On the Theory o/" Nobili's Coloured Ri?igs. 7 



These analyses give C^, H 24 , Oi as the formula for beta- 

 orcine : it is, however, perfectly empirical. When beta-orcine, 

 previously dried in vacuo, was heated in the water-bath to 

 212° F., it parted with a considerable amount of water. The 

 orcine did not become in the least degree coloured, neither 

 did it melt, though the temperature was raised to 230° F. 

 Alpha-orcine melts and becomes coloured at 212° F. A 

 quantity of beta-orcine, which had been kept four weeks in 

 the water-bath at 212° F., had lost nearly 30 per cent, in 

 weight, and was still continuing to lose weight. This how- 

 ever did not arise merely from the loss of water, but because 

 a considerable portion of the orcine itself had volatilized even 

 at the comparatively low temperature of 212° F. The quantity 

 of water which beta-orcine contains cannot therefore be deter- 

 mined by drying it on the water-bath. 



I have been unable to determine the atomic weight of beta- 

 orcine. It gives no precipitate with nitrate or ammonio- 

 nitrate of silver, with the salts of iron, baryta and copper, or 

 with neutral acetate of lead. It yields a pretty abundant 

 whitish precipitate with subacetate of lead, which is soluble in 

 an excess of the precipitant. This precipitate is exceedingly 

 alterable, and immediately becomes deep red-coloured, even 

 more rapidly than is the case with alpha-orcine in similar cir- 

 cumstances. 



Glasgow, May 22, 1848. 



II. On the Theory of Nobili's Coloured Rings. 

 By E. du Bois-Reymond and W. Beetz*. 



I. 



NOBILI first pointed out the possibility of applying the 

 coloured films [apparenze elettro-chimice) which he dis- 

 covered, to determine the diffusion of the current in nonpris- 

 matic conductors f. But with his unacquaintance of Ohm's 

 law of the motion of electricity, even according to one dimen- 

 sion, he was unable to give proper evolution to this idea. In 

 a treatise entitled Note sur les anneaux produits par le depot 

 des oxydes metalliques sur les metaux%, M. Edmond Becquerel 

 attempted to subject the simplest form of Nobili's rings to a 

 rigid investigation, both in an optical and electrical pointof view. 

 The rings were obtained by a method given by M. Becquerel, 

 senior, viz. by pouring a thin layer of a solution of oxide of 



• Read before the Physical Society of Berlin, on the 11th Dec. 1846, 

 and communicated by the Authors. 



\ Bib'iottihquc Universelle de Geneve. Anc. Ser. Sc. et Arts, 1835, t. lix. 

 pp. 263, 416. 



X Annates de Chimie et de Physique. Janvier 1845, 3 ser. t. xviii. p. 342. 



