388 EECENT PEOGEESS IN PHYSICS. 



SchonLein has the great credit of having restored this question to 

 the current of scientific activity. He has shown that the electrical odor 

 comes from a peculiar gas, produced during the electrical emission, 

 which he calls ozone. He has investigated the properties of this sub- 

 stance for years with the greatest zeal, and although, as yet, it has 

 not been obtained in an isolated state, many of its important chemical 

 and physical relations have been ascertained, and further researches 

 on the subject promise most interesting discoveries in the field of 

 chemistry. 



The first memoir of Schonbein on ozone is in the ^^ De.nkscliriften 

 der Mundieuer Akademie." It is also printed in Poggepdorf's Anna- 

 Itn. Bd. L. p. 616. 



A small pamphlet with the title, " On the pi^oduction of ozone in the 

 chemical ivay," evidently by Schonbein, was published in 1844 by 

 Schonbein & Schweighaiiser, in Basel. 



The most important treatises on this subject which then followed 

 are to be found in Poggendorfs Annalen, by reference to the index of 

 names, appended to the LXXV volume. 



In these papers the historical course of Schonbein's discoveries may 

 be followed out. I will omit this historical investigation on account 

 of its great extent, and I will not refer to the contents of the separate 

 paj)ers, but describe the most essential experiments which show the 

 nature and most important relations of ozone, in the order in which 

 Professor Schonbein had the goodness to show them to me in the year 

 1849, and, passing over their earlier phases, present his views upon 

 its nature as now held, after many years investigation. 



The prime conductor of an electrical machine being provided at the 



Fig. 82. end with a round-pointed wire, a, b, about 1 line in 



diameter, (fig. 82.) When the machine is turned the 



peculiar electrical odor will be perceived in the vicinity 



of the end a of the wire. 



That this odor is not to be ascribed to a mere subjec- 

 tive affection of the organ rf smell, but is owing to a 

 peculiar gas, is certain from the fact that this odorous 

 principle produces a series of chemical and physical 

 effects, having the greatest similarity to the chemical 

 reactions and physical relations of other gases. Indeed, 

 Schonbein has succeeded in preparing this odorous prin- 

 ciple, ozone, in a purely chemical way, and in producing 

 the same reactions with it which are observed when elec- 

 tricity is issuing from points. 



If we hold before the point, at the distance of about ^ or 1 inch, a 

 piece of paper covered with a paste of starch and iodide of potassium, 

 the paste will at once turn blue. 



To make this preparation two teaspoons full of starch with a small 

 crystal of iodide of potassium are to be boiled to a paste, with ten 

 times their volume of water. 



The ozone acts upon this paste as chlorine does ; it decomposes the 

 iodide of potassium, and the iodine set free, colors the starch blue. 



