THE YOUNG SCIENTIST. 
3 
adheres to the table. A bunch of keys is 
now laid in the middle of the paper, and 
the latter is raised up by two of its cor- 
ners. If at this moment some one pres- 
'ents his knuckle o the bunch of keys 
he will draw from it a brilliant spark. If 
the weather be very dry, and if the paper 
has been well heated several times, the 
spark may attain a length of over half an 
inch. A spark may also be obtained by 
rubbing a glass tube with a piece of silk 
and approaching the knuckles to it. The 
human body may also be electrically 
charged, so as to yield a spark, by rapid 
sliding over a carpet, and gas may be 
lighted by the spark so produced. But 
in order to show energetic effects, the 
charge must be accumulated and con- 
centrated. This is best done by means of 
the Leyden jar, and in our next article we 
will tell our readers how to make a very 
simple apparatus of this kind. 
Imitation Flowers Made with Liquid 
Films. 
APEETTY experiment has been recently 
described by the well-known Belgian 
physicist, M. Plateau. He bends fine iron 
wire as in the figure, so as to present the 
contour of a flower of any number of 
petals. The central ring to which the 
petals are attached is supported on a 
forking stem, which is stuck in a piece of 
wood. After oxidizing the wire slightly 
FEAME FOR LIQUID FILMS. 
with weak nitric acid, the flower is dipped 
in glycerine liquid, so as to receive films 
in the petals and the central part. It is 
then turned up, placed on a table near a 
-window, and covered with a bell jar. For 
a short time at first it appears colorless, 
but soon a striking play of colors com- 
mences. In the experiment described by 
M. Plateau, the flower continued showing 
modifications of color for ten hours, when 
dusk stopped observation. Next morning- 
several petals had burst, the liquid used 
having been of very inferior quality. M. 
Plateau recommends preparation of the 
liquid thus : Dissolve a fresh piece of 
Marseilles soap, cut up into small pieces, 
in forty parts by weight of hot distilled 
water. Filter after cooling, and mix 
thoroughly three volumes of the solution 
with two of Price's or any other pure and 
heavy glycerine. The solution should be 
left at rest till all air bubbles are gone. 
Blue Process of Copying Drawings. 
THIS process is so simple and involves 
so little trouble that it has been almost 
universally adopted by engineers and 
mechanical draughtsmen. The following 
are the details as given by Mr. P. Barnes, 
of Springfield, 111., before the American 
Institute of Mining Engineers : 
1. Provide a flat board as large as the 
tracing which is to be copied. 
2. Lay on this board two or three thick- 
nesses of common blanket, or its equiva- 
lent, to give a slightly yielding backing 
for the paper. 
3. Lay on the blanket the prepared 
paper, with the sensitive side uppermost. 
4. Lay on this paper the tracing, 
smoothing it out as perfectly as possible, 
so as to insure a perfect contact with the 
paper. 
5. Lay on the tracing a plate of clear 
glass, which should be heavy enough to 
press the tracing close down upon the 
paper. Ordinary plate glass of three- 
eighth inch thickness is quite suffleient. 
6. Expose the whole to a clear sunlight, 
by pushing it out on a shelf from an 
ordinary window, or in any other con- 
venient way, for six to ten minutes. If a 
clear skylight only can be had, the ex- 
posure must be continued for thirty or 
forty-five minutes, and under a cloudy 
sky, sixty to ninety minutes may be 
needed. 
7. Eemove the prepared paper and 
