1863.] 521 



y. After further drying by fire-heat for 3 minutes became coloured 

 in 9 minutes. 



$. After further drying by fire-heat for 10 minutes became co- 

 loured in 13 minutes. 



e. After further drying by fire-heat for 30 minutes became co- 

 loured in 20 minutes. 



r). With chalk added became coloured in 20 minutes. 



With regard to the calico or paper used for the tests, both stained 

 when impure. However, Mr. Joseph Sidebotham of the Strine 

 Works prepared for me some chemically pure calico, and I was also 

 enabled to procure a very porous chemically pure paper, both of 

 which answer perfectly. 



Having succeeded with the ozone slip tests, I tried as a first ex- 

 periment a mixture of 10 parts of starch to 1 of iodide of potassium 

 as a "dry-powder test;" this, when well mixed in a mortar, was 

 bottled ready for use. A small portion was placed in the open air, 

 and ten minutes' exposure showed that powder tests were an un- 

 doubted success, being more sensitive than the test slips. My next 

 determination was what strength would colour quickest, and accord- 

 ingly a number of strengths were prepared, varying in the propor- 

 tions from 1 of iodide of potassium and 1 of starch up to I of iodide 

 of potassium and 30 of starch, the starch used being made from 

 wheat. From these experiments it was found that the proportion of 

 1 of iodide of potassium to 5 of starch was invariably the darkest, 

 the degree of darkness diminishing in either direction when other 

 strengths were used ; thus 1 of iodide of potassium to 4| of starch, 

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



On repeating these experiments with potato-starch, the pro- 

 portion that coloured soonest was 1 to 2^ ; and this second series 

 of experiments proved that with each starch a special formula is 

 requisite. 



My next experiments were with the view of ascertaining the effect 

 of various acids and chemical substances on the ozone powder tests. 

 For this purpose I procured a number of cups for solutions, and small 

 pill-boxes to hold the powder tests, and these were placed together 

 under separate bell-glasses. The result was that the following 

 coloured the powder tests very rapidly : Hydrochloric acid, nitric 

 acid, nitrous acid, chloride of lime, phosphorus, iodine (in scales), 



