g to renew my Leclanche batteries, which were
giving out, I bought some new empty porous cells. Please give the
following information: 1. Can I use the carbon plates of the old
elements over again? If so, do they need to undergo any washing or
soaking; or are they as good as ever? A. Yes. Soak them for a few hours
in warm water. 2. Is there anything I must add to the granular manganese
with which I fill the cells, in order to obtain maximum power and
endurance? Some makers add pulverized or even coarsely broken carbon. Is
it an advantage? A. It is an advantage to add granulated carbon to the
manganese. Use equal parts of each. 3. What is the exact composition of
the curdy mass which forms around and especially underneath the zincs of
newly mounted and old gravity batteries. Is this substance formed
naturally, or is it the result of using poor zinc or sulphate of copper?
A. It is copper, and should be removed, for it weakens the battery. It
is the result of placing the zinc in the sulphate of copper solution. 4.
Is there any real advantage in amalgamating the zincs of the above
batteries? A. No. 5. Is there a speedy way of cleaning them when coated
with this substance? A. They can be cleaned by scraping. 6. At certain
occasions my electric bells began ringing without anybody apparently
closing the circuit. I often notice that if I unjoin the batteries and
let them remain thus for a few hours, on reconnecting them the bells
would work all right for a week, sometimes a fortnight, when the same
trouble would again occur. Can you in any way explain this phenomenon?
The batteries are not placed in a very dry part of the house, but the
wires, which run pretty closely together, are nearly all exposed, so
that I can control the slightest corrosion or uncovering of the
conductors. A. There must be some accidental closing of the circuit. We
could not explain the action of your line without seeing it.

(14) J. E. E. asks: What is the number of layers of wire, and the size
used for the primary of the induction coil in the Blake transmitter, and
as near as you can the amount used for secondary? A. For primary, use
three layers of No. 20 magnet wire, and for the secondary use twelve or
fourteen layers of No. 36 silk covered copper wire. The resistance of
the secondary wire should be from 100 to 150 ohms.

(15) J. M. I. asks how to make a barometer by coloring ribbon, so that
they will change color, indicating weather changes. A. Use a