GASEOUS D1FFCSIO3T.] 



METEQKOLOGY. 



1121 



upper one being filled with hydrogen gas, the lower one 

 with oxygen gas, placed in com- rig. i. 



inunication with each other by 

 a capillary tube passing through 

 the cork stopper of both, and 

 allowed to remain at rest for fc 



about half an hour, perfect mix- 

 ture of the oxygen and hydro- 

 gen gases will have ensued. In- 

 asiuuch as no chemical union 

 takes place between the two 

 gases thus circumstanced, and 

 as hydrogen gas, filling the upper 

 vessel, weighs but ^th of its 

 bulk of the oxygen gas filling 

 the lower vessel, some new cause 

 of admixture has to be sought ; 

 it depends upon the mutual tendency of the two gases 

 to become diffused through each other. 



The above is an individual case exemplifying a general 

 principle ; any two gases might have been selected, and 

 mutual diffusion would have ensued. Oxygen and 

 hydrogen gases have been here chosen, because of the 

 facility wherewith the circumstance of these having be- 

 come diffused, may be determined. It is well known 

 that neither oxygen nor hydrogen gas, taken separately, 

 will explode on the application of tlaine, whereas a mix- 

 ture of the two readily explodes ; hence the propriety of 

 electing these two gases for illustration of the principle 

 in i|Uestion, will be obvious. 



Faraday appears to have been the first to direct atten- 

 to the mutual diffusibility of gases. He noticed 

 that bottles filled with gases, and corked or stoppered, 

 or vessels filled with gases and inverted over mercury, in 

 either case enclosed to all appearance accurately, never- 

 theless almost always permitted mutual admixture of the 

 air without and the gas within. Dobereiner, Mitchell, 

 and Graham, more especially the latter, have since in- 

 vestigated this class of phenomena more narrowly ; and 

 Graham has succeeded in determining the law which re- 

 gulates tliis diffusion. He finds that the relative dif- 

 fusiveness of any two gases is expressed by the reciprocals 

 of the square root of their densities. Thus, the density 

 of air being one, its diffusiveness is one also. The density 



of hydrogen being 0-693, its diffusiveness is -;rgga = 

 6 ; 233 = ** ' tne deusity * a'B'nonia being 0-5898, its 



diffusiveness is 



= 1 30 ; and generally 



1 



/06898"o-7081 

 representing the density of a gas by d, its diffusiveness is 



= , , Applying this rule to practice, it appears that, 



supposing hydrogen and ammonia placed under circum- 

 stances promoting their mutual diffusion, 3-8 volumes of 

 hydrogen will become mingled with 1 '30 of ammonia. 



It will be remarked that the atmosphere has hitherto 

 been treated of, in a theoretical sense, as a mere mixture 

 of nitrogen and oxygen gases. Practically, however, the 

 atmosphere is far more complex. It invariably contains 

 portions of carbonic acid (about one part in a thousand) ; 

 also extraneous gases, besides aqueous and other vapours. 

 A mixture of all these things may be termed, distinctively, 

 the actual or practical atmosphere. They will hereafter 

 come under our notice teriatim; but even a theoretical 

 mixture of oxygen and nitrogen gases is subject to re- 

 markable variations of property, its chemical composi- 

 tion remaining unchanged ; portions of its oxygen are 

 subject to be converted into uzone. 



The change of common oxygen into ozone, furnishes an 

 'ration of one of the most remarkable discoveries of 

 modern science. It displays what is, perhaps, the most 

 extraordinary example of the condition of allotropitm, 

 or the existence of one body under two different aspects ; 

 it promises to render evident some of these occult atmo- 

 spheric causes which determine the progress of epidemics, 

 and promote the existence of cu>lernic diseases. 



VOL. i. 



A summary of our knowledge relative to ozone may 

 be briefly stated as follows : Oxygen gas is susceptible 

 of undergoing a change, the nature of which is altogether 

 veiled in mystery. It is susceptible of becoming odorou-j, 

 corrosive, and irritating when breathed ; its chemical 

 action may be exalted and modified, so that, whilst or- 

 dinary oxygen gas neither bleaches nor corrodes silver, 

 nor decomposes iodide of potassium, the allotropic, or 

 second form of oxygen gas, will accomplish all these re- 

 sults, and many more too numerous for mention here. 

 The general conclusion to which it is desired to bring 

 the reader is this : if causes can be proved to exist 

 capable of changing atmospheric oxygen gas, in its or- 

 dinary state, into oxygen gas in its extraordinary state, 

 how vast, how complicated must be the meteoric results 

 determined thereby ! That such natural causes do exist, 

 will be readily inferred from a consideration of the arti- 

 ficial methods to which the chemist has recourse, for 

 changing ordinary oxygen into ozone. 



METHOD OF OZONISING OXYOKN GAS. The most readj- 

 method of ozonising oxygen gas is as follows : Take a 

 few sticks of phosphorus ; scrape them free from all 

 superficial oxide, <tc. ; place them in a wide-mouthed 

 bottle containing a little water, but not enough to cover 

 the phosphorus. Let the whole remain at rest for about 

 ten or fifteen minutes, and a considerable portion of the 

 atmospheric oxygen will have been converted into ozone. 

 The ozonised air thus generated will be at present mixed 

 with vapours of phosphorus acid ; washing will free the 

 air from these, however, without removing the ozone. 

 That the air thus treated has become considerably modi- 

 fied in some way, will, in the first place, be rendered 

 evident by the smell. Atmospheric air, when pure and 

 in its ordinary state, is devoid of smell ; but the atmo- 

 spheric air, the product of the experiment just detailed, 

 will be found to have a very peculiar odour. It will be 

 found, moreover, to be capable of removing the colour 

 of sulphate of indigo, and other vegetable and animal 

 colouring bodies. All this is due to the modification 

 which ordinary oxygen gas assumed due to its assump- 

 tion of the allotropic state to its conversion into ozone. 



Another ready method of generating ozone is this : 

 Moisten the interior of a bell-glass receiver, or a large- 

 mouthed bottle, with ether ; then take a glass rod, heat 

 it in the flame of a spirit-lamp, and plunge it into the 

 bottle or bell-glass : under these circumstances ozone will 

 be formed, provided the glass rod has not been heated 

 to a very high temperature ; for the circumstance has to 

 be mentioned, that ozone is reconverted into ordinary 

 oxygen gas by contact with any body heated above a 

 certain, but not very well-determined point. 



We have seen that the ordinary method of generating 

 ozone, consists in bringing phosphorus into contact with 

 atmospheric air (or oxygen) under certain conditions. 

 Many other substances besides phosphorus are capable of 

 generating ozone by contact. Oil of turpentine, and 

 many other essential oils, will accomplish this ; and the 

 fact in question cannot be too forcibly remembered by 

 the painter, who may discover, in the philosophy of ozone, 

 the reason why certain pigments fade, or are bleached, 

 thus destroying the general effect which he desired to 

 produce. Meteorologically considered, however, the 

 most important source of ozone remains to be described : 

 we refer to the production of ozone by means of elec- 

 tricity. Every person who has been much accustomed 

 to work with the electrical machine, must have noticed 

 the generation of something powerfully odorous during 

 the friction of the cylinder, or plate, against the rubber. 

 This odour has, in point of fact, been called the electric 

 tmell. Now, if this electric smell be compared with the 

 smell of the atmospheric air which has been treated witli 

 phosphorus, as just described, and the air washed, the 

 two odours will be found to be identical, which is a pre- 

 sumptive evidence that electricity has in some way been 

 concerned in the formation of ozone an idea which ex- 

 tended experiment fully confirms. 



It has already been stated that the most prominent 

 quality of ozone is its highly developed oxidising power. 

 By taking advantage of this property, we are supplied 



1 It 



