Ozone and the Atmosphere. 205 



And as nothing is easier than the introduction of minute 

 amounts of impurities into chemicals manufactured on a large 

 scale, the necessity of analyzing each sample of potassium iodide 

 employed in the making of ozonoscope s, is evident. 



In order that no unnecessary element of uncertainty, however 

 should be introduced into the comparison of the various ozone 

 tests employed in this investigation, the potassium iodide was 

 especially made for the purpose. The following method was 

 found convenient, and yielded excellent results : 



36 grms. of iodine were introduced into a flat-bottomed half- 

 litre flask, with 250 c. c. water, and then 12 grms. of clean 

 piano-forte wire added in successive portions. The action at first 

 was slow, but increased with the liberation of heat due to chem- 

 ical combination, and at the close was accelerated by heating on 

 a water-bath, until all brown color had disappeared. To the 

 filtrate, which was of a greenish color, 12 grms. of iodine were 

 added. Potassium carbonate, prepared by ignition of potassium 

 bitartrate,was added, to decided alkaline reaction, and the flask 

 heated on a water-bath, until the precipitate separated in the 

 form of ferrosoferric hydrate. This precipitate, after filtering, 

 was evaporated to dryness, and washed out carefully to obtain 

 the last portion of potassium iodide. The filtrates were evap- 

 orated, and two portions of crystals, amounting to 13.5 grms. 

 and 11 grms., of pure potassium iodide obtained from them. 

 The mother-liquor was then evaporated to dryness, alcohol of 

 85 per cent, added to dissolve out the iodide and get rid of ex- 

 cess of potassium carbonate, the potassium iodide crystallized 

 from the alcoholic solution, and washed with absolute alcohol 

 yielding 29.5 grms. of the salt. The total yield was 54 orms. 

 instead of 62, the theoretical amount. 



Starch : — In order not to spend time unnecessarily in the 

 examination of starches from various sources, a skillful phar- 

 maceutist furnished me with arrow-root starch, which he had as- 

 sured himself by microscopic examination contained no sub- 

 8 tances of organic origin other than the starch granules. Tins 

 was washed with large excess of cold distilled water, until the 



