1868.] SMALLWOOD — ON OZONE. 379 



used by me for years ; but I have since found that strips of well 

 washed calico, after dipping them in the solution and smoothing 

 their surfaces, answers better than paper ; the calico seems 

 more readily to absorb any moisture present, and also to retain 

 it better than the paper, and for experiments will be found 

 better suited for the purpose than paper slips. The exposure 

 of these tests, free from rain, but placed in the light, causes them 

 to become first a pale straw colour, increasing to the tint of a dried 

 leaf, then a deep brown or dark violet approaching to black, which 

 being wetted with pure water resolves into a blue. The decompo- 

 sition which takes place in these tests is owing to the fact that 

 the Ozone acts similarly to an acid, uniting with the potassium 

 forming potash, and a portion of the iodine is set free, which 

 unites to the starch, giving the peculiar blue colour just alluded 

 to ; the starch is only used to estimate the amount present by the 

 depth of colour, and this test is sometimes called an Ozonoscope. 

 The amount is measured from to 10, the different degrees of 

 shade indicating its amount, 10 being the deepest shade. Dr. 

 Moffatt advises that the test papers be placed free from light, but 

 having a free access to air ; I have followed both these methods, 

 and the results are nearly alike. Should there be a great 

 amount of moisture in the atmosphere, the exposed test paper 

 attains at once its blue colour, which becomes brown as it 

 dries, but the blue colour may be again attained by moisture or 

 re-wetting with water. Ozone is colourless, possessing a peculiar 

 odour, resembling chlorine, and when diluted cannot be distin- 

 guished from the electrical smell ; its density is said to be four 

 times that of oxygen; it is a most powerful oxydizing agent, con- 

 verting most of the metals into peroxides ; it is very slisjhtlv 

 absorbed by water after long contact; a very high temperature 

 destroys its properties ; it possesses bleaching qualities — hence its 

 affinity to chlorine ; it combines witlrchlorine, bromine and iodine ■ 

 it is also rapidly absorbed by albumen, fibrine, blood, and other 

 such like solutions. It is a most powerful disinfectant, and when 

 even largely diffused in atmospheric air causes difficult respiration, 

 acting powerfully on the mucous membrane, and in still larger 

 quantities may prove fatal. Its presence is easily detected in 

 the state produced in the laboratory as well as the atmosphere ; 

 its rapid production, its peculiar smell and other marked proper- 

 ties, render it somewhat less difficult to investigate than many 

 other substances. 



