1122 



METEOROLOGY. 



[PROPCCTIOS OF OZONB. 



with an easy method of recognising it, by means of a test- 

 paper, imbued with a mixture of iodide of potassium and 

 Urch. The chemical reader need not be informed that 

 iodine colours starch blue, whereat iodide of potassium 

 does not; therefore test-paper, containing iodide of 

 potassium and utarch, may occasionally be resorted to for 

 indicating the presence of certain bodies, which have the 

 faculty o? decomposing iodide of potassium, and liberat- 

 ing free iodine. Ozone is one of these ; which fact 

 remembered, will render the following experiment intelli- 

 gible : If a piece of this paper be held between the 

 prime conductor of an electrical machine and the 

 Knuckle, or a metallic boll, and electrical sparks trans- 

 mitted through it, spots of blue discoloration will be 

 seen on it, corresponding to each electrical spark. 



The method of detecting the presence of atmospheric 

 ozone is now readily indicated. K a strip of prepared 

 paper turn blue, the existence of ozone is demonstrated. 

 The experiment is very striking when performed near 

 the sea. During the prevalence of a land wind, the 

 tent-paper will generally afford slight indications, or none 

 at all ; during the prevalence of a sea wind, however, 

 ozone can generally be detected. 



The reader will now be prepared to form some idea of 

 the natural causes which may generate ozone. We need 

 assume no other agency than that of electricity, to be 

 assured that the production of ozone must be universal, 

 and, looking ou the world as an aggregate, continuous ; 

 and when we consider the potent nature of ozone, the 

 irritation it produces when breathed, the facility with 

 which it bleaches, corrodes, and destroys, we shall not be 

 at a loss to understand that the consequences to living 

 beings, of its excess or diminution, must be all-important. 

 A most important function of ozone has yet to be indi- 

 cated : it removes, almost more rapidly than chlorine 

 itself, the bad odours resulting from the decomposition 

 of animal or vegetable bodies. If a piece of putrid flesh 

 be immersed for a few minutes in a bottle of ozonised 

 air, the odour of decomposition is totally destroyed. 

 With these facts before us, we may form some idea to 

 ourselves of the important functions which ozone is 

 designed to accomplish. Lessen the amount of atmo- 

 spheric ozone, lower it below given limits, and increase 

 the atmospheric temperature to the degree most conge- 

 nial to organic decomposition, and the air will soon be 

 charged with disease-bearing and putrid odours. It is 

 in accordance with all that philosophy has been able to 

 teach us, in relation to the laws of epidemic and endemic 

 maladies, that the presence of such gaseous odours of 

 organic decomposition as are here assumed, must be the 

 fruitful source of disease ; and it is not possible, after 

 having studied the qualities of ozone, to refuse assent to 

 the proposition, that the existence of this agent, in com- 

 petent amount, must be followed by the destruction of 

 the pestiferous odours of organic decomposition. If, 

 however, ozone be naturally formed at any time in 

 excessive amount, it is not difficult to foresee that other 

 serious consequences must result to animal life. The 

 inhalation of an irritating gas cannot but produce in- 

 jurious effects on organs so delicate as the lungs ; and, 

 perhaps, many of the now anomalous and inexplicable 

 effects of change of air, to patients suffering from chest 

 didfinnna, may hereafter receive their solution in a more 

 intimate acquaintance with the laws of ozone. 



I'IIVKICAL PROPERTIBS or GASEOUS BODIES. The 

 word gat is of German origin, and was first employed by 

 Van Hclmont, to signify the vapour which escaped from 

 liquids undergoing vinous fermentation. At later periods, 

 the term was applied to designate every invisible sub- 

 stance disengaged from bodies by the application of fire. 

 Maoquer, a celebrated French chemist of the eighteenth 

 century, extended the meaning of the term gas to signify 

 every kind of air besides atmospheric air ; aud modern 

 chemist* have extended the meaning of the term still 

 further, t<> indicate elastic fluids, whatever their colour 

 may be, which are not readily condensible. At one time 

 it was erroneously imagined that gases did not admit of 

 condensation : in accordance with this belief, a gas was 

 defined a* being a permanently elastic fluid, thus distin- 



guishing this class of bodies from mere vapours, which, 

 so far from being permanently elastic, are very readily 

 condensible. Modern discovery has proved this distinc- 

 tion to be untenable. All the known gases, except 

 oxygen, nitrogen, hydrogen, nitric oxide, carbonic oxide, 

 and coal gas, have been liquefied, and a great number of 

 them solidified, by subjecting them to extreme cold and 

 pressure. 



Law of Marriotte The Volumes of Gates an inversely 

 to the Pressure applied. This is a very celebrated law, 

 and one that intimately concerns the meteorologist ; it 

 may be otherwise termed the law of compressibility of 

 elastic fluids. 



It will be recognised that the law in question, accord- 

 ing to the exposition of it just given, is a general law, 

 applying to a vast number of gaseous and vaporous 

 bodies. For a long time its absolute truth remained un- 

 questioned ; but, more recently, M. Regnault and others 

 have demonstrated it to be not of such universality. 



Even atmospheric air and nitrogen do not rigorously 

 conform to the law ; and carbonic acid, and liqiiefiablo 

 gases generally, are so little amenable to the law, that, 

 as applied to them, it cannot be regarded as approxi- 

 mately correct. Even the rate of compressibility of 

 hydrogen is not strictly accordant with the law, although 

 the deviation in this case is in the opposite direction to 

 the deviation when atmospheric air is concerned ; for it 

 suffers less compression than, according to the law, 

 should take place. Carbonic acid and nitrogen, com- 

 pressed -by a force of forty-five atmospheres, only lill 

 seven-tenths of the space they ought to occupy according 

 to the law. 



Now, inasmuch as the philosophy of estimating the 

 height of mountains barometrically, is intimately associ- 

 ated with the law of Marriotte, it is well to indicate that 

 this law is not quite correct ; nevertheless, as re:.' 

 atmospheric air, it is so nearly correct that we may accept 

 it without demur. 



The experiment by which the law of Marriotte was 

 deduced ia as follows : Into a strong glass tul> 

 equal diameter throughout, bent on itself 

 (as represented in Fig. 2), open at the long, 

 aud closed at the short extremity, a little 

 mercury is poured, in such a manner that it 

 shall be perfectly level in the two legs, as 

 represented by the line A B. Under these 

 circumstances, it will be evident that the air 

 inclosed between B C aud A D will be 

 equally compressed. Let us assume the 

 amount of compression to be represented 

 by the weight x. Let us furthermore 

 assume that the weight of a column of 

 mercury between O and D to be = x, and 

 let us call it m. If, then, on filling the 

 long arm of the syphon with mercury, the 

 column of air originally extending from 

 B to C be diminished to the column extend- 

 ing from B' to C, that is to say, to one-half, 

 then we have x + "* = i B C, or 



2 x = i B C ; 



proving that the compression of air within 

 the limits of the experiment is inversely to 

 the pressure applied. In like manner, 

 when the pressure is triple, the volume of 

 gas is reduced to one-third ; whon quad- 

 ruple, to one-fourth, <tc. M. Arago has 

 experimentally determined that the law rigorously a; 

 to atmospheric air up to a pressure of twenty-seven 



^pheres,* 



The Aimospliere at a Ponderable Agent. Owing to tho 

 equality of pressure which the atmosphere exercises on 

 every side, we are not ordinarily conscious of its possess- 

 ing weight. Nevertheless, its weight is no less definite, 

 under proper limitations of demonstration, than the 

 weight of any solid or liquid. The weight of the atmo- 

 sphere may be contemplated uuder two conditions : 



The etadent wilt find a more extended mathematical inve-tiirfttion of 

 thin and the following lubjccl* In tbe Section on I'urumatict, p. 769, el irq. 

 ED. 



Kig. 



B 



d 



A 



