516 
HON. E. J. STEUTT ON THE CONDUCTIVITY 
The oljservations on hydrochloric acid gas are not to he relied on. This gas 
rapidly attacked the metal of which the apparatus was made. The chlorine no 
doubt comlnned with the metal, setting the hydrogen free. The pressure rapidly 
diminished if the apparatus was left standing full of the gas. No doubt the difficulty 
inight liave been avoided by using an apparatus of platinum, but it was thought 
hardly wortli while to go to the trouble and expense which this would have involved. 
It is to he regarded as a matter of accident that the separate determinations agree 
with one another as well as they do. In the other cases I believe the mean re.sults 
are not, for the most part, more than 2 per cent, from the truth, if so much. 
The discussion of these results, as well as those that follow, will be deferred till the 
end of the paper. 
It will be worth while to mention that the conductivities of hydrogen and air were 
compared when an additional sheet of copper, equal in thickness to that which 
formed the bottom of the vessel ('007 centim.), was used to cut down the radiation. 
Almost exactly the same ratio as befoi'e was found. So far as this propert}^ is con¬ 
cerned, the radiation whicli penetrates one sheet of copper '007 centim. in thickness 
is homoo'eneous. 
o 
§ 5. Easily Ahsorhahle Rays from Radio-active Barium Carhonate. 
To investigate the easily absorbable rays, the second form of apparatus was used, 
the radiating body being in contact with the gas under investigation, without the 
interposition of any solid partition. The radiation from the barium compound is 
enormously reduced by the interposition of so thin a screen as an ordinary piece of 
tinfoil; these “ soft ” rays accordingly form much the greater part of the whole. 
They cannot be conveniently separated from the penetrating rays used in the above 
experiments, but these latter are present in so small a proportion that they do not 
much affect the results (see above, p. 508). As is there mentioned, there is a differ¬ 
ence in kind as well as in degree between the behaviour of the two types of rays. 
The penetrating I’ays are deflected by the magnet; the others are not so. 
The barium compound was so very active that even when a very small quantity 
was taken, and the air pressure considerably reduced, the rate of leak was much too 
large for convenient observation. A parallel plate condenser was accordingly con¬ 
nected to tlie electrometer so as to increase its capacity. The distance between the 
plates was adjusted till the lute of leak had a convenient value, and was not after¬ 
wards altered. This plan is much better in practice than diminishing the sensitive¬ 
ness of the electrometer by lowering the potential of the needle. 
The rate of leak in air was determined at various pressures. 
