1904-5.] Opacity of Aluminium Foil to Ions from a Flame. 903 
On the Opacity of Aluminium Foil to Ions from a Flame. 
By George A. Carse, M.A., B.Sc., 1851 Exhibition Science 
Research Scholar of Edinburgh University; Emmanuel Col- 
lege, Cambridge. 
(Read July 17, 1905.) 
The apparatus used to show that aluminium was opaque to the 
ions from a flame consisted (see fig. 1) of a tube A, which was 
Fig. 1. 
funnel-shaped at one end, the other end of which led to an 
enclosure B, one side of which (a b) was made of aluminium foil 
connected to earth, and on the other side there was an insulated 
metallic plate (cd), which could either be connected to earth 
or to a high potential battery. On the other side of the 
aluminium foil there was an electroscope in a closed case C. 
The electroscope was of the type used by C. T. R. Wilson* 
in his experiments on the natural ionisation of air in closed 
vessels. 
The ions were got from a bunsen burner placed beneath the 
funnel, the heated air being cooled by a water-jacket D, and 
* Proc. Roy. Soc., 68, p. 152, 1901. 
