1896 - 97 .] Experiments on Electric Properties of Uranium. 421 
the deviation was -f 0‘8 of a volt, with aluminium- water-uranium 
it was + 043 of a volt.* 
§ 30. Uranium-conductance-zero in different gases and at dif- 
ferent atmospheric pressures. 
To investigate the behaviour of uranium in different gases and 
at different atmospheric pressures another piece of uranium 3 cms. 
long, 1 cm. broad, and ^ cm. thick, was mounted firmly in a glass 
bulb 6 cms. long, 3 cms. diameter on a platinum electrode fused into 
one end of the bulb. The uranium in the glass bulb was sur- 
rounded throughout two-thirds of its length by a zinc cylinder 
.14 cm. in diameter. This zinc cylinder was kept in position by a 
stiff platinum electrode fused into the other end of the glass (see 
diagram 7). Two glass tubes were fixed on to the bulb, one at 
each end ; by -means of these any desired gas could be introduced, 
or any desired vacuum could be obtained. 
The gas used was first stored in a reservoir over water. It was 
then bubbled through strong sulphuric acid and drawn over 
caustic potash, calcium chloride, and phosphoric anhydride into 
the glass bulb. The bulb was first exhausted to an atmospheric 
pressure of about 6 mms. ; then the gas to be used was passed 
into it. This was repeated about twenty times. Finally it was 
strongly heated so as to drive off any adhering layers of gas, and 
then allowed to cool in an atmosphere of the gas at 760 mms. 
* On the other hand, when the uranium surface was covered with water to 
the depth of about a millimetre, and an air space left between the wet uranium 
surface and the opposed insulated metal, so that we had a uranium-water-air- 
metal arc, the rate of deviation -from the metallic zero was reduced so much as 
to be scarcely appreciable. 
