494 Scientific Intelligence. 



at a red heat. If the carbon be iu excess, and the temperature be 

 not allowed to rise too hig'h, the product is carbon tetrafluoride 

 CF 4 , a colorless gas liquefying at 10° under a pressure of five 

 atmospheres. In contact with an alcoholic solution of potassium 

 hydrate, it yields potassium fluoride and carbonate. It is not 

 decomposed by the electric spark and is soluble in carbon tetra- 

 chloride, alcohol and benzene. At a red heat, the action of 

 fluorine on carbon yields a gaseous carbon fluoride which is not 

 absorbed by alcoholic potash and is almost insoluble in water 

 although it is dissolved by alcohol. — C. P., ex, 2*76; J. Chem. 

 Soc., lviii, 55V, June, 1890. g. f. b. 



4. On Selenic acid. — Cameron and Macallan have prepared 

 pure selenic acid H 2 Se0 4 and have compared its properties with 

 those of sulphuric acid. The anhydrous acid was obtained by 

 evaporating the dilute acid on the water bath and then agitating 

 it in a vacuum at 180° as long as acid distilled over. On cooling 

 the residual acid, it crystallized in hexagonal prisms ; and on 

 analysis it was found to contain 99*71 percent of H„Se0 4 . In the 

 solid form selenic acid has a density of 2*9508. It fuses at 58° r 

 giving a colorless oily liquid of density 2*6083. The presence of 

 a small quantity of water greatly lowers its freezing point, so that 

 it does not solidify until cooled to — 51*5°. It attracts moisture 

 strongly, blackens organic matter and evolves acraldehyde by its 

 action on glycerin. A solid hydrate H 4 Se0 5 , fusing at 25°, is 

 obtained by boiling the dilute acid until the temperature rises to 

 205° and then dropping a crystal of the acid into the cooled 

 liquid. When heated in a vacuum to 200°, selenic acid decom- 

 poses into selenous oxide, oxygen and water. The acid dissolves 

 sulphur at 63° with a deep indigo-blue color. Selenium when 

 thus dissolved gives a green solution and tellui'ium a purple-red 

 one, both solutions evolving selenous oxide after a time and 

 becoming colorless. Selenic oxide could not be prepared by 

 passing selenous oxide and oxygen over heated platinum sponge, 

 nor by the action of ozone on selenous oxide. But when pure 

 selenic acid was mixed with phosphoric oxide and heated to 100°, 

 crystals were obtained on cooling which on analysis gave results 

 agreeing with the formula Se0 3 . — Proc. Poy. iSoc, xlvi, 13; J. 

 Chem.. Soc, lviii, 688, July, 1890. G. f. b. 



5. On the use of the Platinum Thermometer. E. H. Grif- 

 fiths describes the form of instrument used as follows : A coil 

 of fine platinum wire was wound on a roll of asbestos paper and 

 slipped into a thin hard-glass tube. Thick platinum wires ran 

 from this coil to the top of the instrument, and the unimmersed 

 portion of the stem was surrounded by the outer tube of a con- 

 denser, and kept at a constant temperature by a flow of tap-water. 

 The resistance of this stem was so small that the change in resist- 

 ance caused by the changes in the temperature of the tap-water 

 might be neglected. The diameter of these thermometers was 

 less than -^ of an inch, and their length about eighteen inches. 

 They were extremely sensitive, and could therefore be used to 

 trace the rise in temperature due to suffusion, the freezing points- 



