398 Scientific Intelligence. 



platinum tube containing anhydrous sodium fluoride (since it is 

 not hygroscopic is preferable to the potassium salt), Moissan has 

 been able to determine the density of fluorine. The pure gas 

 was collected in platinum flasks of about 100 c. c. capacity, pre- 

 viously filled with nitrogen. After weighing, the fluorine was 

 brought in contact with water and the evolved gases were meas- 

 ured and analyzed, a correction being made for any remaining 

 nitrogen. The mean density found was 1"265, while that required 

 by theory (F = 19) is 1-316.— C. R., cix, 861; J. Chem. Soc 9 

 lviii, 201, March, 1890. G. f. b. 



4. On the Determination of Oxygen dissolved in Water. — 

 Thresh has proposed a new method of determining the oxygen 

 which is dissolved in water, founded on the fact that a very 

 minute quantity of a nitrite is able to cause the liberation of a 

 very large amount of iodine when to a water containing it and 

 oxygen, potassium iodide and sulphuric acid are added; the 

 nitrogen oxide seeming to act as a carrier. Since the iodine thus 

 set free is capable of accurate estimation, the oxygen dissolved in 

 a drinking water may be very rapidly determined in this way 

 and with great precision. For this purpose it is necessary simply 

 to add to a known volume of the water a definite quantity of 

 sodium nitrite together with an excess of potassium iodide and 

 sulphuric acid, and, avoiding access of air, to determine volumet- 

 rically the amount of iodine liberated. Deducting the quantity 

 corresponding to the nitrite used, the remainder represents the 

 oxygen dissolved in the water. The strength of the solutions 

 used and the apparatus employed in the determination are noted 

 in the paper. — J. Chem. Soc., lvii, 185, March, 1890. g. f. b. 



5. On a Method of distinguishing Hydrogen Arsenide from 

 Hydrogen Antimonide. — Beunn has observed that hydrogen 

 sulphide and hydrogen arsenide do not act on each other in tlie 

 absence of air either in the gaseous state or in solution in water, 

 even on exposure to direct sunlight; but that on the admission 

 of air, arsenous sulphide is at once produced, and in both cases, 

 a mixture of hydrogen arsenide and air in a flask over water 

 deposited a brown-black precipitate ; thus confirming the observa- 

 tion of Janowsky. But the author shows that this precipitate 

 varies in its composition according to the amount of oxygen 

 present. With an excess of air the hydrogen arsenide is oxidized 

 to black metallic arsenic ; while if only a small quantity of air 

 be mixed with the gas, it is oxidized only to brown solid hydro- 

 gen arsenide. Hence it would appear that the above reaction of 

 H 2 S upon H 3 As takes place in two stages ; the H 3 As being, oxi- 

 dized to arsenic in the first ; and in the second the arsenic being 

 converted into sulphide. On heating a mixture of hydrogen 

 arsenide and hydrogen sulphide, however, to 230°, even when 

 absolutely free of air, decomposition takes place and arsenous 

 sulphide is deposited. Further experiment showed that hydro- 

 gen arsenide is itself decomposed at about this temperature, and 

 that therefore the formation of arsenous sulphide is a secondary 



