8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 63 



discovery of important sources of error has destroyed the value of 

 observations made in this manner. Other substances in the air 

 have been found to act as reducing agents ; secondly, the color after 

 having appeared may be altered or destroyed by substances, such as 

 sulphurous acid and many organic substances. Again, the test acts 

 only in a moist atmosphere and, besides that, varies in intensity 

 according to the amount of the wind, so that, in a way, it is a 

 measure of humidity and of wind. 



A more recent test, mentioned by Huggard as more sensitive, 

 depends upon the use of what is known as tetra-paper, but is also 

 considered uncertain. The full name of this reagent is tetramethyl- 

 paraphenylendiamin paper. Notwithstanding the unsatisfactory na- 

 ture of these tests, the conclusion seems to be accepted that ozone is 

 more abundant in May and June and least abundant in December 

 and January ; more abundant in the forests and the seashore and in 

 mid-ocean and least abundant in towns where it commonly cannot be 

 detected. The following quotation is from page 332 et seq. of Vol. 

 I, Watts' Dictionary of Chemistry: 



Very little is known respecting the proportion of ozone in the atmosphere, 

 or of the circumstances which influence its production. The ozonometnc 

 methods hitherto devised are incapable of affording accurate quantitative 

 estimations. Air over marshes or in places infested by malaria contains little 

 or no ozone. No ozone can be detected in towns or in inhabited houses. 



Houzeau determines the relative amount of ozone in the air by exposing 

 strips of red litmus paper dipped to half their length in a i per cent solution 

 of potassium iodide. The paper in contact with ozone acquires a blue color 

 from the action of the liberated potash upon the red litmus. The iodised 

 litmus paper is preferable to iodised starch paper (Schonbein's test-paper) 

 which exhibits a blue coloration with any reagent which liberates iodine, 

 e. g., nitrous acid, chlorine, etc. From observations made with iodised litmus 

 paper Houzeau concludes that ozone exists in the air normally, but the inten- 

 sity with which it acts at any given point of the atmosphere is very variable. 

 Country air contains at most ^^Aoo of its weight or yosVoo of its volume of 

 ozone. The frequency of the ozone manifestations varies with the seasons, 

 being greatest in the spring, strong in summer, v/eaker in autumn, and weakest 

 in winter. The maximum of ozone is found in May and June, and the mini- 

 mum in December and January. In general, ozone is more frequently ob- 

 served on rainy days than in fine weather. Strong atmospheric disturbances, 

 as thunder storms, gales, and hurricanes, are frequently accompanied by great 

 manifestations of ozone. According to Houzeau, atmospheric electricity 

 appears to be the most active cause of the formation of atmospheric ozone. 



It has been found that the air immediately above the tree tops 

 and at the margin of the forest is richer in ozone than that of the 

 interior, where a portion of it is utilized by the decaying vegetation. 

 Ozone certainly aids in purifying the air by oxidizing animal or 



