. says: We have a slate roof which leaks very much. I have
not discovered any defect in the way in which it was put on; it
appears to be perfect. The pitch may be too low, and the rain may be
driven through by the wind on this account. Is there any wash, paint,
or cement that might be used for the purpose of remedying this defect?
A. There is an india rubber paint which is used to make leaky roofs
tight, but we have not learned of its being applied to slate roofs.

(2) C.C.B. says: I am making a small steam engine. The cylinder has,
inside diameter, about 1 inch with 21/2 inches stroke. What would be the
most suitable material and dimensions for the boiler? A. Make one 10
or 12 inches in diameter and 18 inches high, of 1/8 inch iron. You can
carry 60 lbs. steam pressure.

(3) M.C. says: I have had charge of some greenhouses that were erected
about four years ago; they are thoroughly heated, and all the pipes
have a thick coat of black paint. The houses never gave any
satisfaction, no matter how healthy the plants were in the fall. Soon
after the fires were lighted both leaves and flowers began to drop,
and some plants died. My predecessors attributed it to gas getting
into the houses. Upon inquiry I found no gas was there except when the
pipes were hot, and that the hotter they were the worse it was. In my
opinion, the cause of the trouble was a strong smell of paint from the
pipes. Since then I only keep heat enough to save the plants from
freezing. A. From your statement there is no doubt that the paint used
on the pipes was an imperfectly purified coal tar. Such tar