430 M. Verdet on the Optical Properties developed in 



that of water. It is therefore probable that the magneto-rotary 

 power of the salts of lanthanium is negative ; but as 1 did not 

 analj'ze the solution, this is not perfectly certain. 



Mohjbdenum, — Some metallic molybdenum which was fur- 

 nished me by M. Debray is magnetic; and as this property also 

 exists in molybdic acid, purified by repeated distillations, it can- 

 not be attributed to the presence of foreign substances. Molyb- 

 denum, therefore, must be added to the list of magnetic bodies. 

 The soluble molybdates which I had at my disposal — the mo- 

 lybdates of soda and ammonia — are diamagnetic. Their mag- 

 neto-rotary power is positive, but small. 



Aluminium. — M. Deville has placed aluminium among the 

 feebly magnetic metals. The analogy between aluminium and 

 iron has caused this result to' be regarded as very probable. 

 Nevertheless I have not been able to find any compound of this 

 metal which was not diamagnetic. Even alumina, when quite 

 pure, is repelled by an electro-magnet. Having in fact obtained 

 some perfectly pure and strongly diamagnetic nitrate of alumina 

 from the Ecole Normale, I got from it, by calcination, some anhy- 

 drous alumina which was also strongly diamagnetic. I deter- 

 mined, moreover, the magneto-rotary powers of alum, sulphate 

 of alumina, chloride of aluminium, and of the double chloride of 

 aluminium and sodium, and I found them positive. In the cases 

 of the chloride and of the double chloride, the rotary forces 

 were considerable. 



Finally, I made use of the means offered me by the chemical 

 collections of the Ecole Normale and the Faculte des Sciences, 

 for subjecting to magnetic action compounds of a certain number 

 of rare metals, which have of late years been submitted to new 

 and profound study. The subjects of these experiments were 

 zirconium, glucinum, lithium and tungsten. All the pieces of 

 these several metals, which were furnished me by MM. Debray, 

 Tr;)ost, and Riche, with the exception of a piece of glucinum, 

 ap]ieared sensibly attracted by the poles of an electro-magnet. 

 But all their pure compounds, especially their oxides and chlo- 

 rides, are incontestably diamagnetic, and all their compounds, 

 whose liquidity or solubility allowed of an examination of their 

 optical properties, had a positive magneto-rotary power. Mag- 

 nesium behaved in the same manner. A piece of distilled mag- 

 nesium given me by ]\I. Troost appeared magnetic; but pure 

 magnesia, which was prepared by calcining pure and diamagnetic 

 nitrate, was diamagnetic. The magneto-rotary power of all 

 magnesian salts is negative. 



From these experiments it seemed to me to be probable that 

 aluminium, zirconium, lithium, magnesium, and tungsten are 

 really diamagnetic. One can scarcely understand, in fact, how 



