Chemistry and Physics. 151 



0-4214°. Since 0*4214° X 94*6=39, the constant obtained by 

 Raoult for acetic acid, it follows that the molecular weight of the 

 peroxide from this experiment is 94*6. A second quantity of 

 0*5085 gram peroxide was then crushed in the apparatus and low- 

 ered the melting point to 15*825°; corresponding to the molecular 

 weight 98*58. Other determinations gave 92*11, 92*0 7, 93*18, 

 90*29. In a second experiment 40*05 grams of acetic acid, melting 

 at 16*675°, had its melting point lowered to 15*768° by 0*893 

 gram of the peroxide ; corresponding to a molecular weight of 

 95*87. Hence the author concludes that the molecular weight of 

 nitrogen peroxide in the liquid state at about 16° is 92 and that 

 its formula is N 2 4 . Moreover since, in the above experiments, 

 the relative number of molecules of the peroxide in a given vol- 

 ume of acetic acid was decreased from 8*97 to 0*92 without 

 changing its molecular weight it would appear that no dissociation 

 of the peroxide takes place on dilution. Experiments with nitro- 

 gen trioxide, made by passing NO through iS T 2 4 dissolved in 

 acetic acid gave no reliable results since at 16° the trioxide was 

 dissociated. — J. Chem. Soc, liii, 621, June, 1888. g. f. b. 



2. Index of refraction of metals. — A. Ktjndt gives a brief ac- 

 count of his method of making metallic prisms of extremely 

 small angle, which allow light to pass through. Most of the me- 

 tallic prisms were deposited by electrolysis upon platinized glass. 

 To accomplish this it was necessary to obtain a homogeneous and 

 plane surface of platinized glass. After many trials Kundt suc- 

 ceeded in fusing with the glass, at a low red heat, the platinum 

 layer. Vertically over a strip of this platinized glass, which was 

 placed horizontally, is an electrode of the metal which is to be 

 deposited upon the platinum. This electrode makes a small angle 

 with the horizontal surface and includes a capillary layer of a suit- 

 able electrolyte. Frequently fifty or more trials have to be made 

 before a suitable transparent wedge of the metal is formed which 

 can be used to refract light. The prisms were also formed by 

 exposing a glass plate to platinum wire raised to a white heat by 

 an electrical current. The glass becomes covered with a layer of 

 finely divided platinum. In order to form the wedge-shaped sur- 

 face a piece of platinum foil 0*015 mm thick, 6 mm broad and about 

 45 mm long was placed with the broad sides vertical closely over 

 a horizontal glass plate. In this way a double wedge is formed 

 on the glass, consisting of a mixture of platinum oxide and plati- 

 num. By slight warming, the mixture can be converted into 

 pure platinum. These metallic wedges were also formed in a 

 vacuum by the above process, with very small angle of prism. 



The simple expression for index of refraction is N= — =r- , in 



which N is index of refraction, 8 is angle of prism and a the 

 deviation of the ray. These small quantities were measured by 

 the micrometer of a Meyerstein spectrometer. Various control 

 methods were employed to secure accuracy of measurement. 

 The velocity of light in silver is nearly four times greater thau 



