1] RADIO-ACTIVE SUBSTANCES id 
varied by blowing a current of air over the gas. In the course of 
an examination! of this action of the air current, the writer 
showed that thorium compounds gave out a material emanation 
made up of very small particles themselves radto-active. The 
emanation behaves like a radio-active gas; it diffuses rapidly 
through porous substances like paper, and is carried away by 
a current of air. The evidence of the existence of the emanation, 
and its properties, is considered in detail later in chapter vit. In 
addition to giving out an emanation, thorium behaves like uranium 
in emitting three types of radiation, each of which is similar in 
properties to the corresponding radiation from uranium. 
11. Radio-active minerals. Mme Curie has examined 
the radio-activity of a large number of minerals containing 
uranium and thorium. The electrical method was used, and the 
current measured between two parallel plates 8 cms. in diameter 
and 3 cms. apart, when one plate was covered with a uniform 
layer of the active matter. The following numbers give the order 
of the saturation current obtained in amperes. 
a 
Pitchblende from Johanngeorgenstadt 8:3 x 105 
5 Joachimstahl Bie (0 eee 
ai Pzibran ae a Cron a. 
a Cornwall oe, 660 Gy i. 
Clevite 500 von 600 ooo ooo 14 ” 
Chalcolite ... Bes ae bie See 5D ks 
Autunite .,. ee ates Bae Bf PARTIED Fen 
Thorites ye. ee S66 from 0°3 to 14 a, 
Orangite ... sin 500 sie one DO) 
Monazite ... se as ae sie O:5—" 45, 
Xenotine ... ep qe nds es 0-03 ,, 
Aeschynite Lis me an ae OY 2 
Fergusonite ee ‘fai at aif OAR: 
Samarskite ie aoe roe ae Dats, 
Niobite ... ies see Sie Bee OB 
Carnotite ... ane aa ‘ids es Gia. 
Some activity is to be expected in these minerals, since they all 
contain either thorium or uranium or a mixture of both. An 
examination of the action of the uranium compounds with the 
1 Phil. Mag. Jan. 1900. 
