232 
Proceedings of the Royal Society of Edinburgh, 
[S 
ess. 
Alundum Tube. 
This tube proved quite unsuitable for tests of this kind. It is so porous 
that it allows air and dust particles to pass through its walls. The result 
is that the test-flask cannot be cleared, but always gives a considerable 
amount of condensation. When, however, the tube was heated to a low 
red, the condensation changed to the woolly type, thus showing a very 
great increase in the number of nuclei. The flame at the same time became 
tinged with orange colour. The increased density of the condensation was 
probably not due to the passage through the walls of the densely packed 
nuclei in the flame, as the increase did not take place till the tube was 
heated to a dull red. The electric charge on the nuclei in the flame 
probably causes them to adhere to the walls of the pores in the tube. 
Difference in temperature would also produce a like effect.* 
Nuclei produced at Ordinary Temperatures. 
In all the above cases where nuclei are produced by heating different 
substances, there are signs of chemical action, or in some cases of physical 
action, causing disintegration at their surfaces and the liberation of small 
particles. This wearing away of the different kinds of matter under the 
influence of hot gases is well known in many industries. Iron bars of 
grates slowly disappear, and the linings of furnaces grow thinner, even 
where there is no friction to account for the loss, and the above experi- 
ments with earthenware tubes seem to indicate that their surfaces are 
carried away in jninute particles. Though this latter form of breaking 
down may not take place to any great extent at ordinary temperatures, 
yet, one naturally asks, may not this production of nuclei occur even at 
ordinary temperatures when there is any chemical action ? 
Phosphorus. 
Phosphorus when exposed to air naturally suggested itself as an ex- 
ample of this, and some experiments were made with it. A very small 
piece, the size of 1 mm. cut off the point of a pin, was attached to the glass 
tube by which the filtered air entered the flask V. It was kept in its 
place simply by the capillarity of the water attached to it. If the air 
was quickly pumped through the flask, the condensation was not too 
dense for testing. The nuclei under these conditions were all small, very 
few being large enough to respond to a 2 per cent, expansion (see test No. 8, 
Table III) ; but there were a number of showers at higher expansions. 
* “ On the Formation of Small Clear Spaces in Dusty Air,” Trans. Roy. Soc. Edin. y 
vol. xxxii, part ii.. 
