214 



Ozone and the Atmosphere. 



It will be noted that potassium iodide is the most sensitive 

 test, changing rapidly while dry, using this term to apply to 

 papers having only such hygroscopic moisture as had been at- 

 tracted from the atmosphere. The thallium papers are also 

 very sensitive. But when exposed for some time, in common 

 with the other ozonoscopes, and then moistened, they fall be- 

 hind the iodo-starch papers, which occupy an intermediate po- 

 sition between them and the potassium iodide test. The iodo- 

 starch papers arrange themselves in an order corresponding 

 to the amount of potassium iodide they contain, except the 

 cadmium iodo-starch paper, which, unlike the other ozono- 

 scopes of this class, does not, on moistening, after long ex- 

 posure turn brown, but remains of a persistent blue. In some 

 trials it fell below the thallium, alizarine, and Houzeau tests in 

 sensitiveness. It is important to note that the alizarine and 

 Houzeau tests, whatever may be their other merits, are less 

 susceptible than than the potassium iodide and iodo-starch tests ; 

 and the manganese and lead sulphide are evidently inapplicable 

 as atmospheric ozonoscopes. 



Influence upon Ozonoscopes of constituents of the Atmo- 

 sphere other than ozone. 



OZONOSCOPES WITH NITEOUS FUMES (VISIBLE.) 



OZONOSCOPES. 



KI 



Cadmium 



Moffat 



Lowe 



Osann 



SchiJnbein 



Houzeau 



Alizarine (with K I) . 

 (no •' " ) 



Thallium 



Manganese Acetate 



•' Sulphate.. 



Lead Sulphide 



Guaiacum 



Brown (1) 



Lower end lilac, upper brown (2) 

 Brown (5; 



Light brown (6) 



Lilac <7) 



Lifiht brown (9) 



Red (8) 



Brown 1 

 Yellow I 

 Doubtful 

 Unaltered I 



(10) 



Bleached white 

 Dark blue 



(11) 



(4) 

 (3) 



WHEN MOISTENED BECAME. 



Bleached 

 Bluish-black 

 Dark blue 



Light blue 

 Dark blue 

 Bed 



Brown 

 Unaltered 



fl) 

 (2) 

 (3) 

 (4) 

 (6) 

 (5) 

 (8) 



(7) 



The air in the bell-jar, in which the tests affected as above 

 were suspended, contained nitrous fumes in quantity just suffi- 

 cient to give a recognizable color; in the following experi- 



