348 



NATURE 



\Mar. 5, 1874 



27 milligrammes of ozone, and in the other 9 '6 litres 

 of the same gas containing 38 milligramme? of ozone, 

 were exposed to the action of heat, so as to destroy 

 all ozone reaction?, when not a trace of water \\as ob- 

 tained ; the increase in weight of the desiccating apparatus 

 being in the first case only one-thiid, and in the second one-half, 

 of a milligramme. If Baumert's experiments had beeii correct, 

 24 milligrammes of water should have been formed in these 

 experiments. The general conclusions at v.'hich I arrivifd weie : 

 "\ii'sX. no gaseous compomid, having the composition of a per- 

 oxide of hydrogen, is formed during the: electrolysis of wafr, 

 and that ozone Jrom whate^'er source derived is one and the same 

 body, having identical properties and the same constitution, and is 

 not a compound body, but oxygen in an alteied or allotropic condi- 

 tion." ("Phil. Transactions" for 1S56, p. 13.) 



The next step in the investigation of this singular body was 

 the discovery that oxygen gas in changing into ozone diminishes 

 in volume, or becomes condensed, recovering its original volume 

 when the ozone is changed back into oxygen by the action of 

 heat or otherwise. This relation between ordinary oxygen and 

 ozone was first announced in i860 by Prof. Tait and myself in a 

 communication to the Royal Society of London. Oxygen ^as in 

 a dry and pure state was introduced into a tube sealed at une 

 end and terminating at the other in a fine tube bent as sho An 

 in Fig. I, and containing a short column of sulphuric acid. Two 

 platinum wires were hermetically sealed into the sides of the 

 wide tube, the distance of the ends mthin the tube being abjut 

 20 millimetres. 



When an electrical discharge without visible sparks was passed 

 between the extremities of the platinum wires, the sulphuric acid 

 rose in the adjacent leg of the U-tube, and from the change of 

 level the amount of the condensation, or diminution of volume, 

 which the oxygen had undergone was easily calculated. The 

 apparatus was then hermetically sealed and the reservoir heated 

 to 270° C, so as to destroy the ozone. Alter allowing the reser- 

 •voir to cool, the sealed end of the U-tube was opened, wKea the 

 original volume of the gas was foand to be restored. Strong 

 electrical sparks were found to give scarcely one-fourth of the 

 contraction which occurred with the silent discharge, and if 

 sparks were passed through the gas when fully contracted by the 

 silent discharge, the contraction was reduced to that which the 

 spark would "have produced in the original gas. In the same 

 paper it was shown that no further diminution of volume occurred 

 when the contracted gas was agitated with a solution of iodide 

 of potassium so as to absorb the ozone. A similar result was 

 obtained on agitating the contracted gas with iodine. The ozone 

 reactions in all these cases disappeared, but without any change 

 in the volume of the gas. With mercury and silver, not only was 

 theie no contraction, but expansion actually occurred, which was 

 explained on the assumption that the oxide at first formed exer- 

 cised a catalytic action on part of the ozone and restored it 

 to the state of ordinary oxygen. Similar results were obtained 

 with electrolytic ozone, 'i'hree years later these experiments on 

 the condensation of oxygen in changing into ozone, and on the 

 action of ozone upon a solution of iodide of potassmm were re- 

 peated and confirmed by Von Eabo and by \'on Babo and Claus. 

 We did not attempt to give any absolute explanation of these 

 singular facts ; but discussed them under different aspects. We 

 showed that on the allotropic view of the constitution of ozone 

 its density must be enormously great ; unless it was assumed that 

 " when ozone comes into contact with such substances as iodine, 

 or a solution of iodide of potassium, one portion of it, retaining 

 the gaseous form, is changed back into common oxygen, while 

 the remainder enters into combination, and that these are so re- 

 lated to one another that the expansion due to the former is 

 exactly t qual to the contraction arising from the latier." On 

 this assumption, which however we did not consider p.obable, 

 we remarked that " our experiments may be reconciled wiih the 

 allotropic view, and an ordinary density, but stdl one greater 

 than that of oxygen." A similar explanation of our expeiiinenis 

 but connected wiih a peculiar view of the molecular cons'.itution 

 of oxygen was proposed in 1S61 by Dr. Odling. "If we con- 

 sider," he remarks, "ozone to be a compound of ox) gen with 

 oxygen and the contraction to be consequent upon their combi- 

 nation, then if one portion of this combined or cuncentiated 

 oxygen were absorbed by the reagent, the other portiL.n would 

 be set free, and by its liberation might expand to the voiu:ne of 

 the whole ; thus, if we suppose three volumes of oxygen to be 

 condensed by their nnilual combination into two volumes, then 

 nn absorbing one-third of this rombined oxygen by mercury, the 



remaining two-thirds would be set free and consequently expand 

 to their normal bulk, or two volumes — 



- + - + + - + - 



O O O -I- Hg= = Hg=0 + O O." 



Soret, experimenting in 1866 upon the mixture of oxygen and 

 ozone obtained by electrolysis, made the important discovery, 

 that if this mixture is brought into contact with oil of turpentine, 

 or oil of cinnamon, a diminution of volume takes place, equal in 

 amount to twice the augmentation of volume which the same 

 mixture would sustain if the ozone were converted by heat into 

 ordinary oxygen. In other words the volume of ozone, measured 

 by Its absorption by the essential oil, is twice as great as the dif- 

 ference between the volume of the same ozone and oxygen. 

 Hence Soret concluded that the density of ozone is one and a half 

 times that of oxygen gas. 



The latest investigations on this subject are due to Meissner 

 and Brodie. The former has fully confirmed my early experi- 

 ments, according to which the increase in weight of an acid solu- 

 tion of iodide of potassium, when electrolytic ozone is passed 

 through it, corresponds exactly to the weight of oxygen absorbed, 

 as calculated from the liberated iodine. Meissner has also found, 

 as I had long before stated, that when a neutral solution of iodide 

 of potassium is employed, the results are variable and untrust- 

 worthy. 



Brodie has examined the action of ozone on a variety of liquids, 

 and has confirmed the results of Prof. Tait and myself that no 

 diminution of volume occurs when ozone is removed from a mix- 

 ture of ozone and oxygen by a solution of iodide of potassium. 

 With other liquids he has obtained volumetric results which he 

 considers to be definite and which differ from any previously 

 observed. I am inclined to think that they are rather complex 

 cases, involving the volumetrical changes already known in vari- 

 able proportions. His experimental results, moreover, when 

 examined in detail, do not appear to be sufficiently concordant 

 to justify the sharp conclusions he has deduced from them. 



Brodie has obtained for ozone prepared by the electrical dis- 

 charge the same density (one and a half times that of oxygen) 

 which Soret had previously obtained for ozone prepared by elec- 

 trolysis. He considers a suggestion of Prof. Tait and myself, 

 that oxygen may possibly be decomposed by the electrical dis- 

 charge, not to be supported by the facts he has observed. 



I will now give a brief statement of the methods of preparing 

 ozone and of its leading properties. 



Ozone may be obtained by the action of the electrical spark, 

 or the glow or silent discharge on pure oxygen. Wiih the 

 silent discharge, as has been before stated, at least four times as 

 large an amcunt of ozone is obtained as with the spark. As re- 

 gards the actual amount of oxygen which, under the most favour- 

 able conditions can be converted into ozone, the highest recorded 

 result was obtained in an experiment by Prof. Tait and myself, 

 in which a contraction of one-twelfth of the origin.al volume of 

 the oxygen, or 8 '3 per cent., occurred ; but we were unable in 

 other trials to produce again so great a diminution of volume. 

 The greatest contraction attained in the experiments of Von 

 Babo and Claus amounted to 574, and in those of Brodie to 

 6 '52 per cent. The doubt which existed as to the accuracy of 

 our solitary experiment I have lately been able to remove, and 

 by a slight modification in the form of the apparatus I have 

 succeeded in obtaining greater contractions than any hitherto re- 

 corded. In one of the first trials the diminution of volume 

 amounted to more than 10 per cent, and there can be little 

 doubt that with care even greater contractions than this may be 

 attained. 



As the method referred to enables the contraction of oxygen 

 in changing into ozone to be exhibited as a class experiment, I 

 will describe it in some detail. The excellent induction tube of 

 .Siemens, in which the electrical discharge Irom an induction coil 

 acts upon air or oxygen, as it flows between two thin tubes of 

 glass, whose surfaces are at a distance of a few millimetres from 

 one another, has hitherto been employed to obtain a continuous 

 stream of ozone in a more or less concentrated state. But this 

 apparatus can easily be modified so as to show the contrac- 

 tion which takes place when oxygen is converted into ozone. 

 Fig. 2 exhibits the modification I have given for this purpose 

 to the ordinary form of .Siemens' tube. At c it terminates in a 

 capillary tube, the end of which is hermetically sealed, after a 

 stream of pure and dry oxygen gas has been passed through the 

 apparatus for a .sufficient lime to displace the air. In exact 

 experiments the otlier end (/' ) is at the same time sealed and after- 

 wards opened under sulphuric ncid. For class puijioscs it will 



