POPULAR MECHANICS 51
is to open the little window of your dark room and expose the frame about a second in the subdued daylight. Remove the plate carefully and develop in the usual way. There will be a negative of the picture you had at first; if you have been successful, if not. you should try it a time or two, varying the time of exposure.
In this manner you can make many pretty blue prints for your wall, or supply yourself with postal pictures of things impossible for you to take a picture of yourself. Should you have trouble with your high lights, print rather dark and bleach in following solution: Water. 100 ec Potassium Ferrlevanide (1/10 soL), 3 cc. Hypo <1 10 soL), 20 cc.
Wireless Telegraph
The accompanying diagrams show a wireless telegraph system that I have used successfully for signaling a distance of 3,000 ft. The transmitter consists of an induction coil, about the size used for automobiles, a key or push button for completing the circuit and five dry batteries. The small single point switch is left open as shown when sending a message, but when receiving it should be closed in order that the electric waves from the antenna may pass through the coherer. The coherer in this case is simply two electric light carbons sharpened to a wedge at one end with a needle connecting the two, as shown. An ordi- nary telephone receiver is connected in series with the coherer, as shown. To receive messages hold the receiver to the ear and close the switch and answer by opening the switch and operating the key. Contributed by Coulson Glide, 816 N. Temple Ave., Indianapolis, Ind.
— Constant Pressure Hydrogen Generator
By fitting three bottles.. A. B. C with rubber stoppers and connecting with.
glass tubes as shown in the sketch, hydrogen or other gases produced in a similar manner may be generated under constant
making! pressure. In hydrogen, bottle B is partzinc nodules filled with ly
a
formed by slowly pouring
melted zinc into water.
Hydrochloric acid is then
poured in the small fun-
thus partly filling
A and C. When acid rising from C comes in contact with the zinc, hydrogen gas is generated and fills bottle B. The gas continues to generate until the pressure is
nel,
bottles
A
the
bottle C, ceases.
when the
As
fast
-
acti
the gas
the pressure
depending on '."-- :z :lie
-~:_z
- ±
- :t::t tT
_i
A
Wireless Telegraph
- ie
and bottle B. A acid in bottle device is easily upset, a ring stand should be used to prevent its being broken, or if it is to be a permanent apparatus it- may be mounted on a
This apsubstantial wooden base. paratus may also be used for preparing acetylene gas or almost any gas which requires a mixture of a solid and liquid in its preparation. Contributed by C. S. J., Detroit, Mich.
—
for
nsed the
and generates
constant,
Wiring Diagram
is
acid rises in the tube
