The refractive indices of nicotine

Measurements of the refractive indices of nicotine have been made by Gladstone and Dale and by Brühl. Their numbers are lower throughout than those now submitted. The instruments and hollow quartz prism used were the same that were employed for the measurement of the refractive indices of water, and had more recently been used for measuring the refractive indices of benzene and cyclo-hexane. At the outset a difficulty was encountered. When the hollow quartz prism was filled with water, its sides having previously been held in position by rubber bands, all air bubbles got rid of and the stopper sealed with mercury, the sides were held firmly in position by atmospheric pressure alone and there was no further trouble. But with benzene and cyclo-hexane this was not the case, and rubber bands of any kind were quickly attacked and made useless. It was, therefore, necessary to attach the sides to the body of the prism by some sort of aqueous cement. The glycerine jelly used by microscopists for mounting was found to meet all requirements. But it was soon found that nicotine was a solvent of all the gelatines, gums, rubber, wax and paraffins of different melting points that were tried, and that any cements made of them were quickly attacked. The only thing remaining seemed to be to complete the polishing of the body of the prism, which had until now been left in the grey, and to place the sides in optical contact with it, a somewhat risky and delicate operation, which was successfully carried out by Messrs. A. Hilger, Ltd. Some rather troublesome reflections from the newly-polished surfaces had to be masked out and then further trouble from the prism was at an end.