[EVE & M’INTOSH] RADIUM IN ROCKS NEAR MONTREAL 15 
the movement of the gold leaf was measured by a microscope with a 
graduated eye-piece. Since the emanation increases to half its maxi- 
mum value in about 3.8 days, it is easy to calculate the maximum 
from the amount measured after any definite period. It was found 
by experiment that the emanation was not lost to an appreciable extent 
by absorption when collected over water, if placed in the electroscope 
without delay. 
The electroscope, which is shown in the figure, consisted of a 
filter flask silvered within; strips of tin foil moistened with phosphoric 
acid connected the silver coating to the earth wire. The flask was 
closed by a rubber stopper to which the usual gold leaf arrangement 
was attached. It could be exhausted by a water pump to a pressure 
of 2 cms. of mercury. Air and emanation were admitted through 
a capillary tube and a bulb of phosphorus pentoxide. The natural 
leak of the electroscope was 3.9 divisions an hour, and this remained 
remarkably constant, provided the electroscope was exhausted and 
refilled daily. The electroscope was not influenced by exterior 
electrification, nor by atmospheric conditions. 
Blank tests were made involving all the chemicals and all apparatus 
used in the experiments. No radio-active matter could be detected by 
these tests. 
The electroscope was standardized by inserting the air and 
emanation boiled from a flask containing 1.57 10—® gram of radium, 
and the resulting effect was a movement of 10.3 scale-divisions per 
minute. 
The solutions were tested two or three times so as to ensure 
accuracy. The results obtained were as follows :— 



Grams of radium 



Period. Rocks in order of age of formation. per gram of rock 
Ordovician "7" Trenton Limestone ARE AT Sedimentary.. 102 sx 10 ag 
FERMI Sea ets a Trenton Limestone weathered aa 91 
Post-Devonian..... ISSSOXT Gp et AURAI er Igneous. .:. ... .30 
TN AT PIM PUR ICE ATEN NACRE RE RARE E eects 8 4.3 
SLA LIT ee Tinguaite (different locality)...| PR Aveta eae 3.0 
is aes Re INepheline Syme uaa sae CAR on ote 125 
Quaternary ........ Boulder GTA VE AN En Sedimentary.. 81 
SA ne Lei Ca ANR ert oc i 95 
sates Lig ges, setts ais eoateene SALON pate coasts. ty .16 
