487 
1910-11.] On some Nuclei of Cloudy Condensation. 
in the test-flask, nor did it do so when salt and iodine were added. The 
investigation of hydrochloric acid was, however, continued; and, though not 
directly hearing on our subject, the results seem to be of sufficient interest 
to be recorded. With this acid the well-known condensing powers of newly 
prepared gases were investigated. For this purpose the same apparatus was 
used as before, with the addition of two metal wires which passed through 
the stopper of the sunning flask ; one of these wires terminated in a thick 
copper wire, the other in a strip of amalgamated zinc about 3 mm. broad. 
The copper wire and zinc plate dipped about 3 mm. into the weak solution 
of hydrochloric acid in the flask. If the wires outside the flask were not 
connected, so that no gases were generated, then as before there was no 
condensation after sunning ; but if the wires were brought into contact for 
a few seconds so as to liberate a little hydrogen, and the gases sunned for 
one minute, then very dense fogging took place when tested. If the gases 
were kept in the dark there was no condensation on testing, only a few 
drops appearing such as might be expected from the bubbling of the gases 
at the pole of the battery ; but if these same gases formed in the dark were 
afterwards sunned they gave dense fogging. It may be stated that the 
zinc and copper couple may be outside the sunning flask and the gases 
drawn in through the cotton-wool filter F. The density of the con- 
densation so produced shows that the gases have passed freely through 
the filter. 
These experiments seemed to indicate that the hydrogen escaping from 
the small battery had in a very high degree the clouding tendencies usually 
ascribed to newly prepared gases. It was therefore necessary to investigate 
further, as in other experiments I had found very little tendency in newly 
prepared gases to cause condensation. Great precautions were taken in the 
next experiments. New flasks, etc., were used and everything done to ensure 
purity. With the new apparatus the hydrochloric acid and newly prepared 
hydrogen no longer responded to sunshine, so experiments were made to 
find out what had caused them to be sensitive in the previous tests. As 
iodine had been in the flasks previously used, it was suspected. A minute 
trace of that substance added to the hydrochloric acid, or admitted to the 
flask as a vapour, at once made the gases active and caused dense fogging. 
Further, one of the old flasks in which iodine had been experimented with 
was first washed with alcohol and afterwards carefully with water, yet on 
using this flask in place of the new one it gave dense condensation with 
hydrochloric acid and hydrogen, showing that enough iodine had remained 
on the washed walls of the flask to make the gases respond to the action of 
sunshine. This shows that though the newly prepared hydrogen was not 
