492 Proceedings of the Royal Society of Edinburgh. [Sess. 
or iodine, be put on the platinum point, a very dense condensation is 
produced with very slight electrification. 
Ozone Tube. 
Experiments were also made with ozone prepared by means of a 
Siemens ozone tube. A small coil and one-cell bichromate battery, or a 
small induction electrical machine with two ebonite plates, was used for 
exciting the tube. The results were similar to those obtained with the 
point discharge, which probably owes most of its action to the production 
of ozone. With the electrical machine sparks of 3 mm. could be given 
without producing any nuclei if the sunning flask was clean ; but whenever 
salt or iodine was in the flask, dense condensation took place in the test 
flask if the gases were sunned, but none without sunning. 
In making these experiments with ozone it was soon found that the 
cleanness of the sunning flask was of great importance. Indeed, it is not 
certain that the condensation which takes place with the higher potentials 
is not due to some impurity in the flask, as it has been found that the 
more care taken in cleaning this flask the higher the potential from the 
point discharge, and for working the ozone tube, that may be given without 
producing nuclei. In the experiments with the ozone tube it was found 
that damp air gave nuclei with a potential discharge that gave none when 
the air was dry. This result was also obtained in the point discharge 
experiments. 
The product of the Siemens tube seems to vary with the potential 
and density of the charge, which is what one might expect, as its product 
is of a mixed kind and the proportion of ozone to the other products does 
not seem to be constant. 
Tests were made to see if the products of the electric discharge in 
the Siemens tube were particles or gases. For this purpose the air from 
the tube was passed through a filter, then through a tube in which were 
placed some ozone test papers, the air being then led into the test flask. 
On exciting the ozone tube somewhat strongly and drawing the air through 
the apparatus into the test flask, it was noticed that no effect was at first 
produced on the test papers, nor did any condensation make its appear- 
ance in the test flask ; but after two or three strokes of the pump the test 
papers got rapidly discoloured and dense condensation took place in the 
test flask. The test papers used were the iodized starch and the red 
litmus moistened with potassium iodide, which seems to be the best test 
paper for ozone, as it turns blue on the liberation of the alkali and is 
unaffected by acids. Different kinds of filters were tried in these experi- 
