There are three general properties of the rays from radioactive substances which can be utilized for the purpose of detection:

(1) The action of the rays on a photographic plate.

(2) The phosphorescence excited in certain crystalline substances.

(3) The ionization produced by the rays in a gas.

The latter method, which is by far the most sensitive one, has been utilized in the Radium Detector.

Radium and other radioactive substances ionize by means of their intense radiation the surrounding air, which then becomes a conductor for electricity. An electrostatically charged body will therefore loose its charge when surrounded by ionized air. On this fact the design of the Radium Detector is based.

The Detector consists of the following parts:

Two stands (A) to each of which is fastened a little flag (B) and the generator (C).

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## How to Use the Radium Detector.

Place the two stands upon a table or a place where they stand straight and convenient for observation about six inches apart from each other. Then take generator (C) and rub the same briskly (without using much pressure) against your coat or a piece of silk or better pull the same through between a folded piece of dry cloth or silk, taking care not to touch the generator at the place where rubbing with your fingers. Then bring the generator close under the stand in a position as shown in the cut. It is not necessary to touch the stand with the generator.

The little flag (B) will now have raised and stand out horizontally. Touch the metal of the stand with your finger and the flag will fall down again. Then take your finger slowly away and then also the generator. After which the flag will raise and remain in this position.

See that you take your finger away first before removing the generator, otherwise the flag will not rise.

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Place now the substance which you
desire to test under or near to the
metal part (without touching it), of one
of the Detectors, and have the other
one, without the substance, placed at
least six inches away from the first;
then observe the little flags for about
six minutes.

If the flag of the Detector, near
which the substance is placed drops
down faster than the other one the sub-
stance is radioactive.

To make sure, however, it is neces-
sary to charge both Detectors again
and to place the substance now near
the other Detector for a second observa-
tion. To protect the flag from drafts, it
is advisable to cover the detectors with
inverted large glass tumblers, through
which the flags can be seen, but since
the Detector can be observed better
without being covered with a glass it is
best to work in a place where a draft
can be avoided.

Special care must be taken to keep
the apparatus dry, otherwise the electro-
static charge of the Detector will leak

away too fast and observations become
difficult.

If the generator is slightly damp and
also the cloth with which it is rubbed,
it is difficult to charge the Detector. In
this case it becomes necessary to dry
the same thoroughly.

The time for the flag to fall down
depends on the amount of radioactivity
of a substance placed in its neighbor-
hood.

The maximum distance through which
a radioactive substance will best effect
the Detector is two and a half inches.

Weak substances, such as uranium
nitrate, will cause the flag to fall in
eight or ten minutes. Pitch blende and
carnotite will accomplish this in two to
three minutes.

Concentrated radium compounds,
which are several hundred of times
more radioactive than pitch blende, will
affect the flag instantaneously.

The effect can be imitated by a
lighted match brought near to the
charged Detector.

Madame Sklodowska Curie has ex-

amined radioactive ores and chemicals.
I give here a list of some, arranged in
accordance to their strength of activity.
The list starts with the more active sub-
stances and ends with the weaker ones:

Pitch blende from Johannegeorgen-
stadt.

Pitch blende from Joachimsthal.

Pitch blende from Pzibran.

Carnotite.

Charcotite.

Autunite.

Black oxide of uranium.

Metallic uranium.

Orangite.

Green oxide of uranium.

Pitch blende from Cornwallis.

Cleveite.

Various thorites.

Uranate of ammonium.

Oxysulphide of uranium.

Uranate of sodium.

Uranate of potassium.

Samarskite.

Sulphate of uranium.

Nitrate of uranium.

THE RADIUM DETECTOR.
(Patent Applied For.)

L. M. Karnaseh, P. O. Box 794,
San Francisco, Cal.

Radium is a metal having an atomic
weight of 223.3; it is of eminent value
owing to its remarkable properties and
to its scarcity.

One pound of it costs at present
about $55,000,000.00. This high price
is partly due to the difficulty of ex-
tracting the metal from the ore. More
radium-bearing ore would have been
located if it was not for the impossi-
bility of detecting the same without
the help of a properly designed instru-
ment.

The Radium Detector is a highly
sensitive scientific apparatus, con-
structed on the principal of an elec-
troscope, by means of which it is pos-
sible to distinguish radioactive sub-
stances from others.

Radium quantities even smaller than
the 100,000,000th part of one pound can
be detected with absolute certainty with
the Radium Detector.

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