[ 23J ] 



XXX. Proceedings of Learned Societies, 



ROYAL SOCIETY. 



[Continued from p. 153.] 



June 17, 1869. — Lieut. -General Sabine, President, in the Chair. 



nnHE following communication was read : — 



-*- "On the Refraction-Equivalents of the Elements." By J. 



H. Gladstone, Ph.D., F.R.S. 



This paper is a continuation of the researches on refraction which 

 have been already published by the author in conjunction with the 

 Rev.T. Pelham Dale*. 



It is divided into two parts — the data, and the deductions. The 

 data consist of the refraction-equivalents of some simple and many 

 compound bodies, calculated from the indices observed by various 

 chemists and physicists, or by the author himself, together with a 

 series of observations on about 150 salts in solution. The method 

 of examining these, and the nature of the inferences to be drawn from 

 such experiments, have already been explained in the Proceedings of 

 the Royal Society, 1868, pp. 440-444. 



The deductions consist of a comparison of the evidence bearing on 

 each elementary substance, beginning with carbon, hydrogen, and 

 oxygen, which were in the first instance determined by Landolt. In 

 the case of some elements ail the means of calculation lead to the 

 same number within probable errors of experiment ; but in the case 

 of others two or more different equivalents are indicated. Thus iron 

 has one value in the ferrous and another in the ferric salts ; and the 

 more highly oxidized compounds of sulphur, phosphorus, arsenic, 

 and nitrogen give different numbers from those given by their sim- 

 pler combinations. The refraction-equivalent of potassium is esti- 

 mated from a variety of sources, and the number thus arrived at is 

 employed for the calculation of the other metals that give soluble 

 salts, and for the radicals with which they are combined. 



The following Table (p. 232) gives the general results of these de- 

 ductions. The equivalents that have been deduced from only one 

 compound, or of which the different determinations are not fairly 

 accordant, are marked ? in the Table. 



The specific refractive energy of a body is in some respects worthy 

 of more consideration than the infraction-equivalent, since, being 

 only the refractive index minus 1 divided by the density, it is a phy- 

 sical property independent of chemical theories as to the atomic 

 weight. Among suggestive facts are noticed: — the extreme energy of 

 hydrogen ; the existence of pairs of analogous elements having the 

 same, or nearly the same, energy — as bromine and iodine, arsenic 

 and antimony, potassium and sodium, manganese and iron, nickel and 

 cobalt; and that among the metals capable of forming soluble salts 



»- Phil. Trans. 1£63, p. 317. 



