Mr. E. J. Lowe on Ozone. 231 



2. Direction of the Wind. — There is most ozone with the wind 

 between S. and S.W., and least when between N. and N.E. 



3. Protection of the test from light. — It is absolutely requisite 

 that the test should be in a dark box ; and no box has been found 

 to answer so well as that constructed by myself, and known as 

 " Lowe's Ozone box," an account of which has been furnished to the 

 Royal Society* and to the British Association. This box, if freely 

 exposed, and made to veer with the wind, so as always to present the 

 opening to the direct current, is everything that could be desired. 



The foregoing observations will be sufficient to show that precau- 

 tions are requisite in these records, and that certain corrections are 

 necessary before we can declare whether ozone is present in a certain 

 fixed amount, or whether it changes from hour to hour. These correc- 

 tions have yet to be found out ; those for the height of the barometer 

 and the force and direction of the wind will be considerable. 



Part II. 



The ozone tests heretofore used have appeared to me to be un- 

 satisfactory, and, on close examination, I found them to be faulty in 

 many respects. The paper used had a glaze upon it, which pre- 

 vented the solution from penetrating it ; substances, moreover, had 

 been used in its manufacture which acted injuriously on the tests. 

 Again, the starch of commerce was found to be impure ; it is manu- 

 factured with lime, sulphuric acid, and chlorine, substances fatal to 

 these tests. The iodide of potassium was also impure ; and there 

 has been a want of uniformity in the proportions of starch and iodide 

 of potassium employed by different observers. 



Having found out that the starch of commerce was impure, I pro- 

 cured a jar of wheat-starch in the wet state before any chemicals 

 had been used. This was steeped in distilled water, which was 

 changed every two days until quite sweet to the taste, and, although 

 by along process, a chemically pure starch was thus obtained. 



Sir John Herschel suggested trying other vegetable starches ; I 

 therefore made starch from rice, potato, sago, and wheat. 



I obtained chemically pure iodide of potassium from Mr. Squire 

 of Oxford Street, who forwarded me two samples made expressly for 

 these experiments, the one prepared with water, the other crystal- 

 lized several times from alcohol. 



On the recommendation of Dr. R. D. Thomson, 15 grains of pre- 

 pared chalk have been added to each ounce of air- dried starch to 

 prevent it from becoming sour from any moisture that might be con- 

 tained in it ; subsequent observations have proved that this is abso- 

 lutely requisite for uniformity of effect, as the intensity of action 

 depends upon the amount of water contained in the starch, which is 

 apparent from the following experiment : — 



Tests made with air- dried starch — 



a. Without further drying became coloured in 5 minutes. 



(d. After further drying by fire-heat for 1 minute became coloured 

 in 7 minutes. 



* Phil. Mag. S. 4. vol. xxi. p. 466. 



