14 
THE YOUNG SCIENTIST. 
top of the shield a mass of large ferns was fastened 
with a feathery dried grass, introduced here and 
there, which produced a very graceful pleasing eflfect. 
The climbing ferns were used for festooning the 
leafless branches. As a balancing point to the 
bird singing, I fastened a cocoon of the Attacus 
'CecropiO' with the moth above it, as though it had 
just come forth. A few brilliant insects stuck on 
here and there in the way of finishing touches, com- 
pleted this grouping of bits of Nature's odds and 
^nds. A. W. Eoherts. 
To Pour three DiflFerent Liquids out of one 
Vessel. 
Conjurers generally perform this feat by means 
-of a bottle divided into compartments, but the 
young chemist can easily do it with very little prepa- 
ration. Take three tumblers, and into one pour a 
very little (three or four drops) of a strong solution 
■of acetate of lead ; into another, a solution of sul- 
phate of copper, and into the third, a little tincture 
of iron. The quantities of these liquids may be so 
small that they will not be perceived by those to 
whom the trick is shown. Then provide a pitcher 
(preferably of glass, because it is transparent and 
■shows that there is no trickery about it), and fill it 
with water, in which an eighth of an ounce of prus- 
;siate of potassa has been dissolved. On filling the 
tumblers out of this pitcher, one will be filled with 
white liquid resembling milk ; a second with a blue 
liquid, and the third with a dark red liquid. To 
those who see it for the first time, this experiment is 
very striking. The explanation is simple. The 
prussiate of potash (potassic ferrocyanide), is de- 
composed in all three cases, and white, red and blue 
compounds formed with the lead, copper and iron 
respectively. 
To fire a Cannon with an Icicle. 
Load a small cannon very lightly with powder, 
and prime it well. On the priming lay a small piece 
of potassium. If the priming be now touched with 
an icicle or a moist stick, the potassium will take 
^re and fire ofi" the cannon. 
In handling potassium, be veiy careful not to touch 
It with moist fingers or anything damp, or it will cer- 
tainly take fire and produce very serious burns. 
Hold it with a pair of forceps or tweezers, (such as 
accompany every sewing machine), lay it on dry 
blotting paper, and cut off what you want. A piece 
the size of a grain of mustard seed is large enough. 
An Acoustic Experiment. 
Let a wide glass tube, open at both ends, be taken, 
and in thin apiece of fine wire gauze be pushed up 
some little distance. If the gauze be now heated to 
redness over an ordinary Bunsen burner, and then re- 
moved, it will shortly emit a shrill note, lasting from 
:five to ten seconds. The experiment will be new to 
most of our readers, and has the merit of always go- 
ing oflf. 
Drawing Boards for Amateurs and Students. 
The best kind of drawing board for amateurs 
and students, is made of good pine without cleats 
or cross-pieces. The end cross-pieces usually put 
on drawing-boards are very objectionable, on ac- 
count of the unequal shrinkage of the body of the 
board with the grain of the wood running longitu- 
dinally, and the grain of the cross-pieces which run 
tranversely, or at right angles with the former, 
always leaving shoulders or projections on the edges 
of the board, that prevent the accurate use of the T 
square. The most convenient size for a board is 27 
inches by 21. This takes half a sheet of double ele- 
phant drawing paper, which will be found the best 
size for ordinary work, the smaller sizes being too 
light for finished mechanical drawing. And it will 
be found that a board of this size, made out of clean, 
sound and well-seasoned pine, will stand without 
any cleats or cross-pieces. It should be left quite 
plain and neither oiled or varnished. 
The most important point is that the sides should 
be parallel, and that one of the ends at least should 
be at perfect right angles to the sides. This end 
should be marked and always placed at the left 
hand, and it is of very little consequence about the., 
other end. But it will be found that it is not such 
an easy matter to get the end and sides square as 
some people think. Ask the majority of carpenters 
to do it for you, and they will fail. You must either 
do it yourself, or watch and guide them while they 
do it. 
The best way is first to make one end perfectly 
straight. Never mind its relation to the sides ; get it 
perfectly straight, and when you have it so, never 
touch it afterwards, but keep it for a guide or base 
line. The end being straight, make one side square 
with it. To find out whether it is square or not, you 
must not rely upon common iron squares, but you 
must test it with your T drawing square. And by 
the way, it is of no consequence whether the blade of 
this square is square with the stock or not ; if the blade 
and stock are both straight, this is all that is neces- 
sary. For if yau think a little, you will see that the 
angles in your drawing depend upon the board and 
not on the square. To test the board therefore, apply 
your T square to the side you are working on, draw 
a line across the right-hand end within an inch of the 
edge. Then apply the square to the left end, and draw 
a line across the center of the board. Try, by the or- 
dinary rules of practical geometry, whether or not 
these lines are at right angles. If so your work is 
done ; if they vary a hairsbreadth, plane off a little 
from the side, and try and bring them true. 
Drawing paper should be mounted, for finished 
drawings (colored or shaded), but for common work 
it is more convenient to fasten it to the board with 
drawing pins or thumb tacks. Hence the necessity 
of having the board of soft wood ; if otherwise, the 
pins will be blunted, bent, and difficult to press in 
and draw from the board ; this operation can gen- 
erally be done by the thumb nail. 
