172 -Dr. Henry on the Aeriform Compounds [Sept. 



by Dalton.* It does not, however, appear to have been ascer- 

 tained by either of them, whether the complete exclusion of 

 light prevents any degree of action of chlorine and carburetted 

 hydrogen on each other. I mixed, therefore, those two gases 

 in different proportions in well stopped vials, which were com- 

 pletely filled with the mixture, and covered by opaque cases. 

 When the stoppers were removed under water, at various inter- 

 vals after the mixture, from a few minutes to 39 days, no dimi- 

 nution whatever of volume was found to have taken place ; and 

 after having removed the chlorine by liquid potash, the carbu- 

 retted hydrogen gas gave the usual products of carbonic acid, 

 and consumed the usual proportion of oxygen. Mixtures also 

 of hydrogen and chlorine, and of carburetted hydrogen and 

 chlorine, standing over water in graduated tubes, which were 

 shaded by opaque covers, sustained no loss of bulk, except what 

 arose from the absorption of chlorine by the water, the combus 

 tible gas remaining wholly unaltered. It may be 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 ade- 

 quate to the effect. On a day of this sort, I filled several stop- 

 pered 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 absorp- 

 tion 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 hydro- 

 gen and chlorine, under circumstances favourable to their mutual 

 action, have been described by Mr. Cruickshank, 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 hydrogen ; 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, and undecomposed carburetted hydrogen, the 

 proportions of the two last increasing as, within certain limits, 

 we reduce the relative quantity of chlorine. These changes. 



* New System of Chemical Philosophy, p. 300. 



