40 
THE YOUNG SCIENTIST. 
thicknesses of good brown paper, and *' choke" 
the end a little with a cord, so as to make a 
contracted place at the lower end. The object 
•of this is to prevent the plaster plug from 
falling out, which it would do if the paper tube 
were smooth. Tie the paper firmly with twine, 
both where choked, and also higher up. Allow 
at to project about half an inch beyond the 
wooden cylinder, and in the space thus left 
Fig. 3. 
pour plaster of Paris mixed with water, in the 
same way that lamp dealers use it for fixing 
chimneys on lamps. When the plaster has set 
and become hard, the porous cell is made. 
The zinc is simply a sheet cut to the proper 
size, and rolled into a cylinder. It may be 
amalgamated if the experimenter chooses, but 
works quite well without this. It must have 
a stout copper wire soldered* to it as shown in 
the figure. 
The solutions required are a saturated solu- 
tion of sulphate of copper (blue vitriol, a salt 
worth about 14 cents per pound), and a satur- 
*The process of soldering is so frequently neces- 
sary, and it is also so simple and easily performed, 
that we shall give minute directions for performing 
it in our next issue. 
ated solution of glauber's salts (sulphate of 
soda), to each pint of which two teaspoonsful 
of sulphuric acid (oil of vitriol) should be 
added. Arrange the various parts as shown in 
Fig. 4, where the battery is seen in section, 
the poles being connected by a fine iron wire 
which has just been fused. In this figure E is 
the outer can; D, the paper cylinder forming the 
Fjg, 4. 
porous eell; and C, the zinc cylinder. Join the 
wire attached to the zinc to that attached 
to the can. The surfaces of the wires should 
be made bright where they come in contact, 
and they may be held together by means of a 
spring clothes-pin. Then fill the porous cell 
to within half an inch of the top with the solu- 
tion of sulphate of soda, and fill the space be- 
tween the tin can and the porous cell with 
sulphate of copper. A current of electricity 
will at once be set in motion, and after a short 
t\me, say, fifteen minutes, the interior of the 
tin can will have been completely coated with 
copper. 
The reason for arranging the battery, and 
connecting the wires hefore pouring in the 
liquid is to give the can an opportunity to be- 
come coated by electro-deposition instead of by 
the chemical action of the sulphate of copper 
on the tin. The latter is apt to give a mere 
powdery coating, but the battery lays on a firm 
sheet of copper. 
One such cell is capable of charging weakly 
