248 Dr Wilson of% the Decomposition of Water by Platinum 



mercury. Dry oxygen was then added, and the mixture exploded. 

 When the whole had cooled, the walls of the eudiometer appeared 

 dimmed by a very thin layer of moisture, but the quantity of gas 

 operated on, was too small to admit of visible drops being produced. 

 Another portion of the gas was mixed with half its volume of oxy- 

 gen and fired by the electric spark. The contraction which fol- 

 lowed explosion, varied in difierent experiments, but was frequently 

 such as to leave not more than one-twentieth part of the mixed gases 

 unconsumed. Phosphorus smoked in this residue for a short time, 

 shewing that excess of oxygen had been made use of, and left a 

 minute volume of gas which was not diminished by caustic potash, 

 and must have been nitrogen. 



It seemed possible that the trace of carbon present even in malle- 

 able iron, might affect the quality of the gas resulting from the ac- 

 tion of the globules of oxide on water, and that carburetted hydro- 

 gen, carbonic oxide, or carbonic acid might be produced. It seemed 

 desirable to know whether the latter were present or not, as the 

 oxygen might have gone to form them. It was impossible to be 

 certain that carbonic acid was absent, for the gas from the globules 

 being necessarily collected over water, the temperature of which was 

 low, carbonic acid would be retained in solution by that liquid. All 

 that I can say on this point is, that lime-water was not rendered 

 muddy or in the slightest degree opalescent by the gas. It was 

 several times detonated with oxygen over lime-water, but the latter 

 remained quite transparent, so that neither carbonic oxide nor car- 

 buretted hydrogen can have been present. In short, the gas 

 evolved from water by the white-hot globules of oxide of iron, was 

 hydrogen mingled with a small quantity of air, previously no doubt 

 in solution in water. 



As only the hydrogen, then, of the water decomposed was ob- 

 tained, it became necessary to account for the absence of the oxygen. 

 I was tempted for a moment to think it possible that the black oxide 

 of iron might have changed into the red oxide of the same metal, by 

 combining with the oxygen not obtained in the elastic form : ex. gr. 

 thus 2 Feg O4 H- = 3 Fog O3. 



But the proto-peroxide of iron is known to be a very stable com- 

 pound, little if it at all prone to become the peroxide ; and it seemed 

 more likely that unoxidized iron might be present in the fused 

 globules, which occasioned the evolution of hydrogen when it came 

 in contact with water. To ascertain this point, portions of the 

 globules were dissolved in dilute muriatic and sulphuric acids, and 

 were found in most cases to evolve hydrogen. Some specimens of 

 the globules gave off not a trace of gas when they dissolved, and 

 must have consisted of the definite oxide ; a point of interest in con- 

 nection with the fact already mentioned, that globules were frequently 

 observed to drop into water without any bubbles of gas rising from 

 them. 



