DIALTTIC SEPARATION OF GASES BY COLLOID SEPTA. 437 



(2) In fifteen minutes, 7*17 cub. centims., containing 0-52 cub. centim. or 7-2 per cent, 

 of carbonic acid. The gas of this and the following stages of observation now burnt with 

 a blue flame, and was principally carbonic oxide. 



(3) In thirty minutes, 10-4 cub. centims., of which 6-86 cub. centims. were carbonic 

 oxide. 



(4) In thirty minutes, 8-16 cub. centims., of which 0-12, or 1-4 per cent., was carbonic 

 acid. 



(5) In thirty minutes, 5-52 cub. centims., of which 0*03 was carbonic acid — that is, O'u 

 per cent. 



Hence 46 grms. of wrought iron have in two hours given off" 46*85 cub. centims. of 

 gas, measured at about 15° C. ; or 1 volume of iron has discharged 7*94 volumes of gas, 

 of which about two-thirds was carbonic oxide ; and the metal does not appear to be yet 

 quite exhausted. Iron is a metal not unlikely to contain small quantities of carbon and 

 oxygen, both in chemical union with iron ; and the gas extricated may partly be due to 

 a reaction of these elements upon each other at a red heat. 



2. In another similar experiment upon 32 grms. of clean iron wire (No. 21), measuring 

 4'1 cub. centims., the iron was heated in a small glass tube, to exclude the idea of the 

 conceivable permeability of the porcelain tube. The iron gave off gas at a pretty uniform 

 rate, which amounted in an hour to 29'8 cub. centims., of which 4*44 cub. centims. were 

 carbonic acid, and the remainder principally carbonic oxide, with hydrogen and a trace 

 of a hydro-carburet. Here the iron wire gave off 7 "2 7 volumes of gas. 



3. In a third experiment on thin iron wire (No. 23), the extrication of the natural 

 gases at a red heat was pushed to a greater degree of exhaustion. The weight of the 

 iron was 39 grms., and its volume 5 cub. centims. In the first and second hour the gas 

 collected was 45 cub. centims. ; in the third hour 10"85 cub. centims. ; in the fourth 

 and fifth hours 5'65 cub. centims. ; in the sixth hour 0'9 cub. centim., and in the seventh 

 hour 0"7 cub. centim. The iron appears to be now nearly exhausted, after the extrica- 

 tion of 63'1 cub. centims., or 12 55 volumes of gas. 



It is evident that iron cannot be safely dealt with in experiments upon the permeation 

 or upon the absorption of gases, till these gases, whether self-produced or preexisting, 

 are first extricated from the metal. The carbonic oxide observed in the tube experiments 

 of M. Deville may have been derived from the same source*. 



4. To observe the absorption of hydrogen, tlie mass of exhausted iron wire remaining 

 after the last experiment was heated to redness, and cooled gradually in the same gas. 

 The metal was afterwards freely exposed to air (as usual) to get rid of any loosely 

 attached hydrogen. Now exhausted again by the Sprengel pump at a low red heat, the 

 iron gave 2-5 cub. centims. of gas in one hour, but the greater portion in the first ten 

 minutes, consisting of 



*. The gases -which escape from east iron in a state of fusion have been examined by M. L. Cailletet. They 

 appear to contain from 49 to 58 per cent, of carbonic oxide, 34 to 39 of hydrogen, and 8 to 12 x)f nitrogen. — 

 Comptes Rcndus, t. Lsi. p. 850 (1865). 



