Mr. J. Apjohn on Cadmium. 77 



drop out of the upper vessel unless an e(]ual volume of air 

 can enter it ; and that no fluid can enter the lower vessel un- 

 less an equal volume of air can escape from it. Both of these 

 conditions are fulfilled by means of the connecting tube c : 

 for every drop of liquor that falls into the lower vessel expels 

 its own bulk of air ; and this air having no other means of 

 escape passes along the connecting tube to the upper vessel, 

 where exactly that bulk of air is required to compensate the 

 vacuum that would have otherwise been so far formed, by the 

 loss of the drop of liquid which had fallen through the funnel 

 pipe. Thus the transfer of the liquor takes place from the 

 upper to the lower vessel, as also the compensating transfer of 

 air from the lower to the upper vessel ; and this goes on to the 

 end, the alkali being only exposed to the same portion of air 

 during any period of time, be it ever so long, that may be re- 

 quired for the completion of the process. 



It is to be observed that this apparatus should be made of 

 green glass, it being much less acted on by fixed alkalies than 

 white. A white glass bottle containing solution of caustic 

 potash will often be cracked by it in every direction, and in a 

 singular manner. 



This apparatus is extensive in its utility : it answers for the 

 filtration of any liquid where either the carbonic acid or the 

 moisture of the atmosphere would be injurious. It is also well 

 adapted lor the filtration of volatiles, as alcohol, ethers, am- 

 moniacal liquors, &c., the vapours beijig thus eflfectually con- 

 fined. And by substituting a stratum of coarsely powdered 

 flints in the usual manner, instead of the roll of linen, we may 

 filter corrosive acids, which would be weakened by access of 

 air. — Dublin Phil. Journ. 



ON CADMIUM. BY JAMES APJOHN, M.B. 



In examining a slag produced in the smelting of galena, I 

 have succeeded in detecting the presence of cadmium, a metal 

 hitherto unknown in this country [Ireland]. Prof Stromeyer, 

 of Gottingen, was the first who described this substance, which 

 was found by him in zinc brought from Silesia. Its principal 

 properties and combinations were fully explained by this dis- 

 tinguished chemist. It was subsequently found by Ur. Clarke 

 of Cambridge to exist in minute quantity, in some of the 

 spelter ores of Mendip and Cornwall. 



Of the slag in which I have discovered it, it constitutes, by a 

 single trial, 5-05 grs. per cent. From a subse(]uent experiment, 

 however, I am disposed to think that the average [)roportiou 

 in which it enters into the composition of tlie slag is not so 



lu<rh. 



