14 



NATURE 



[December 28, 1893 



Inactive. 

 Air, &c., in which electrical discharge has ceased for about 

 ten seconds. 



Smoke without fire. 



Bottled phosphorus fumes. 



Ammonia. 



Ozone. 



Steam. 



Alcohol vapour. 



Formic acid vapour. 



Sulphurous acid. 



It seems that we have here a pretty little problem which 

 might, perhaps, be solved without much difficulty by a com- 

 petent chemist, but which quite baffles me.^ Is it possible that 

 the condensing vapours may contain dissociated atoms? 



To return to the electrical effect. There are only two kinds 

 of chemical change that I know of which could be brought 

 about in air by an electrical discharge. Either some of the 

 oxygen might be converted into ozone, or the oxygen and 

 nitrogen of the air might be caused to combine, forming nitric 

 acid or some such compound. The former of these would 

 not account for the action of the air upon the jet, because, 

 as we have seen, ozone is inoperative ; the latter migbt. 

 But if the activity of the air is due to the presence in it of a 

 compound of oxygen and nitrogen, then it is clear that an 

 electrical discharge in either nitrogen or oxygen separately 

 would fail to render those gases active. 



I arranged a spark bottle, inside which an induction-coil dis- 

 charge could be made to take place ; two bent tubes were 

 passed through the cork, one reaching nearly to the bottom for 

 the ingress of the gas to be tested, the other, a shorter one, for 

 its egress. The open end of the egress tube was fixed near the 

 steam jel, and first common air, then oxygen and then nitrogen 

 were successively forced through the bottle while the coil dis- 

 charge was going on. All produced dense condensation, but 

 I thought that oxygen appeared to be a little more efficient than 

 common air, and nitrogen a little less. 



This last experiment points to a conclusion to which at pre- 

 sent I see no alternative. It is that the action on the jet of an 

 electrical discharge is due in some way or other to dissociated 

 atoms of oxygen and nitrogen. There is nothing else left to 

 which it can be due. 



So far as Robert Holmholtz's explanation coincides with this 

 conclusion, I think it must be accepted as correct. As to the 

 precise manner in which he supposed the dissociated atoms to 

 act upon the jet, it is more difficult to agree with him. He 

 thought that the abnormal condensation was a consequence of 

 the molecular shock caused by the violent recombination of the 

 dissociated atoms in the supersaturated air of the jet, the action 

 being analogous to that which occurs when a supersaturated solu- 

 tion of sulphate of soda, for example, is instantly crystallised 

 by a mechanical shock. 



To me this hypothesis, ingenious as it is, seems to be more 

 fanciful than probable, but I can only hint very diffidently at 

 an alternative one. To many chemical processes the presence 

 of water is favourable or even essential. Is it possible 

 that the recombination of free atoms may be assisted by water ? 

 And is it possible that dissociated atoms in an atmosphere of 

 aqueous vapour may obtain the water needed for their union 

 by condensing it from the vapour ? 



According to Holmholtz, flames and incandescent substances 

 generally cause dissociation of the molecules of oxygen and 

 nitrogen in the surrounding air. This, I believe, is generally 

 admitted. I do not know whether slowly oxidising phosphorus 

 has the same effect. 



If it is conceded that the atmospheric gases are dissociated by 

 electrical discharges, and that the presence of such dissociated 

 gases somehow brings about the dense condensation of water 

 vapour, we may still regard the electrified steam jet as affording 

 an illustration of the abnormal darkness of thunder-clouds. 



Perhaps another source of dissociated atoms is to be found in 

 the ozone which is generated by lightning flashes. A molecule 

 of ozone consists of three atoms of atomic oxygen, while one of 

 ordinary oxygen contains only two. Ozone is an unstable kind 

 of material, and gradually relapses into ordinary oxygen, the 

 process being that one atom is dropped from the three-atom 

 molecules of ozone, these detached atoms in course of time 



Two chemists of the highest eminence have been good enough to con- 

 sider the problem for me, but they are unable to throw any light upon it. 



NO. 1 261, VOL. 49J 



uniting with one another to form pairs. Thus two molecules 

 of ozone are transformed into three of oxygen. A body of ozone 

 is therefore always attended by a number of dissociated atoms 

 which are looking for partners. 



In the steam jet experiment there is not time for the dis- 

 engagement of a sufficient number of isolated atom.s from a blast 

 of ozone to produce any sensible effect. But the case is otherwise 

 when the vapour is confined in a closed vessel, as in Mascart's 

 experiment, or when it occurs in the clouds, where the movement 

 of air and vapour is comparatively slow. 



Ozone, it will be remembered, was found by Mascart to pro- 

 duce dense condensation in a closed vessel even after being 

 filtered through cotton wool. Similar filtration seems to entirely 

 deprive the so-called products of combustion of their active 

 property, a fact which has been adduced as affording over- 

 whelming evidence in favour of the dust nucleus theory. Coulier 

 himself, however, detected a weak point in this argument. He 

 produced a flame which could not possibly have contained any 

 products of combustion except steam, by burning pure filtered 

 hydrogen in filtered air ; yet this product was found to be per- 

 fectly capable of causing dense condensation, and, as in his 

 former experiments, filtration through cotton wool deprived it 

 of its activity. 



These anomalies may, I think, be to a great extent cleared up 

 if we assume that the effect of the cotton wool depends, not upon 

 the mere mechanical obstruction it offers to the passage of 

 particles of matter, but upon the moisture which it certainly 

 contains, and which may act by attracting and facilitating the 

 reunion of dissociated atoms before they reach the air inside 

 the vessel. According to this view ozone would remain an 

 active condenser in spite of its filtration, because free atoms 

 would continue to be given off by it after it had passed the cotton 

 wool. The filtration experiment should be tried with perfectly 

 dry cotton wool, which, however, will not be easily procured, 

 and if my suggestion is right, dry wool will be found not to 

 deprive ordinary products of combustion of their condensing 

 power. 



To sum up. I think my recent experiments show conclusively 

 that the dense condensation of the steam jet is not due directly 

 either to electrical action or to dust nuclei. The immediate 

 cause is probably to be found in dissociated atoms of atmospheric 

 gases, though as to how these act we can only form a vague guess. 



ShELFORD BlDWELL. 



SCIENTIFIC SERIALS. 



American journal of Science, December. — An apparent time- 

 break between the eocene and Chattahoochee miocene in south- 

 western Georgia, by Raphael Pumpelly. The Red Clay Hill 

 region, a plateau extending through the south-western part of 

 Georgia and adjacent northern Florida, has a maximum altitude 

 of 300 feet, is sharply limited on the north by a declivity facing 

 the eocene flat-land country, and consists of miocence deposits 

 resting on eocene, both of which dip about 13 feet per mile to 

 the south. The base of the plateau is formed by the white 

 calcareous beds of the Chattahoochee group. A time-break 

 between the latter and the eocene is evidenced by the almost 

 general presence of a limestone conglomerate at the base of the 

 Chattahoochee, immediately overlying eocene fossils, and the 

 irregularity of the surface of demarcation. It seems possible 

 that during miocene time the present plateau of southern Georgia 

 was outlined by submerged islands of the eocene limestone. The 

 Gulf Stream, after the creation of the central American 

 barrier, found its way back to the Atlantic sweeping over 

 southern Georgia and northern Florida, and supplying the 

 food needed to build up the great organic beds of the Chat- 

 tahoochee and Chipola. The lower flat-land country of 

 central Georgia may represent the contemporaneous course of 

 the cold current carrying less pure water and less nutriment. 

 — The rise of the mammalia in North America, by H. F. 

 Osborn. This second part deals with ancient and modern pla- 

 cental differentiation, the succession of the perissodactyls and 

 the ariiodactyls, a discussion of the factors of evolution, and a 

 diagram illustrating the supposed descent of the mammalia from 

 their Jurassic prototypes. — On the thoracic legs of Triarthrus, 

 by C. E. Beecher. Some very perfect specimens of Triarthrus 

 Becki, Green, in which nearly the entire calcareous and chitinous 

 portions are represented by a thin film of iron pyrites, show, 

 besides the antennae already noticed, a complete series of thor- 



