210 



Mr. J. A. Kendall. 



[Jan. 17, 



medium, the amount of hydrogen gas which passes through the metal 

 at a nearly white heat is about 0*7 cub. centim. per minute. This 

 volume of course refers to hydrogen at ordinary temperatures. 



The use of this apparatus led to the discovery of a large number of 

 substances which would serve as media by allowing the transmission 

 of hydrogen. 



The list of saline bodies was extended to the bromides, iodides, and 

 fluorides of the alkaline and earth metals, but the most important 

 discovery in this direction was that vitreous bodies such as glass, and 

 even vitrified bodies as porcelain and earthenware, acted as media 

 when at a red heat. 



Attention was then directed to the use of vitreous media for several 

 reasons. 



In experiments with fused saline bodies the use of common metals 

 was precluded owing to their being corroded by fused salts, and 

 although iron is known to be permeable to hydrogen at a red heat, 

 yet its oxidi sable qualities prevented any satisfactory results being 

 obtained when it was substituted for platinum. 



However, when vitreous matters were used instead of fused salts, it 

 became possible to use other metals for these experiments. 



A number of trials were made by taking tubes of fusible soda glass. 

 A small tube of the metal to be tested was then placed inside the 

 glass, and while passing a slight current of coal-gas to prevent 

 oxidation of the metal, the glass was carefully fused on to the metal. 

 The external surface of the glass while soft was then coated with thin 

 platinum foil or with other metals. 



On connecting the inner and outer coatings with a galvanometer, 

 passing hydrogen through the tube, and then heating it to redness, the 

 usual current of electricity was produced. 



The quantity of electricity generated both with these cells and with- 

 the platinum tubes was in proportion to the surface heated . 



The most powerful effects were obtained when the metallic coating 

 was in the pulverulent form. Spongy platinum, for example, when 

 made to adhere closely to the glass gave a strong current with 

 hydrogen. 



When using thin metallic plates in the interior of the tubes it w r as 

 found necessary to employ very thin platinum foil on the exterior, as 

 the hydrogen otherwise accumulated to some extent on the inner plate, 

 thus spoiling the cell. 



A good result might often be got by painting the external surface of 

 the glass with an alcoholic solution of platinic chloride, and then 

 igniting. By this means a very thin film of metallic platinum was 

 left on the glass, and by means of a spiral of platinum wire also put 

 round the glass, sufficient conduction was obtained. 



As glass exerts only a slight action on metallic iron at a red heat, 



