Intelligence and Miscellaneous A7iicles. 237 



the many discoveries, and great and important truths, he has so 

 laboriously proved and so freely given to the world. 



I have the honour to be. Gentlemen, ■• 



Yours very respectfully, 



Thomas Woods, M.D. 



OBSERVATIONS AND EXPERIMENTS UPON THE EMPLOYMENT OF 

 IODIDE OV POTASSIUM AS A REAGENT FOR OZONE. BY S. CLOEZ. 



The experiments of Marignac, Fremy, and Becquerel have done 

 most to clear up the question of the nature of ozone ; they prove 

 completely the possibility of imparting to chemically pure oxygen 

 all the properties of this mysterious substance. 



Iodide of potassium being one of those substances upon which 

 ozone is capable of acting, paper soaked in a solution of starch con- 

 taining 0*002 of its weight of this iodide has been proposed, under 

 the name of the ozonometric reagent, not only to indicate the presence 

 of ozone, but also to measure the quantity contained in the air. If 

 the coloration of this paper could only be produced by ozonized 

 oxygen, its employment would leave nothing to be desired. But 

 this is not the case ; acid vapours act upon iodide of potassium in 

 the same manner as active oxygen ; the essential oils exhaled by plants 

 have the same action, and prove that moist air, under the influence 

 of the direct light of the sun, colours the reagent, although we can- 

 not suppose the air to be ozonized. 



The experiments upon nitrification which the author is carrying 

 on simultaneously at the Museum of Natural History and the Poly- 

 technic School, have led him to investigate what part the ozonized 

 oxygen said to exist in the air may play in the formation of nitric 

 acid. After a great number of trials he has not yet succeeded in 

 establishing with certainty the part taken by ozone in the phseno- 

 menon of nitrification, effected in the absence of azotized or ammo- 

 niacal substances, but his experiments have convinced him that the 

 numerous attempts to prove the presence of ozone in the air and 

 measure, its quantity by means of iodized paper, are not of the least 

 value. 



It is an admitted fact that the coloration of the paper takes place 

 every day in the country, and in places where there are many trees 

 and an active vegetation, whilst many observations prove that in the 

 most populous parts of towns the paper is very rarely and very 

 slightly coloured. The author has found that in the Garden of Plants 

 the iodized paper is constantly coloured by exposure, especially in 

 the neighbourhood of resiniferous trees, and frequently in a very short 

 time, but that at the Polytechnic School, in the vicinity of which 

 there are few trees, but a dense population living in unhealthy houses, 

 the paper exposed daily to the air under the same conditions as that 

 at the Museum has not been coloured once in six months. M. Cahours 

 has observed a similar contrast between his garden at Neuilly and 

 the Hotel des Monnaies in Paris. 



Resiniferous trees, aromatic plants, and all the parts of vegetables 

 which contain volatile oils, act much more strongly than inodorous 



