1900.] P. Mukerji — Method of detecting free Phosphorus, 97 



the sound from A is heard. Then, from the observation of the time since 

 leaving the station, an observer can find the distance BH, if the speed of 

 the railway train be known. AB can be found by direct measurement, 

 and thence AH. The ratio of All to BH gives that of the velocity of 

 the sound to that of the train. 



IV. — Note on a method of detecting free Phosphorus. — By P. Mukerji, 

 B.Sc, Professor of Chemistry, Presidency College, Calcutta. Com- 

 municated by the Natural History Secretary. 



[Received 12th March ; Read 4th April, 1900.] 



The following statement is made in Roscoe's Treatise on Chemistry 

 and in Watts' Dictionary of Chemistry : Phosphorus does not directly 

 combine with Hydrogen. 



The principle employed for the detection of free Phosphorus in the 

 present note is the phosphorescence of the vapour of Phosphorus diluted 

 with Hydrogen gas. 



The following is the apparatus employed : A three-necked Woulffe's 

 bottle ; to the middle neck of which there is attached by a cork a tube 

 about eleven inches long and of half an inch diameter, the upper end of 

 the tube being closed with a cork. To another neck a safety funnel with 

 a long tube is attached, and in the third neck a short jet is inserted. The 

 tube of the safety funnel dips into the liquid in the bottle ; the middle 

 tube and the jet enter the bottle only for a short distance. The tube 

 attached to the middle neck is somewhat loosely fitted so that traces of 

 air may enter the bottle. The jet and the funnel are fitted tightly. 

 The capacity of the bottle may be a litre or less. 



For the above-mentioned apparatus a simpler one has been substi- 

 tuted in several experiments ; namely, a small flask of about 184 c.c. 

 capacity, and fitted with a funnel with a stopcock and also with a jet. 



The method of carrying out the test, and the appearance : — Zinc and 

 dilute Sulphuric acid are introduced into the bottle, and the gas issuing 

 from the jet is observed. If in a dark room, there is no glow perceived, 

 then the materials employed are free from uncombined Phosphorus. 

 When the bottle is so hot through the chemical action between the zinc 

 and acid that it can scarcely be touched, i.e., when the temperature 

 of the liquid is about 60° to 70° O., and that of the gas in the upper part 

 of the bottle is 45° to 50° 0., the cork is removed from the top of the 

 tube attached to the middle neck and the substance suspected to be 

 J. ii. 13 



