128 
THE YOUNG SCIENTIST. 
■Varnishing: Paperhang-ing-s.— Give two coats 
of size, 1 ib. of pale glue in 1 gallon of water, 
should be used for oak and dark color, and when 
•dry varnish with hard oak varnish. For varnish- 
ing marble, tiles, and other light papers, use 
gelatine size and white paper varnish.— JP'arm- 
ture Gazette. 
Loose Screws.— It is a common thing, when a 
screw or staple becomes loose, to draw it out, 
plug up the hole or holes with wood, and then 
reinsert it. But screws and staples so secured 
^soon come out again. It has been found that a 
much better way is to fill up the holes tightly 
with cork. Screws and iron so secured will re- 
main perfectly tight, just as long as when put 
into new wood.— F. S. 
Blackboards.— For imparting a uniform black 
surface to boards that are to be used as black- 
boards take of shellac six ounces and of alcohol 
a pint and a half; warm the alcohol and digest 
the shellac in it until the latter is dissolved; 
strain the liquid through a cloth, filter it, and 
then introduce about five ounces of a mixture of 
boneblack and emery powder combined in equal 
parts, stirring the whole together until the in- 
:gredients are thoroughly incorporated; the mix- 
ture should have the consistency of very thin 
syrup. Thin, if necessary, with more alcohol, 
and apply two coats, using a soft, smooth-edged 
brush. 
Metallic Designs on G-lass.— An ingenious 
method of obtaining mirror-like designs on 
glass has been devised by Leclerc. The glass 
liavingbeen silvered by the chemical process, is 
coated with a thin and uniform layer of sen- 
sitive bitumen, and this is exposed under a 
transparency, the next step being to wash away 
the unaltered bitumen with oil of turpentine, so 
as to leave the bituminous design on the sil- 
vered glass. The application of moderately 
strong nitric acid removes the silver, excepting 
where it has been protected by ilie bitumen, so 
that the metallic design shows like a mirror 
from the reverse side of the glass. The plate may 
foe backed by paint or any other suitable mate- 
rial. 
Black Oak.— To turn oak black, so as to cause 
it to resemble ebony, the wood should be im- 
mersed for forty-eight hours in a hot saturated 
solution of alum, and then brushed over several 
times with a logwood decoction, prepared as fol- 
lows: Boil one part of best logwood with ten 
parts of water; filter through linen, and evapor- 
ate at n, gentle heat until the volume is reduced 
one-hnlf. To every quart of this add from ten to 
fifteen drops of a saturated solution of iiuligo, 
completely neutral. After applying this dye to 
the wood, rub the latter with a saturated and 
filtered solution of verdigris in hot concentrated 
acetic acid, and repeat the operation until a black 
of the desired intensity is obtained. To imitate 
rosewood, a concentrated solution of hyperman- 
ganate of potassa is spread on the surface of the 
wood and allowed to act until the desired shade 
is obtained. Five minutes suffice ordinarily to 
give a deep color. A few trials will indicate the 
proper proportions. The hypermanganate of po- 
tassa is decomposed by the vegetable fibres with 
the precipitation of brown peroxide of man- 
ganese, which the influence of the potassa, at the 
same time set free, fixes in a durable manner on 
the fibres. When the action is terminated, the 
wood is carefully washed with water, dried, and 
then oiled and polished in the usual manner. 
The effect produced by this process on several 
woods is remarkable. On the cherry, especially, 
it gives a beautiful red color. 
In continuing this department, which has been found of 
so much value, we would remind our readers who wish for 
information on any of the arts and sciences, that they are 
cordially invited to make their wants known through this 
column, and those of them who can furnish accurate 
answers to questions asked are requested to send in replies. 
Doubtless many of our subscribers may know of methods, 
processes, or devices that may be better or more suitable for 
the particular c?se in question than anything generally 
known, and it is this reason that induces us to keep this de- 
partment open for a medium, where an interchange of ideas 
and practices may be made to the advantage ot all our 
readers. Correspondents will please send their full address 
when forwarding their communications — either questions or 
answers — not for publication, unless expressly so stated, but 
so that we may know where to find the writer if desirable. 
Communications should be sent in on or before the 'first of 
each month previous to publicationj to insure insertion in 
next issue. 
Answers. 
41. MoNOGEAMS, G. F. M.. A. B., and G. S.— We 
have received monograms of these initials from 
several sources. A number of them came too 
late for this issue, and others did not possess 
sufficient merit for publication. We are pleased 
to find so many young people take an interest in 
