Ozone and the Atmosphere. 211 



a concentrated, others in a more dilute solution, but the results 

 obtained with each were identical. 



Similar remarks apply to the plumbic sulphide papers, which 

 were so prepared that each square centimeter of surface 

 contained about 10 mgrms. of the sulphide. They were not 

 sensitive. Moreover, in an atmosphere of hydrogen peroxide 

 or nitrons acid, they were bleached. 



Y. Those depending upon the oxidation of organic bodies, 

 with the development of a characteristic change of color. 



The only one of these substances particularly studied, was 

 the resin of Guaiacum. It appeared essential to use this resin 

 in the original masses, for if that which had been pulver- 

 ized was used, even if it had not been exposed to light, the 

 tincture made from it appeared deficient in sensitiveness. A 

 tincture containing 8 p. c. of the resin was prepared with 90 

 p. c. alcohol. The papers so prepared had a slight yellow 

 tinge. They were moderately sensitive, acquiring speedily 

 when dry a faint blue color, and when moistened, occupying a 

 position midway between the ozonoscopes most sensitive, and 

 those least so, to the influence of ozone. They were rapidly 

 turned greenish-blue by nitrous acid, and bluish-green by 

 hydrogen peroxide. For these reasons, and on acconnt of 

 their deficient sensibility, they are objectionable as atmospheric 

 ozonoscopes.* 

 * Examination of Ozonoscopes under known conditions. 

 Having prepared pure materials, the following ozoaoscopes 

 were made, care being exercised to render them as nearly sim- 

 ilar and uniform as the nature of the tests would permit. They 

 were preserved in tightly-stoppered bottles, in the dark, and 

 entirely removed from the laboratory odors. The potassium 

 iodide papers were made with a solution containing 15 grms. 

 of the salt. The proportion of iodide of potassium and starch 

 in the iodo starch papers, is that recommended by the observers 

 whose names they bear. The amount of water is the same in 

 all, in order that the papers compared may be as nearly simi- 

 lar as possible. 



* It is probable that the influence of light, as well, would be unfavorable to the employ- 

 ment of organic matters as ozonoscopes. 



