Dialytic Separation of Gases by Colloid Septa. 507 



num, 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 platinum 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 consi- 

 derable extent in passing through the heated annular space, hy- 

 drogen passing freely at the same time through the ignited pla- 

 tinum. No trace of undecomposed ammonia, although the gas 

 was transmitted in considerable excess, was discovered accompa- 

 nying 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 mi- 

 nutes, or was sensibly the same as when pure hydrogen was car- 

 ried 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. 



Hydro sulphuric acid. — This gas, prepared from sulphide of an- 

 timony and hydrochloric acid, washed, and dried over chloride of 

 calcium, was then circulated through the outer porcelain tube. 

 The hydrosulphuric acid was nearly all decomposed into sulphur 

 and hydrogen, the latter coming through the platinum at the 

 rate of 9 cub. centims. in five minutes. A trace of hydrosul- 

 phuric acid may also have passed through, as the mercury of 

 SprengeFs tube was slightly soiled; but no indication of this 

 gas could be perceived in the hydrogen collected. It appears, 



