THE YOUNG SCIENTIST. 
149 
pathetic inks ordinarily used can be relied upon 
as a safe means for carrying on a secret cor- 
respondence, from the fact that none of them 
will bear exposure to a degree of heat just suf- 
ficient to scorch the paper. 
The term sympathetic ink is applied to any 
liquid which is used to write letters which re- 
main invisible until the writing has been ex- 
posed to heat, to some peculiar vapor, or to 
some suitable solution. Of those which are 
brought out by the use of a chemical liquid, 
the best is a weak solution of starch. This 
is invisible under ordinary circumstances, 
but becomes quite distinct when washed with 
a solution of iodine. Writing that is invisible 
until exposed to heat may be made with milk, 
lemon juice, onion juice, etc. 
In using a sympathetic or secret ink, it is 
always necessary to write some unimportant 
matter on the paper or postal card, and be- 
tween the lines write with the secret ink. If 
this method of correspondence were used for 
anything but an interesting experiment, how- 
ever, it would not be difficult to find a means 
by which, after writing with the secret ink, un- 
important matter might be written with com- 
mon ink directly over the first writing, and 
then, by means of a suitable fluid, the last 
writing might be washed away, and the first 
writing brought out. 
Imitation Ground Glass that Steam 
will not Destroy. 
Put a piece of putty in muslin, twist the 
fabric tight, and tie it into the shape of a pad; 
well clean the glass first, and then putty it all 
over. The putty will exude sufficiently through 
the muslin to render the stain opaque. Let it 
dry hard, and then varnish. If a pattern is 
required, cut it out in paper as a stencil; place 
it 80 as not tb slip, and proceed as above, re- 
moving the stencil when finished. If there 
should be any objection to the existence of the 
clear spaces, cover witli slightly opaque varnish. 
In this way very neat and cheap signs may be 
painted on glass doors. 
Glass Working. 
Glass is usually brought into shape by being 
moulded or blown. There are a few other op- 
erations, however, which are constantly needed 
by the amateur, and which we will describe. 
For cutting flat glass, such as window panes, 
and for cutting rounds or ovals out of flat 
glass, the diamond is the best tool; and, if the 
operator has no diamond it will always pay to 
carry the job to a glazier rather than waste 
time and make a poor job by other and inferior 
means. When, however, it is required to cut 
oflf a very little from a circle or oval, the dia- 
mond is not available, except in very skilful 
hands. In this case a pair of pliers softened 
by heating, or very dull scissors, is the best 
tool, and the cutting is best performed under 
water. A little practice will enable the oper- 
ator to shape a small round or oval with great 
rapidity, ease and precision. When bottles or 
flasks are to be cut, the diamond is still the 
best tool in skilful hands; but ordinary oper- 
ators will succeed best with pastilles, or a red 
hot poker with a pointed end. We prefer the 
latter, as being the most easily obtained and 
the most efficient; and we have never found 
any difficulty in cutting off broken flasks so as 
to make dishes, or to carry a cut spirally round 
a long bottle so to cut it into the form of a 
cork-screw. And, by the way, when so cut, 
glass exhibits considerable elasticity, and the 
spiral may be elongated like a riuglet. The 
process is very simple. The line of the cut 
should be marked by chalk, or by pasting a thin 
strip of paper alongside of it; then make a file 
mark to commence the cut; apply the hot iron 
and a crack will start; and this crack will follow 
the iron wherever we choose to lead it. In 
this way jars are easily made out of old bottles, 
and broken vessels of different kinds may be 
cut up into new forms. Flat glass may also be 
cut into the most intricate and elegant forms. 
The red hot iron is far superior to strings wet 
with turpentine, friction, etc. 
For drilling holes in glass, a common steel 
drill, well made and well tempered, is the best 
tool. The steel should be forged at a low tem- 
perature, so as to be sure not to burn it, and 
then tempered as hard as possible in a bath of 
salt water that has been well boiled. Such a 
drill will go through glass very rapidly if kept 
well moistened with turpentine in which some 
camphor has been dissolved. Dilute sulphuric 
acid is equally good, if not better. It is stated, 
that at Berlin, glass castings for pump barrels, 
etc., are drilled, planed and bored, like iron 
ones, and in the same lathes and machines, by 
the aid of sulphuric acid. A little practice with 
these different plans will enable the operator 
to cut and work glass as easily as brass or iron. 
Black diamonds are now so easily procured, 
