86 Scientific Intelligence. 



2. The Oxidation of Platinum. — It has been generally sup- 

 posed, up to the present time, that metallic platinum is inca- 

 pable of being oxidized by the action of air or oxygen, and that 

 platinum-black consists of a mechanical mixture of pure plati- 

 num with condensed oxygen. The latter view does not appear to 

 be in accordance with general chemical principles, but it has held 

 its place in chemical literature, probably on account of the high 

 authority of Liebig and Dobereiner who advocated it. Lotiiar 

 Wohlee has recently described an elaborate research in regard 

 to the behavior of platinum with oxygen, and he has shown con- 

 clusively that this metal is susceptible to oxidation. The presence 

 of an oxide in platinum-black was shown by the fact that iodine 

 was set free by it from potassium iodide. It was found that 

 platinum-black, by being heated for a long time in contact with 

 oxygen, took up the latter to the extent of 1*92 per cent at 100° 

 and 2*35 per cent at 300°, although the limit of oxidation was not 

 reached. It was found that oxidized platinum-black was soluble 

 in dilute hydrochloric acid to the extent of from 10 to 18 per 

 cent of its platinum, and it was found that precipitated platinous 

 hydroxide was entirely analogous in many reactions to the oxi- 

 dized platinum-black. Moreover, grey platinum sponge, by long 

 heating in oxygen at 420-450°, was converted to the extent of 40 

 per cent into a black powder which was found to be platinous 

 oxide, although the limit of oxidation was not reached, and even 

 the oxidation of platinum foil was found to be possible, as was 

 shown by its increase in weight and very marked change in color. 



The results of this investigation are important, since they 

 furnish a satisfactory explanation of much of the chemical 

 behavior of finely divided platinum. — Berichte, xxxvi, 3475. 



h. l. w. 



3. The Production of High Vacua for Distillation. — Chem- 

 ical distillations under diminished pressure are commonly made 

 by use of the water-jet pump, but the nearest approach to a 

 vacuum obtainable with this apparatus is from 8 to 15 ram pressure, 

 according to the temperature of the water. For lower pressures 

 mercury pumps or other air-pumps may be used, but as these are 

 not always available, Ernst Erdmann has devised a process for 

 the purpose which depends upon the low vapor tension of carbon 

 dioxide at the temperature of liquid air. The apparatus to be 

 used for distillation is first exhausted by means of the water 

 pump to 30 or 35 mm , then, by means of a suitable connection pro- 

 vided with a glass stop-cock, carbon dioxide produced in a Kipp 

 generator and dried with sulphuric acid and calcium chloride is 

 admitted until the apparatus is filled with it. The apparatus is 

 then exhausted as before, and the filling with carbon dioxide and 

 exhaustion are repeated three times, when a small bulb connected 

 with the apparatus is immersed in liquid air. The pressure then 

 sinks within a minute to less than O^"" 11 , usually to 0*2 or 0*3 mm . 

 If the filling with carbon dioxide and exhaustion have been 

 repeated a fourth time the pressure is still lower, and it has been 



