493 
1910-11.] On some Nuclei of Cloudy Condensation. 
ments, but all of them passed the ozone. Asbestos seemed to pass it most 
freely, cotton-wool was next, and curiously glass-wool seemed to check 
more than the others ; but all three held back the active gases for a time, 
probably absorbed by the substance of the filter or condensed on the 
surface of its fibres. But though the filters absorbed the active gases they 
gave them out again, as they required considerable washing with air before 
they were free of them. These three filters did not seem to act equally 
on the different constituents of the ozone tube. For instance, the two test 
papers seemed to be acted on in the same proportion and to the same 
amount when the asbestos filter was used as when no filter intervened ; but 
with the cotton- wool filter, while the iodized starch paper was well darkened, 
the red litmus paper was not changed in the same proportion as it would 
have been if no filter had been used. A filter made of ground charcoal was 
found to hold back all the active gases of the ozone tube ; test papers were 
not discoloured, and even all condensation ceased in the test flask. Wet 
cotton-wool acts like carbon, and destroys all the products of the ozone tube. 
In these tests with ozone and other substances glass flasks were generally 
used, though some tests were made with a silica flask at an open window 
to get the maximum light effect. It was found, however, that glass flasks 
sunned through a window gave working results. Glass connecting tubes 
were generally used, the ends being brought close and joined by a short 
length of india-rubber tube. India-rubber stoppers were generally used in 
the flasks. Some tests were made to see if the rubber had any effect on the 
gases and vapours used in the experiments. Pieces of rubber were put into 
the sunning flask and subjected to the conditions of the experiment, but no 
effect was observed. Another test was made to see if the action of ozone on 
rubber had any tendency to produce nuclei. The ozone tube was first 
connected direct with the test flask by means of a new piece of glass tube, 
all stopcocks, etc., being removed, as they might influence the results ; there 
was only one joint between the ozone tube and the test flask, and that 
was made by entering the one tube some distance inside the other and 
sealing the outside. The density was then noted of the condensation 
produced by a certain number of sparks of a fixed length given to excite 
the ozone tube. After a number of trials, and density of condensation noted, 
the joint between the ozone tube and the test flask was broken and the ends 
of the two tubes were connected by means of a rubber tube 1J metres long. 
Though the ozone had to travel through all that length of rubber tubing, no 
difference was noted in the density of the condensation in the test flask. 
It would thus appear that, though ozone is known to act on rubber, this 
action does not result in the production of nuclei; we may therefore 
