418 
DR. E. FRANKLAND ON A NEW SERIES OF 
metallic compounds are two, viz. heat and light ; in many cases either of these can 
be used, in others only one can be made to effect the desired combination, whilst 
more rarely the assistance of both appears to be essential. In those experiments in 
which heat was employed the materials were subjected to its action in sealed glass 
tubes, about 12 inches long, and varying in diameter from half an inch to 1 inch, 
the thickness of the glass being about one-eighth of an inch*. To preserve the gaseous 
products of the operation in a state of perfect purity for subsequent investigation, the 
tubes were well exhausted before being sealed ; they were then immersed to about 
half their depth in an oil-bath, and heated to the required temperature. In cases 
where the influence of light was employed, the materials, confined in tubes of pre- 
cisely similar dimensions, were exposed to the sun’s rays, concentrated in most cases 
by an 18-inch parabolic reflector, near the focus of which the tubes were placed, either 
naked or surrounded by a solution of sulphate of copper to absorb the calorific rays. 
By this arrangement the light and heat could be increased, diminished or modified 
at pleasure, which was found very convenient in several of the operations. 
Action of Tin upon Iodide of Ethyl. 
When iodide of ethyl and metallic tin are exposed to the action of either heat or 
light, the tin gradually dissolves in the ethereal liquid, which finally solidifies to a 
mass of nearly colourless crystals. This reaction is effected most conveniently by the 
action of light, an excess of tinfoil, cut into narrow slips, being employed : the sealed 
tubes containing these ingredients should be placed near the focus of a large para- 
bolic reflector, the temperature being prevented, if necessary, from rising too high 
by immersing them in water or in a solution of sulphate of copper. The unconcen- 
trated rays of the sun, or even diffused daylight, are quite sufficient to determine the 
formation of the crystalline body ; but an exposure of several weeks, or even months, 
would be necessary for the completion of the change, which is effected by the use of 
the reflector in a few days of bright sunshine. The liquid gradually assumes a straw- 
yellow colour, but its solidification is prevented as long as possible at the end of the 
operation, by allowing the temperature to rise 20° or 30° C. above that of the atmo- 
phere ; thus nearly the whole of the iodide of ethyl becomes united with tin. When 
heat instead of light is employed to effect the combination, the tubes should not be 
more than half an inch in diameter, and to avoid the risk of explosion, should not be 
more than one-fourth filled with the materials : the combination takes place at about 
180° C. The agency of heat is therefore much less convenient than that of light in 
the production of this reaction, which is also never so complete as when the latter 
agent is employed ; I have satisfied myself, however, that the results are the same in 
both cases. 
* A minute account of the construction and use of these tubes is given in the Journal of the Chemical 
Society, vol. ii. p. 265. 
