WHEN preparing my lecture on ozone during t'he recent term it seemed advisable to ascertain if this body is really produced during the slow oxidation of phosphorus in moist air as some doubts have lately becn thrown on its formation by this process. The experiments extended to an unforeseen length and i t may be well to give a short account of them although it is necessary to apologise for bringing merely quali-tative experiments under the notice of the Society. The active substance formed during the slow oxidation of phospho-rus is probably either ozone or peroxide of hydrogen ; the direction the experiments took therefore was to decide which of these bodies was present in the air in which phosphorus was nndergoing oxidation. It is well known that hydroxyl is readily destroyed by alkalis by a solution of chromic acid and by a solution of an alkaline permangsn-ate while ozone is unaffected by a solutiori of sodic carbonate and by chromic acid and appears to be only slightly attacked by the alkaline permanganate.Ozonised oxygen prepared by passing dried oxygen through a Sie-mens tube of the form employed by Sir Benjamin Brodie (Phil. Tyarzs., 18'72 162 438) was passed through a U-tube 9; inches long filled with glass and containing in succession sodium carbonate solution (previously saturated with carbonic anhydride to remove any possible trace of free alkali) a mixture of potassium dichromate and sulphuric acid and potassium permanganate previously saturated with carbonic anhydride. I n all these cases the ozone passed through even when the U-tube was surrounded with boiling water.Hydroxyl on the contrary is readily decomposed by a solution of sodic carbonate especially a t the temperature of boiling watw a mixture of hydroxyl and sodium carbonate effervescing powerfully when a test-tube containing it is plunged in boiling water ; it imme-diately transforms chromic into perchromic acid a t the common tempe-rature and when it is mixed with potassium permanganate oxygen is rapidly evolved. Corresponding experiments were made with tlie air in which phos-phorus was slowly oxidising. A wide cylinder was covered by a 1oose:y fitting perforated glass plate through which a glass tube reaching nearly to the bottom of the cylinder was passed. A stick of phos-phorus lay horizontally a t the bottom of the cylinder a i d was partl McLEEOD OX T1IE FORMATION O F OZONE ICTC.11!) immersed in water. The air was drawn through the U-tube previously mentioned and then into a flask containing a solution of potassic iodide and starch in all cases the solution became blue both wlien the U-tube containing the reagents was cold and heated to 100". It was possible that the gas did not cDme intimately in contact with the reagents in the U-tube filled with broken glass; another tube, l 2 i inches long was therefore constructed and filled with very small pieces of pumice-stone tightly packed. The pumice-stone was satu rated with solution of soclic carbonate ; in this case also the active gas passed. It seemed desirable that the effect of heat shonld be tried on the gas.For this purpose an apparatus was constructed consisting of a large U-tube ccntnining pumice-stone and sulphuric acid a narrow U-tube which could be heated in a test-tube a weighed tube containing pumice-stone and sulphuric acid and a flask with a solution of potassium iodide and starch acidified by sulphuric acid. Some of the joints were made as suggested by Brodie by slipping a wide tube over the ends of the sepa-rate parts of the apparatus and filling the annular space with melted paraffin; those on each side of the tube to be weighed consisted of wide tubes fitted with corks through which the narrow tubes passed, and in order to prevent to some extent the action of the corks on the gas a tube a very little larger than the narrow ones was slipped over the ends.Quantities of the gas from the phosphorus cylinder varying between 1 litre and 5 litres were drawn slowly (at the rate of about a litre an hour) through the apparatus. In some cases the narrow U-tube was left a t the ordinary temperature sometimes plunged in boiling water and sometimes in melted paratlin at temperatures of 1.50" and 200". The U-tube was weighed before and after each ex-periment; and the blue solution obtained by the act'ion of the gas on the potassium iodide and starch was at the end of each experiment decolorised by a decinormal solution of sodium thiosulphate. There was very little regularity in the results and it appeared as if the increase of weight of the second sulphuric acid tube was due to the escape of some of the phosphorous acid through the fimt tube and with the forma-tion of water.That some of the phosphorous acid did pass through the first tube was shown Ly a slight white ring which formed inside the narrow U-tube a t the level of the melted paraffin. The maximum in-crease of weight in twenty-four experiments T T ~ S -0035 gram t h i s took place in an experiment in which the small U-tube was cold and in this case the quantity of solution of sodium thiosulphate employed to decolorise the solution was 3.65 C.C. As the formation of active gas by the phosphorus is by no means regular it would be impossible to com-pare the results with one another ; but four consecutive experimeiits although not inadc on the same day gave the following numbers : 120 NCLEOD OK THE FORMATION OF OZONE ETC.Quantity of thiosulphate solution required to Increase of weight Bas Temperature of sulphuric acid decolorise blue aspirated. of U-tube. tube. liquid. 4690 C.C. cold -0026 gram 2.55 C.C. 2760 , 100" *0008 , 1.9 >, 4600 , 130" *0026 , 3.2 ,, 2760 , 200" -0006 , 1.8 9 , Now as 1 C.C. of the sollition of the thiosulphate corresponds to -017 gram of hydroxyl which on decomposition by heat would form -009 gram of water and as we may reasonably assume that at 200°, at least one-half of any hydroxyl that might be present would be decomposed we should in the last experiment expect an increase of about *016 gram in the sulphuric acid tube instead of only -0006. Hydroxyl is known to combine with acids and i t may therefore be expected that strong sulphuric acid would absorb i t to see if the gas from phosphorus was rendered inactive by contact with sulphuric acid, a bulb of about 200 C.C.capacity was blown on a tube and some of the air from the phosphorus cylinder drawn into it. One end of the tube was now sealed and the other dipped into sulphuric acid and the hulb warmed to expel some of the gas; on cooling the acid entered the bulb which was then turned round so as to moisten the sides. The bulb was left in this condition for four days being occasionally shaken so as to renew the surface of the acid. The point was then cut off and the gas drawn through potassic iodide and starch which was im-mediately rendered blue. It may be thought that hydroxyl and ozone are simultaneously pro-duced during the oxidation of phosphorus ; but this is hardly possible, for the bodies mutually decompose one another under certain condi-tions.To examine the action of these substances on one another some commercial peroxide of hydrogen was introduced into a cylinder of ozonised oxygen and to my surprise the gas in the cylinder affected ozone paper even after prolonged agitation. If however the small quantity of acid mixed with the hydroxyl is neutralised with sodium carbonate o r the liquid made very slightly alkaline the ozone is destroyed in a few minutes. During the oxidation of phosphorus an acid is of course formed and this may prevent the mutual action of the ozone on the peroxide although it seems hardly probable. The above experiments seem to show that the gas obtained during the slow oxidation of phosphorus possesses the properties of ozone, and not the properties of the only known peroxide of hydrogen; whether any other product is formed remains to be proved