164 Ozone and Ozone Tests. 



potassium, and Moffat another of 2\ starch to 1 of iodide of 

 potassium. No satisfactory reason was given why Moffat used 

 so different a formula to Schonbein. It occurred to me that, if 

 a number of different strengths were prepared from equal 

 portions of each up to 30 parts of starch to 1 of iodide of 

 potassium, that if one of these strengths was coloured sooner 

 than another this should be the proper formula to adopt. 



Having mixed a number of powders of different strengths 

 with wheat starch, and exposed them to the air, a very short 

 exposure showed that 1 part of iodide of potassium to 5 of 

 starch was soonest coloured, and gradually darkened beyond 

 all other strengths ; and many repetitions of these experiments 

 always gave the same results. The degree of darkness di- 

 minished in either direction when other strengths were used — 

 thus, even 1 of iodide of potassium to 4| of starch, or 1 to 

 5|, were neither so dark as with a strength of 1 to 5. It 

 became, therefore, evident that these were the proper propor- 

 tions to be used with wheat starch ; or, at all events, with per- 

 fectly pure wheat starch, such as I had experimented upon. 

 On repeating these experiments with potato starch, the propor- 

 tion which coloured soonest was 1 to 2 £ of starch, showing that 

 the formula must be based on actual experiment, and that a 

 special formula is requisite for each vegetable starch. It next 

 became a question as to what starch would be most sensitive • 

 and, to arrive at this, experiments were tried with tulips, crocus 

 narcissus, snowdrop, arum, etc.; and very fine starch was manu- 

 factured from the bulbs of all these plants. Investigations, 

 which I am at the present moment engaged in, will soon show 

 what starch will be the best to adopt. 



Further experiments were tried, with the view of determining 

 the effect of various acids, etc., on the ozone tests ; and in order 

 to ascertain this conclusively, two small cups were placed under 

 a bell-glass — one containing an acid or other substance, and 

 the other an ozone test powder. From these it was found that 

 hydrochloric acid, nitric acid, nitrous acid, chloride of lime, 

 phosphorus, iodine in scales, iodine dissolved in alcohol, carbo- 

 nate of lime, and carbonate of iron, on which an acid had been 

 ] mii i red, all coloured the tests, and some most rapidly. These 

 experiments also showed that a new method of investigating 

 ozone had becomo apparent; it was found that a different 

 colour was imparted to the powder, and that the powder pene- 

 trated more or less deeply, accordingto what coloured the test; 

 differences of effect took place, by which tho different materials 

 used might be recognized. Iodine, although it coloured to a 

 brown-black, was merely a surface colouring, below which tho 

 powder was colourless ; PhosphoBUS, a bluish-black, on the sur- 

 face only ; Chloride op Lime, deep brown, on the surface only 



