Mar. 12, 1874] 



NA TURE 



365 



of oxyt'en containing not more than ^Jjth part of ozone will alter 

 wholly the physical characers of several pounds of mercury, 

 taking away ihe lustre and convexity of the metallic surface 

 and causing the mercury to form an adhering mirror to the 

 surface of the glass vessel in whicli it ii contained. If owjne in 

 a diluted state is slowly passed through a tube filled with silver 

 leaf, the metal will \>e oxidised to the distance of 2 or 3 milli- 

 metres, but the oxidation will not proceed further, although the 

 ozone reactions are wholly destroyed. This striking result is due 

 to the catalytic action of the portions of oxide which are first 

 formed. .So small is the amount of oxide pnxluced in this case 

 that, in a glass tube through which many litres of electrolytic 

 ozone had been passc'l, the increase In weight from the formation 

 of oxide only amounted to a scarcely appreciable fraction of a 

 milligramme. 



Oz<^)ne Is absorbed by oil of turpentine, oil of lemon, and other 

 essential oils. These oils have also, like phosphorus, the power 

 of changing oxygen into ozone, while they arc slowly oxidising ; 

 so that if oil of turpentine is shaken for some time in a flask 

 filled with air or oxygen, the oil will acquire ozfjne properties. 



Ozone decomposes a solution of iodide of potassium, liberating 

 the iodine, which may be discovered by its red colour, or its blue 

 compound with starch. If the action is continued sufficiently 

 long, the free iodine disappears from the formation of iodate of 

 pota.ssium and the solution becomes colourless. Reddened litmus 

 paper moistened with a solution of iwlide of potassium is turned 

 blue, when expcrsed to the action of ozone, in consequence of the 

 caustic alkali formed by the decomposition of the salt. In em- 

 ploying this test it will often be found advantageous to remove 

 the free iodine by washing the paper with strong alcohol. This 

 form of the iodide of potassium lest has been proposed by Houzeau 

 for the discovery of ozone in the atmosphere. Ozone produces 

 other reactions of a similar character which it will be sufficient 

 here barely to mention. Paper moistened with sulphate of man- 

 ganese becomes brown when exposed to this agent from the for- 

 mation of the hydrated peroxide. Solutions of thallous oxide 

 are in like manner converted into the brown peroxide ; the black 

 sulphide of lead into the white sulphate, and the yellow ferro- 

 cyanide of potassium into the red salt. The action of ozone on 

 tincture of guaiacum, which it turns blue, was made a subject of 

 special study by Schonbein. 



The bleaching properties of ozone are highly characteristic 



an'l have attracted a great deal of attention. It deprives indigo 



•'. its blue colour, converting it into isatin, and bleaches 



lily litmus and other vegetable colouring matters. Attempts 



■ e been made to apply this property of ozone in the arts, and 

 , uflicularly to the refining of sugar and the bleaching of linen. 

 It has been even stated that these and other applications of ozone, 

 as a decolorizing or bleaching agent, have been successful ; but 

 the results of my inquiries on this point have, I regret to say, 

 been unfavourable, and it remains yet to \>t seen whether this 

 singular body can be marie subservient to the useful purposes of 

 life. For the preparation ot ozone on the large scale from 

 ordinary air, a moaification of the tube-generator of .Siemens has 

 been proposed by Beanes, and is an efficient and powerful in- 

 strument. 



I will not detain the Society by an account of the history or 

 properties of the problematical body to which Schonbein gave 

 the name of antozone. He considered this body to be oxygen 

 possessing permanently positive properties, while ozone itself he 

 regarded as negative oxygen. Ordinary or inactive oxygen, 

 according to him, Is formed by the union of ozone and antozone. 

 These views have not been supported by recent investigations, 

 which leave little doubt that the antozone of Schonbein is 

 identical with the peroxide of hydrogen of Tht'nard. From 

 ozone the peroxide of hydrogen can be readily distinguished by 

 the solubility of the latter in water. 



Soon alter the discovery of ozone, Schonbein having observed 

 that the air of the country frequently coloured a delicate ozone 

 test-paper in the same manner as ozone itself, inferred that 

 ozone is a normal constituent of our atmosphere. He conclufled 

 that the amount of this body present in the air is different in 

 different localities, and in the same locality at different times, 

 and with great boldness he attempted to connect its presence or 

 absence wiih the prevalence or rarity of certain catarrhal aflec- 

 tions. A new field for inve^tiga'ion wms thus< pene*! up, which 

 has been a-si'luously culiivated by a la'ge and zealous bai d of 

 observers. Bcioic referring howev-r to their labours, it wdl be 

 necessary briefly to allude to the present slate of our knowledge 

 regarding the existence of ozone in the atmosphere. 



Schonbein always maintained that ozone is a constituent of 

 atmospheric air, and his various papers on this subject alone 

 would, if collcctefl, fill a large volume. In his last memoir he 

 obsenres that the active suljslance in the air acts in a f/arallel 

 manner on iodide of potassium and sub-oxide of thallium papers, 

 although more slowly on the latter; and that the thallium 

 paper, which has been colourerl brown by the air, behaves to- 

 wards reagents in the same manner as that which has been ex- 

 posal to artificial owjne. irom these facts he infers that the 

 active substance in the air is neither peroxide of nitrogen nor 

 sulphurc-ttcl hydrogen. He further states that the atmosphere 

 never contains free nitric acid, although nitrate of ammonium in 

 small quantities is frequently present ; and that neither chlorine 

 nor bromine can be present in the free state in air, on account of 

 their affinity for hydrf»gcn. Houzeau also maintained that the 

 existence of ozone in the air was proved by the alkaline reaction 

 of itjdide of potassium reaper, which had been decomposed by 

 exposure to the atmosphere. Although experiments and argu- 

 ments of this kind were sufficient to give probability to the view 

 that the active sul«tance in the atmosphere which proluces these 

 reactions is ozone, they were at the same time far from conclu- 

 sive, and some of the ablest chemists of Europe accordingly 

 considered the question doubtful, while others attributed tlie 

 effects observed to the presence of oxidising agents altogether 

 different from ozone. I will only cite on this point the opinion 

 of M. Frc'my, whose researches in conjunction with M. Becjuerel 

 on ozone have already been referrerl to. '* Without denying," 

 he remarkerl at a meeting of the Academy of Sciences in 1865, 

 " the importance of the indications given by the paper of M. 

 Schonbein, or by that of M. Houzeau, I do not find that these 

 react irjns demonstrate with sufficient certainty the existence ol 

 atmospheric ozone. I am of opinion that the presence of ozone 

 in the air most be established anew by incontestable experi- 

 ments " 



In 1867 I made a set of experiments which I had contem- 

 plated some years before for the purpose, if possible, of finally 

 settling this important question. The method I proposed was 

 to a.scertain whether, in addition to the power of decomposing 

 solutions of iodide of potassium and of certain other salts, the 

 active body in the atmosphere possessed the other properties of 

 ozone, some of which are highly distinctive. The inquiry was a 

 delicate one, in consequence of the very minute quantity of the 

 active body which Is present, even under the most favourable 

 conditions, in atmospheric air. The results of this investigation 

 are given in a short note which was published in the " Proceed- 

 ings of the Royal Society " for 1867. (1) By passing a stream 

 of atmospheric air, which gave the usual reaction witli 

 icxlide of potassium paper, for some hours over the sur- 

 face of mercury in a U-tube, the metal was distinctly oxiilised. 

 (2. ) The ozone reactions disappeared when the air was passed 

 through a tube containing pellets of dry oxide of manganese. 

 The experiment was continued till 80 litres of air had traversed 

 the manganese tube without producing the slightest discolora- 

 tion of a delicate test-paper. (3.) But the crucial experiment 

 was to ascertain whether the active body in the air loses i's cha- 

 racteristic properties, or is destroyed, at the same temperature 

 (237" C.) as ozone. To determine this point, a stream of atmo- 

 spheric air, which gave strong ozone reactions, was passed through 

 a globular glass vessel (Fig. 5), covered with wire gauze, of 5 litres 

 capacity, and afterwards through a U-tube I metre in length, 

 whose sides were moistened internally with water, while the tub; 

 itself was kept cool by being immersed in a vessel of cold water. 

 After traversing the globular vessel and the moistened U-tabc, 

 the air was blown over a slip of delicate test-paper, in order to 

 ascertain the presence or absence of ozone. When the atmo- 

 spheric air was drawn through this apparatus at a uniform rate 

 by means of an aspirator raisefl by clockwork, the iodide of 

 potassium paper was dlslinctly reddened in two or three minute?, 

 provided no heat was applied to the glass globe. But on heating 

 the air as it passed through the globe, to a temperature of about 

 26^)° C, not the slightest action was produced on the paper, 

 however long the current of air continued to pass. On the other 

 hand, when air free from ozone, but containing traces of chio: ine or 

 of the higher oxides of nitrogen, was drawn through the appara- 

 tus, the test-papers were eq'ially affeced, whether the glob; v.a* 

 heated or not. The>e experiments have since been succcoafully 

 repeated by Dr. C. Fox. 



The identity of the active Ijody in the atmosphere with cz^me 

 we may now assume to be established beyond dispute, and ihe 

 accuracy of Schonbein's views on this subject to be fully con- 



