of charcoal and hydrogen. 145 
considered, therefore, as quite essential to the mutual agency 
of these gases, that they should be subjected to the influence 
of light. But it is not necessary that the direct rays of the 
sun should fall on the mixture, the light of a dull and cloudy 
day being fully adequate to the effect. On a day of this sort, 
I filled several stoppered vials, graduated into hundredths 
of a cubic inch, with a mixture of 30 volumes of carburetted 
hydrogen with from 80 to 90 of chlorine, and uncovering 
them all at the same moment, exposed them to the feeble 
light which was then abroad. By exposure of one of the 
vials during half a minute, no diminution of volume was 
found to have been effected ; another vial, opened under 
water when one minute had elapsed, showed an absorption 
of five parts ; a third in two minutes had lost 15 parts ; a 
fourth in four minutes 25 parts ; and a fifth, opened in five 
minutes, contained only 50 volumes out of the original 110. 
The products, resulting from the contact of carburetted 
hydrogen and chlorine, under circumstances favourable to 
their mutual action, have been described by Mr. Cruick- 
shank, with whose experience on this point my own entirely 
agrees When rather more than four volumes of chlorine 
are kept in mixture with one volume of gas from stagnant 
water, the products are muriatic acid gas, and a volume of 
carbonic acid equivalent to that of the pure carburetted hy- 
drogen ; and this, whether the mixture be exposed to direct 
or indirect solar light ; the only difference being that the 
less intense the light, the more slowly is the effect produced. 
When less than four volumes of chlorine are employed, the 
residue consists of muriatic and carbonic acids, carbonic oxide, 
mdcccxxi. U 
