oTO SEC. 13. CHEMISTRY. 



vacuum through a thin porous septum. The results proved that the diffusion 

 rates of the gases closely correspond with the law which has already been 

 given, and quite excluded the idea of capillary transpiration, which would 

 give for the same gases an entirely different result. 



2546. Apparatus employed in experiments on Absorption 

 and dialytic separation of Gases by Colloid Septa. 



(1.) Waterproof silk bag for the dialysis of air. When the bag is ex- 

 hausted by means of a Sprengel pump the air which penetrates the 

 walls of the bag is found to contain 42 per cent, of oxygen, that is, 

 the per-centage of oxygen present is doubled. 



(2.) The penetration of metals by gases was studied by the aid of metallic 

 tubes, of which the palladium tube shown is one. It was enclosed 

 in a tube of glass or porcelain, and rendered vacuous by the aid of a 

 Sprengel exhauster ; a stream of gas was then passed through the 

 annular space between the tubes. In the cold no hydrogen will pass 

 through palladium, but at a red heat the gas passes at a rate of 

 nearly 4,000 cubic cent, per square metre of surface in a minute. 



2603. E. Mitscherlich's Vapour Density Apparatus. 



Prof. A. Mitscherlich) Munden. 



This apparatus is described in E. Mitscherlich's text-book of chemistry, 

 p. 308, and was employed by him in determining the specific gravity of 

 vapours. 



II. MODELS, DIAGRAMS, APPARATUS, AND CHEMI- 

 CALS EMPLOYED IN OR RESULTING FROM 

 CHEMICAL RESEARCH. 



2407. Apparatus by which Dr. Andrews and Professor Tait 

 proved that ozone is a condensed form of oxygen. 



Dr. Andrews, F.R.S. 



Dry oxygen gas is exposed to the action of the silent electrical discharge in 

 a glass tube terminating in a U tube containing sulphuric acid, which indicates 

 by its change of position the change of volume in the gas. 



2409. Apparatus used for ascertaining the Density of 

 Ozone. J- Louis Soret, Geneva. 



This process, based upon the velocity of diffusion, has been described in 

 detail in the " Recherches sur le Deusite de 1'Ozone " (Archives des Sciences 

 physiques et naturelles, 1867, Vol. 30, p. 328., Annales de Chiniie et de 

 physique, 1868, Vol. 13, p. 264). Constructed by the Geneva Association 

 for the Construction of Scientific Instruments. 



2547. Apparatus for Gas Experiment, as used for the 

 determination of the Composition of Ozone. 



Sir B. C. Brodie. 



This apparatus will be described in the form in which it was employed for 

 the determination of the composition of ozone, the object being to determine 

 the changes which electrized oxygen underwent when subjected to the action 

 of heat or of chemical reagents. 



