492 SEC. 13. CHEMISTRY. 



2536f. Chemical Preparations (41), by Fritzshe and 

 Zinin. 



Chemical Laboratory, Imperial Academy of Sciences, St. 

 Petersburg. 



2536g. Chemical Preparations (124), by Bilstein, Kuhl- 

 berg, Kurbaton, Herailian, Rudnen, and 81 preparations by 

 Wrohlesky. 



Chemical Laboratory, Technological Institute, St. Peters- 

 burg. 



2537. Pneumatic Trough used in his experiments by Dr. 

 Joseph Black, Professor of Chemistry in the University of Edin- 

 burgh from 1766 to 1799. Dr. Black was the discoverer of fixed 

 air (carbonic acid), and the author of the theory of latent heat. 



Edinburgh Museum of Science and Art. 



2538. Glass Chemical Vessels (retort, bottle, and flask or 

 receiver) used in the chemical laboratory of the University of 

 Edinburgh during the latter half of last century. Exhibited to 

 show the contrast between them and vessels used for similar 

 purposes at the present day. 



Edinburgh Museum of Science and Art. 



APPARATUS EMPLOYED BY THE LATE THOMAS GRAHAM, F.R.S., 

 MASTER OF THE MINT, IN HIS PRINCIPAL RESEARCHES BETWEEN 

 THE YEARS 1834 AND 1866. The series is interesting as showing 

 the simplicity of the appliances with which Graham worked, and 

 by the aid of which he discovered facts and established laws which 

 have since proved to be of so much importance. 



W. Chandler Roberts, F.R.S. 



2539. Tubes with discs of graphite and hydrophane employed 

 by Graham in experiments on " diffusion " of gases. 



These experiments were commenced in 1834, when the discs were formed 

 of plaster of Paris. The instrument consists of a graduated glass tube, open 

 at one end and closed at the other by the porous substance. When such a 

 diffusion tube is filled with a gas over mercury an interchange of the gas 

 and the air takes place through the porous septum. By experiments such as 

 these Graham determined the diffusion rates of different gases, and developed 

 the law that their diffusibilities vary in the inverse ratio of the square roots 

 of their densities. 



2540. The Apparatus employed for ascertaining the diffusion 

 rates of liquids (Bakerian Lecture, 1849). 



The saline solution to be diffused was placed in the inner vessel, Avhich 

 communicated freely with distilled water in the outer vessel. It was shown 

 by this means that, when two liquids of different density and capable of mix- 

 ing are placed in contact, diffusion takes place between them, much in the 

 same manner as between gases, except that the rate of diffusion, which varies 

 with the nature of the liquids, the temperature, and the degree of concentra- 

 tion, is slower. The phenomena are governed by several well ascertained 

 laws, for a brief account of which see Watts's Dictionary of Chemistry, 

 Vol. III., p. 705. 



