206 ANNUAL KECORD OF SCIENCE AND INDUSTRY. 



METALLIC BARIUM. 



Although the compounds of barium have been so long and 

 so thoroughly known, the metal itself has been but little 

 studied. Sergius Kern, of St. Petersburg, has lately suc- 

 ceeded in preparing it by several methods in a state suitable 

 for examination. The best process seems to be to heat ba- 

 rium iodide with metallic sodium. A violent reaction ensues, 

 accompanied by an evolution of heat and light ; the resulting 

 mass is treated with mercury to form a barium amalgam, from 

 which, finally, the mercury is distilled. The barium so obtain- 

 ed resembles calcium very closely, is apparently tough and 

 ductile, and has a specific gravity of 3.75. 1 A, Jane 4, 243. 



PURIFICATION OF TIN BY FILTRATION. 



Curter has proposed an interesting method of freeing tin 

 from less fusible metals by means of filtration. The filter 

 was constructed as follows: Common tinned iron of ordi- 

 nary thickness was cut into strips about 150 millimeters 

 long by 100 wide. Five hundred of these, with their sur- 

 faces parallel, were wedged together in an oblong iron frame, 

 and this frame was tightly fitted into an opening in the bot- 

 tom of a large graphite crucible. The tin to be purified was 

 then melted in another crucible, and allowed to cool until 

 crystals began to form on its surface, when it was transferred 

 to the above-described filter. Of course the heat sufficed to 

 melt the tinning of the iron strips, thus leaving narrow 

 spaces between them through which the molten metal could 

 flow, its solid impurities remaining behind. More than fifty 

 centners of impure Bohemian tin was thus rendered almost 

 chemically pure, the iron, copper, and arsenic with which it 

 had been contaminated being left, alloyed with some of the 

 tin itself, upon the filter. 14 C,March } 469. 



THE ARTIFICIAL IMITATION OF NATIVE MAGNETIC PLATINUM. 



It is known that occasional pieces of native platinum not 

 only act upon the magnetic needle, but are themselves mag- 

 netic, like the true iron magnets. Berzelius and Kokscharof 

 have contributed somewhat to our knowledge of the chem- 

 ical and other properties of this platinum, and have shown 

 that there is always a certain quantity of iron associated in 



