418 ME. T. GEAHAM ON THE ABSOEPTION AND 



of pure hydrochloric acid, the gas being afterwards washed with water and dried by- 

 sulphuric acid in its way to the exterior porcelain tube. In one hour the interior 

 platinum tube yielded only three-tenths of a cubic centimetre of gas, of which, again, 

 only an indeterminate small portion was condensed by baryta water and appeared to be 

 carbonic acid. The passage of carbonic acid is therefore incalculably small at a full 

 red heat. 



Chlorine. — This gas, evolved slowly from a glass flask containing peroxide of manga- 

 nese and hydrocliloric acid, was washed by water, dried by sulphuric acid, and thrown 

 as usual into the porcelain tube so as to occupy the annular space between the two 

 tubes. A small tube containing slaked lime was interposed between the end of the plati- 

 num tube and the Sprengel pump, so as to absorb the chlorine, if any came through 

 the substance of the platinum. After the tube had been heated for an hour, the lime 

 was examined for chlorine, but did not contain a trace of that substance. A minute 

 quantity of gas, probably air, amounting to 0"15 cub. centim., was collected during the 

 time. Platinum, then, is not sensibly penetrated by chlorine at a red heat. 



Hydrochloric acid, dried over sulphuric acid, was passed for one hour through the 

 porcelain tube. About 0-5 cub. centim. of gas was collected from the platinum tube, 

 which contained no hydrochloric acid and no free hydrogen. The ignited platinum, 

 then, is not penetrated by hydrochloric acid ; nor does it appear to dissociate the 

 elements of that gas at the temperature of the experiment. 



Vapour of water. — A stream of steam was carried for one hour through the porcelain 

 tube. During that time half a cub. centim. of gas appeared to be drawn from the plati- 

 num tube, which gas contained no hydrogen. There is no evidence of the passage 

 through the platinum of the vapour of water, nor of its decomposition. 



Ammonia. — This gas appeared to be decomposed to a considerable extent in passing 

 through the heated annular space, hydrogen passing freely at the same time through 

 the ignited platinum. No trace of undecomposed ammonia, although the gas was trans- 

 mitted in considerable excess, was discovered accompanying the free hydrogen found in 

 the platinum tube. When the ammonia was evolved slowly, the quantity of hydrogen 

 entering the platinum tube amounted to 16-4 cub. centims. in five minutes, or was sen- 

 sibly the same as when pure hydrogen was carried through the annular space. Ammonia, 

 then, appears to be incapable of penetrating the ignited platinum. 



Coal-gas. — When coal-gas was carried through the porcelain tube, the following 

 quantities of hydrogen came through the platinum in successive periods of twenty 

 minutes each, 13-3 cub. centims., 5*2, and 8"8. The first portion, when exploded with 

 oxygen, did not disturb baryta-water after condensation; 13-3 cub. centims. contained 

 13-16 cub. centims. of hydrogen. It appears, then, that the permeating gas was free 

 hydrogen only, and that no compound of carbon present in coal-gas was capable of 

 passing through the platinum. This may be held as excluding the passage of carbonic 

 oxide, marsh-gas, and olefiant gas, all represented in the coal-gas. 



Hydrosulphuric acid. — This gas, prepared from sulphide of antimony and hydrochloric 



