586 REPORT— 1902. 



these colloids seem to be marked by the extreme readiness with which the 

 hydroxyl element replaces more or less chlorine, and by the number of molecules 

 of water with which they will combine. 



2. On Fluorescent and Phosphorescent Diamonds. 

 By Dr. J. H. Gladstone, F.R.S. 



In the ' Oomptes Rendus,' 134, M. Chaumet describes the fluorescence excited 

 in diamonds by violet light, and considers that this efl'ect is strongest in the best 

 and most valuable stones. He describes an experiment with a certain yellow 

 diamond which showed no fluorescence under violet light, but after a few minutes' 

 exposure became dark brown, regaining, however, its original colour and brilliancy 

 in the course of twenty-four hours. 



This communication has led the author to refer to the fact that at the 

 Aberdeen Meeting of the British Association in 1859 he exhibited and described a 

 diamond ring, three stones in which were somewhat fluorescent by daylight, and 

 which phosphoresced in the dark after exposure to sunlight. The Rev. Dr. 

 Robinson showed this phosphorescence to his audience in one of the evening 

 lectures. These diamonds were more fully examined afterwards, and it was found 

 that they shone most brightly when exposed to the violet and ultra-violet rays ; 

 but the length of time that the phosphorescence in the dark lasted seemed to vary 

 with the manner or length of previous exposure in a way not to be easily 

 explained. This led the author to examine the very valuable jewellery of a 

 personal friend ; not one of her diamonds exhibited this phenomenon, which 

 suggested the idea that the property in question was due to some impurity not 

 usually found in diamonds of the tirst water. A few years ago Professor Silvanus 

 Thompson exhibited this ring during the course of a lecture on some phenomena 

 of light at the Royal Institution. The diamonds shone very brilliantly, but after- 

 wards they entirely lost their phosphorescent power. They were kept in the dark, 

 and in the course of a year or so the power of phosphorescing was restored, 

 though not to its former extent. These tests have been put an end to by the loss 

 of the ring tlirough a fire. 



3. Acid Esters of Methyl Succinic Acids. By Professor J. J. Sudborough, 

 Ph.i)., D.Sc, and William A. BOx\e, Ph.D., D.Sc. 



The acid esters of mono-, di-, tri-, and tetra-methyl succinic acids have been 

 prepared and their esterification constants and electric conductivities determined. 



The results of the esterification constants clearly indicate the retarding influ- 

 ence which the introduction of methyl groups has on the rate of esterification of 

 methyl hydrogen succinate. No broad generalisations can be drawn from a study 

 of the electric conductivities. 



The determination of the esterification constants of a pair of isomeric acid 

 esters derived from an unsymmetrical dibasic acid would appear to be one of the 

 best methods for ascertaining their constitutions. The following acid esters have 

 been prepared : — Methyl hydrogen succinate, m.p. 58°. xMethyl hydrogen methyl 

 succinate, an oil identical with the compound described by Braunschweig. 

 Although, theoretically, two isomeric monomethyl esters are possible, so far only 

 one has been obtained. The same ester is formed when any one of the following 

 methods is employed : (a) Partial esterification of the acid ; (b) partial hydrolysis 

 of the neutral ester ; (c) addition of methyl alcohol to the acid anhydride. 

 Methyl hydrogen cis dimethylsuccinate melting at 38°. Methyl hydrogen trans 

 dimethylsuccinate melting at 47°-5. Two isomeric methyl hydrogen gem 

 dimethylsuccinates melting at 40°-5 and 52°. Two isomeric methyl hydrogen 

 trimethyl succinates, both of which are oils. Methyl hydrogen tetrapjethyl 

 succinate, m.p. 68°. 



