February 22, 19 12] 



NATURE 



DO 



THE IXDLSTRIAL USES OF OZONE. 

 T^HE production of ozone by the discharge of a 

 ■*■ frictional electrical machine was originally 

 noticed by Van Marum in 1785, but it was Schonbein 

 in 1840 who first actually prepared it and gave it the 

 name of "ozone," from the Greek oCav, meaning 

 smell. He also showed that it was much more active 

 as an oxidising agent than ordinary oxygen. As is 

 well known, it is produced by the slow oxidation of 

 phosphorus, and the peculiar odour of this element is 

 really not the odour of phosphorus, but the odour of 

 ozone, and this can be shown to be the case by adding 

 small quantities of substances to phosphorus, which 

 prevent its oxidation, when the odour is no longer 

 perceptible. It also appears to be produced in small 

 quantities by the burning of hydrocarbons. It is like- 

 wise formed in the open country, partly by evapora- 

 tion, but probably most largely by the action of ultra- 

 violet rays from the sun. This at any rate would 

 account for its formation in the higher regions 

 of the atmosphere. It is formed in con- 

 siderable quantities when fluorine acts upon 

 water. If a drop of water is introduced into 

 a tube filled with fluorine, reaction imme- 

 diately ensues, and the tube becomes filled 

 with deep blue vapour. This is ozone which 

 has a blue colour when concentrated. 



Ozone is also produced at the anode when 

 acid solutions of water are electrolysed, par- 

 ticularly if the electrode is a platinum tube 

 through which cold water is passed. By 

 this means Fischer and Massenez have ob- 

 tained oxygen containing 25'27 per cent, of 

 ozone in electrolytic oxygen by electrolysing 

 at 0°. Such a process would not, however, 

 be satisfactory on a large scale, owing to 

 the cost of production. It is also produced 

 by heating and suddenly cooling oxygen, 

 and also by the action of the ultra-violet 

 rays, produced by the mercury-vapour lamp. 

 The only method employed commercially to 

 prepare it is to subject oxygen to the 

 action of the silent electric discharge, the 

 oxygen thereb}^ receiving electrical energy 

 and becoming converted into ozone thus : — 



3O2 + energy = 20.3. 



As the formation of ozone is an endo- 

 thermic reaction it follows that it is less 

 stable than oxygen, and is in a condition 

 in which it will readily part with the energy 

 originally received electrically in the form 

 of heat — e.g. when the pure gas explodes, 

 or as chemical energy when it acts as an oxidising 

 agent. The thermochemical equation accdiiiits for iis 

 instability : — 



02 + = 03 — 32,400 cal. 



It is only within the last decade that the 

 employment of ozone for the purification of 

 water has been practically worked out and 

 actually employed commercially. \;iiiciii- pro- 

 cesses have been suggested and einploycd tor the 

 sterilising of water, and it will perhaps be as well 

 In the first place to refer to the different forms of 

 construction of the apparatus. All the api),ir;itiis 

 employed depends upon some method or otlit r of 

 obtaining a silent electric discharge; consequently very 

 bigh eleclrical potential is necessary. In general the 

 "lit discharge takes place between conducting plates 

 I rated by means of a dielectric. The original 

 o/uiiiser of this t\i)c w.ts the invention of W. von 

 ■Siemens, and consisted of two concentric tubes, which 

 '^rf' coated on their outside surfaces with tinfoil, the 



NO. 2208, VOL. 88] 



glass of the tubes acting as the dielectric. Berthelot 

 used glass as the dielectric and a liquid as the con- 

 ductmg material. Modifications of both these forms 

 are used commercially. The " Ozonair " apparatus con- 

 sists of wire gauze as the conductor, separated by 

 mica as dielectric. The ozoniser is enclosed in an 

 iron case when the ozone is to be produced for water 

 sterilising or similar purposes. When it is required 

 for the purification of the air or for ventilation it is 

 open and the air is drawn through the apjiaraius and 

 distributed by means of a fan. Fig. i sho\y> a semi- 

 enclosed type in wliich the grid can be entiielv en- 

 closed by completely boxing in. The electrical tension 

 employed is about 7000 volts. 



The Siemens-Halske type which is used for water 

 sterilising is illustrated in I"ig. 2. It consists of con- 

 centric pipes p and K pl.ued one within the other; 

 the inner one is (>: .iluininiuin, and is connected \vit!i 

 the leads carrying rt hii^h-iension current inarked in 

 the diagram as +, as this is ihr jiositiye pule. Ilie 



Fk; 



glass cylinder E is the other pole; it is surrounded 

 with water which can be cirrulati-d f(ir cooling pur- 

 poses, and as thi-- i- "alixe" ii i.eeixes iis charge 

 from it. Tfie \s.iler uhich -^mmundv the gl.-KS 

 cylinder I'eceixe's it- eleetrieiiv lumi ihe iron-coiU.iin- 

 ing box, which !■- eartln'tl, and cunsei|U' m U t.nni- iln> 

 negative pole. I lie annular space l'ei\' 1 I K 



is where the sileiii discharge takes |il.i( i eoni- 



plete apparatus consisis ol .1 east-ii(in lui\ tiixided 

 into three chainliiis, th.- 1m\m 1 < ii nnhiT lor teeeiving 

 and conveyin)^ th'- air to th.' (..one iul.es, .m lieinietic- 

 ally sealed middle ( niii|iartineni into wliieli th-' o/one 

 tubes .'U-e illserN d 1)V nieaiis ..f .1 -lull l.illd. 



and an uppei' i ■'inpai-imeiu tor rolliciin. :iis.(| 



air. An aliern.niiiL^ riniem at S( m .0 \m1u 1- emplovt'd. 

 A verv lii^li I'Mision .ippai.iiiis is ih,' Abraham 

 Marmier, in wliieli ,i potential ot 40, (...o \-olfs is 

 employed. I' is in.tdi' up ol a nmnliei ol hiilldw 

 cylindrical clectrodi's, uiiieh if insulat.d In means 

 of glass and contained in ,1 lio\. I"r 1 ciolinu; purposes 

 water is circulated throuL;li tlie . l.ctiodi"-. 



