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plate. A weak photographic effect was obtained. This was shown to be due to a penetrating radiation capable of passing through sheets of matter opaque to ordinary light. Further investigation showed that this photographic See also:

ACTION

action was exhibited by all compounds of uranium and by the See also:

metal itself, and had nothing to do with phosphorescence. It was shown equally if the uranium were kept in darkness and did not vary appreciably with See also:

time.

Becquerel showed that the rays from uranium like X rays were capable of discharging a See also:

BODY

body whether positively or negatively electrified. A uranium compound brought See also:

close to the charged plate of a See also:

gold See also:

LEAF (O. Eng. leaf, cf. Dutch loof, Ger. Laub, Swed. lof, &c.; possibly to be referred to the root seen in Gr. Ma-eta, to peel, strip)

leaf See also:

ELECTROSCOPE

electroscope causes a rapid collapse of the gold leaves. This property of uranium, and also of the radioactive bodies in See also:

general, has supplied a delicate and quantitative method of accurate comparison of the intensity of the radiations from substances under varying conditions. A modified See also:

FORM (Lat. forma)

form of gold leaf electroscope has come into general use for comparison of the radioactivity of substances. See also:

Rutherford (2) made a systematic examination of the discharging effect produced by the rays from uranium and showed that it was due to the production of charged See also:

CARRIERS

carriers or ions in the See also:

VOLUME

volume of the See also:

gas through which the radiations pass. In an electric See also:

field, the See also:

POSITIVE (or PORTABLE) ORGAN

positive ions travel to the negative electrode and See also:

VICE

vice versa, thus causing a See also:

DISCHARGE (adapted from the O. Fr. discharge, modern decharge, from a med. Lat. discargare, to unload, dis- and earn care, to load, cf. " charge ")

discharge of the electrified body. If a sufficiently strong field is used, the ions are all swept to the electrodes before appreciable loss of their number can occur by recombination. The See also:

RATE

rate of discharge then reaches a steady maximum value which is not altered by a large increase in voltage. This maximum current through the gas is called the saturation current. The ions produced in gases by the rays from uranium and other radioactive substances are in general identical with those produced by X rays, and the mechanism of conductivity of the gas is very similar in both cases (see See also:

CONDUCTION, ELECTRIC

CONDUCTION, ELECTRIC: § Through Gases). Some time after Becquerel's discovery, Mme See also:

CURIE, PIERRE (1859-1906)

Curie (3) made a systematic examination of the electric method of a large number of chemical elements and their compounds to test whether they possessed the " radioactive " property of uranium. Only one other See also:

ELEMENT (Lat. elementum)

element, thorium, was found to show this effect to a degree comparable with that of uranium—a result independently observed by See also:

Schmidt.

Mme Curie examined the activity of the various compounds of uranium and found that their radioactivity was an atomic property, i.e. the activity was proportional to the amount of the element uranium See also:

PRESENT

present, and was See also:

INDEPENDENT

independent of its See also:

COMBINATION (Lat. combinare, to combine)

combination with other sub-stances. In testing the activity of the minerals containing uranium, Mme Curie found that the activity was always four to five times as See also:

GREAT

great as that to be expected from their contentof uranium. If the radioactivity were an atomic phenomenon, this could only be explained by the presence in these minerals of another substance more active than uranium itself. Relying on this See also:

HYPOTHESIS (from Gr. inrorcOivat, to put under; cf. Lat. suppositio, from sub-ponere)

hypothesis, Mme Curie made a chemical examination of uranium minerals in See also:

order to try to See also:

SEPARATE

separate this new radio-active substance. In these experiments, the See also:

AUSTRIAN

Austrian See also:

Government generously provided Mme Curie with a ton of the residues from the See also:

State manufactory of uranium at Joachimstahl, Bohemia. At that See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place "there are extensive deposits of See also:

PITCHBLENDE, or URANINITE

pitchblende or uranite which are See also:

MINED

mined for the uranium. After separation of the latter, the residues are three to five times as radioactive weight for weight as the uranium. From this See also:

RESIDUE (through the French, from the Lat. residuum, a remainder, from residere, to remain)

residue Mme Curie separated a substance far more radio-active than uranium, which she called polonium in See also:

HONOUR (Lat. honos or lwnor, honoris; in English the word was spelled with or without the u indifferently until the 17th century, but during the 18th century it became fashion-able to spell the word " honor "; Johnson's and Webster's Dictionaries stereoty

honour of the See also:

COUNTRY (from the Mid. Eng. contre or contrie, and O. Fr. cuntree; Late Lat. contrata, showing the derivation from contra, opposite, over against, thus the tract of land which fronts the sight, cf. Ger. Gegend, neighbourhood)

country of her See also:

BIRTH (a word common in various forms to Teutonic languages from the root of the verb " to bear ")

birth. This substance is usually separated with See also:

BISMUTH

bismuth in the See also:

MINERAL

mineral, but by special methods can be partly separated from it. A further examination revealed the presence of a second radioactive substance which is normally separated with the See also:

BARIUM (symbol Ba, atomic weight 137'37 [0=16])

barium, to which the name " radium was given. This name was happily chosen, for in the pure state radium bromide has a very great activity—about two million times as great as an equal weight of uranium. By means of successive fractionations of the chloride, the radium was gradually concentrated, until finally the radium was obtained so that the barium lines showed very faintly.

The atomic weight was found by Mme Curie to be 225. In a See also:

RECENT

recent redetermination, using a larger quantity of o•4 grams of pure radium chloride, Mme Curie (4) found the atomic weight to be 226.2. See also:

Thorpe (5) using a smaller quantity obtained a value 227. The spectrum of the purified See also:

SAMPLE (through the O. Fr. essemple, from Lat. exemplum; a doublet of " example ")

sample of radium chloride obtained by Mme Curie was first examined by Demarcay. It was found to have a characteristic spark spectrum of See also:

bright lines analogous in many respects to the spectra of the alkaline earths. Giese! (6) found that pure radium bromide gives a brilliant See also:

CARMINE

carmine See also:

COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

colour to the See also:

bunsen See also:

FLAME (Lat. flamma; the root flag- appears in flagrare, to burn, blaze, and Gr. d, XEryew)

flame. The flame spectrum shows two broad bright bands in the See also:

orange-red. There is also a See also:

LINE

line in the See also:

BLUE (common in different forms to most European languages)

blue-See also:

green and two weak lines in the See also:

VIOLET

violet. Giesel (q) has taken an active See also:

PART

part in the preparation of pure radium compounds, and was the first to place preparations of pure radium bromide on the See also:

MARKET (Lat. mercatus, trade or place of trade)

market. He found that the separation of radium from the barium mixed with it proceeded much more rapidly if the crystallizations were carried out using the bromide instead of the chloride. He states that six to eight crystallizations are sufficient for an almost See also:

COMPLETE

complete separation.

From the chemical point of view radium possesses all the characteristic properties of a new element. It has a definite atomic weight, a well-marked and characteristic spectrum, and distinct chemical properties. Its See also:

COMPARATIVE

comparative ease of separation and great activity has attracted much See also:

ATTENTION (from Lat. ad-tendo, await, expect; the condition of being " stretched " or " tense ")

attention to this substance, although we shall see that very similar radioactive properties are possessed by a large mber of distinct substances. Radium emits three distinct types of radiation, known as the a, ,3 and y rays, of which an See also:

account will be given later. It produces in addition a radioactive See also:

EMANATION (Lat. emanatio, from e-, out, manare, to flow)

emanation or gas which is about See also:

ioo,000 times as active weight for weight as radium itself. The emanation released from to milligrams of pure radium bromide causes a glass tube into which it is introduced to phosphoresce brightly. A brilliant luminosity is produced in phosphorescent substances like See also:

ZINC

zinc sulphide, See also:

WILLEMITE

willemite and barium platino-See also:

CYANIDE

cyanide when introduced into a tube containing the emanation. The radium emanation, a more detailed account of which will be given later, has proved of the greatest utility in radioactive experiments. The property of radium of producing the emanation has been utilized as a very delicate and certain method, not only of detection but of estimation of small quantities of radium. This " emanation method " depends upon the introduction of the emanation, liberated from a sub-stance by boiling or See also:

HEATING

heating, into a suitable electroscope. The rate of discharge of the electroscope due to the emanation affords a quantitative measure of the amount of radium present. In this way, it is not difficult to determine with certainty the "ppg 4 ,, See also:

RAM I See also:

ION I, .

~ 8 11 0 2.

End of Article: RADIOACTIVITY

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