26 report— 1865. 



ethereal solution of bromo-benzoL, and of bronio-toluol whilst submitted to a 

 current of carbonic anhydride, as, for instance, may be explained by the 

 equation — ■ 



Bromobenzol. Sodic benzoate. 



G c H 5 Br-{-Na 2 +Ge 2 =Na G G H ; (G OJ+NaBr, 



or such as those of Maxwell Simpson and of Baeyer on the artificial formation 

 of tribasic acids ; and, referring to methods of research, stress might be laid on the 

 important aid afforded by the extended use of the am tlgam of sodium as a redu- 

 cing agent, and on the similar but still more remarkable reducing-elfects of hy- 

 driodic acid, — processes, indeed, not new, but the value of which till quite recently 

 has only been partially recognized. 



Passing allusion only can now be made to some of the processes of mineral and 

 metallurgic chemistry, such as the improvements in the details of the process for 

 preparing magnesium., the comparative facility with which the recently discovered 

 metals thallium, rubidium, aud caesium and their compounds may be obtained, 

 and the application by Redtenbacher of his observation of the sparing solubilitj' of 

 their alums to the extraction of the new alkalies from the lithium residues of com- 

 merce. Of indium, too, the latest of the newly discovered metals revealed by the 

 spectrum, it must suffice to say that it has been obtained in quantity which places 

 its existence as a distinct metal beyond question. I am indebted to my iriend 

 Professor Roscoe for the small specimens of the metal and its sulphide now upon 

 the table. 



An extensive branch of industry is now springing up in the improved methods of 

 voltaic deposition of the metals. Weil has, by the use of an alkaline solution of 

 tartrate of copper, contrived to coat iron and steel with a tough closely adherent 

 sheathing of copper, by simply suspending the articles to be coated by means of a 

 wire of zinc in the metallic bath. No battery is required. Lead and tin may in a 

 similar manner be deposited on copper, iron, or steel, if the oxide of tin or of lead 

 be dissolved in a bath of strong solution of caustic soda. 



I must, before I conclude, advert to one or two interesting additions to our 

 knowledge upon the side where chemistry and physics meet. Few results, perhaps, 

 were more unexpected than those obtained by Deville aud Troost upon the per- 

 meability to gases of certain dense metals at elevated temperatures. They have 

 proved that platinum andiron, when white-hot, become for the time porous, and are 

 rapidly permeated by hydrogen, which will even pass out under the pressure of the 

 atmosphere and leave a vacuum almost perfect within the tube, in one form of 

 these experiments, tubes of hammered and of cast platinum (which in one case was 

 as much as a twelfth of an inch in thickness) were fitted by means of corks into 

 the axis of a shorter and wider tube of glazed porcelain; a slow current of pure and 

 dry hydrogen was then maintained through the porcelain tube, whilst a current 

 of* dry air was transmitted through the platinum tube. At ordinary temperatures 

 no change was observed in either gas. A tire was then lighted around the outside 

 of the porcelain tube, and gradually raised until the heat became very intense. 

 At 2000° Fahr. the oxygen contained in the air had entirely disappeared; nothing 

 but nitrogen mixed with steam passed out of the platinum tube, hydrogen had 

 passed through the pores of the platinum and entered into combination with the 

 oxygen of the air within; whilst at still higher temperatures the moist nitrogen 

 became mixed with hydrogen. As the tube cooled, the same phenomena occurred 

 in the inverse order, till, when the ordinary temperature had been regained, no 

 diffusion of hydrogen was perceptible, and unaltered air was collected from the 

 platinum tube. Analogous results were obtained when a tube of soft cast steel was 

 substituted for that of platinum, though the thickness of the steel tube was an 

 eighth, or in some cases as much as a sixth of an inch. 



From these experiments one practical conclusion deducible is, that air-pyrometers, 

 the bulbs of which are formed of iron or platinum, cannot be relied on when em- 

 ployed for measuring elevated temperatures ; glazed porcelain, however, was found 

 to confine the gases completely. 



Curious as these results are, they are but parenthetical in another series of more 



