-1859] WRITINGS OF JOSEPH HENRY. 167 



Its constant presence in the atmosphere furnishes an ex- 

 planation of the occurence of a minute quantity of mineral 

 matter in the composition of certain plants which is net 

 found in the soil in which they grow. 



Pollen oj plants . — At certain seasons of the 3'ear, the pollen 

 of the pine tree and other plants is carried to immense dis- 

 tances, and after a thunder-storm is often found on the sur- 

 face of water in our rain casks and from its yellow color is 

 frequently mistaken for sulphur. 



Ozone. — Another substance which of late years has been 

 discovered in the atmosphere by the indefatigable labors 

 of Prof. Schonbein, the inventor of gun-cotton, is known by 

 the name of "ozone," which is supposed from all the researches 

 made upon it to be oxygen in a peculiar condition, in which 

 its affinity for other substances or combining power is highly 

 exalted. When a stream of frictional electricity is made to 

 flow from the point of the prime conductor of an ordinary 

 machine, a peculiar odor is perceived, due as is supposed to 

 the oxygen of the air assuming an altered condition, and 

 hence it has been inferred that ozone consists of oxygen with 

 an extra dose of electricity. 



M. Clausius however has advanced another hypothesis 

 which appears to be in accordance with other facts, namely, 

 that an ordinary atom of oxygen, of which the atomic weight 

 is eight, is in reality a molecule composed of two atoms, 

 and that under the influence of electrical repulsion these 

 atoms are separated, and in the unneutralized affinity, con- 

 sequent upon this separation, the increased avidity of com- 

 bination is evinced. 



Whatever be the nature of ozone, it is certain that it pos- 

 sesses great powers of combination with many other sub- 

 stances, and thus tends to produce chemical eff"ects. It is 

 • probably produced on a large scale in the atmosphere, on 

 the same principle by which it is obtained in the laboratory, 

 namely, by the electrical discharge in the form of lightning 

 from the clouds. 



The test for ozone consists of one part of iodide of potas- 

 sium, ten parts of starch, and one hundred parts of water, 



