TRANSACTIONS OF WAGNER 
A COMPARATIVE STUDY OF THE RADIOACTIVE MINERALS 
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For the radiographic studies "x-ray" sensitive plates were enclosed in 
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thick black paper envelopes, and covered by plates of brass 1 mm. thick, pierced 
by square openings 1 cm. on a side. For development the following solution 
was employed: 
Wa. . 1000 С.С. 
hn е A A A EUN 30 g. 
[ЖР ES LE e ia v Ue aru: A EA. A IO Y. 
POSI ШОШ eein YE D EN E E N А Dg 
After remaining in this for four minutes, the plates were washed and fixed in 
the usual manner. 
'The minerals were carefully examined for the presence of inclusions or of 
alteration products, and chips were broken from the purest portions of each 
specimen. These chips were reduced in. an agate mortar to powder passing a 
roo-mesh sieve, and one gram of the powder was used for each experiment. 
For test in the electroscope the samples were placed in shallow, circular, 
pasteboard trays 2.5 cm. in diameter, and spread out as evenly as possible. The 
instrument having been charged, the lower plate was withdrawn, and one of the 
trays placed upon it; it was then rapidly replaced, the door closed, and the time 
required for the leaflet to pass over a certain division observed. The tray was 
then removed, the air in the box blown out, and the process repeated with the 
other samples. Most of these observations were repeated four times, on different 
days, and the mean result used. 
The same samples were used in the radiographic tests, the material being 
spread evenly over the holes in the brass plates, allowed to remain twenty-four 
hours, and the sensitive plates then developed, the conditions being as far as 
possible the same throughout. “The images obtained were compared by the use 
' made by J. Decoudun, of Paris, as recom- 
of the so-called “lens-photometer? 
mended by Bardet. The plates were successively placed in the front of a wooden 
box, so arranged that the light from a small incandescent lamp inside the box was 
reflected through them, at an angle of 45 degrees, by a sheet of white paper. 
'The photometer, consisting of a small tube with revolving eyepiece, was held in 
contact with the glass surface, and the eyepiece turned until the image of its 
opening became obscured, when the relative intensity of the light penetrating 
the plate could be read off. These readings were also repeated from three to 
five times, and the mean values used. 
