Properties of Pure Substances : Nitrogen. 15 



water any smell of phosphorus can be detected. (/3) is a 

 good deal more delicate than (a), for I clearly discerned the 

 smell of, phosphorus after the pentoxide had become pure 

 enough to yield no perceptible particles when thrown into 

 water. (2) A small porcelain crucible was filled with the 

 pentoxide to be tested, the lid was replaced, and the crucible 

 rapidly raised to a dull red heat, or till the pentoxide just 

 began to distil off. The room in which the operation was 

 conducted was quite dark except for the fickle light emitted 

 by the Bunsen flame used in heating the crucible. As soon 

 as the proper moment arrived the observer adjusted the cru- 

 cible tongs with one hand and turned out the Bunsen with 

 the other. The cover of the crucible was then removed, and 

 by turning on a tap ready to hand a jet of oxygen was caused 

 to impinge on the phosphorus pentoxide in the crucible : if 

 any phosphorus is present " sparkles " are seen on the sur- 

 face of the pentoxide ; and if the room is dark and the eyes 

 of the observer sensitive this is a very good test, but not 

 quite so good as that by the smell caused by throwing a large 

 quantity of the pentoxide on water. (3) A few drops of a 

 solution of chloride of gold in ether were mixed with about 

 500 cub. centim. of water, so as to make a very dilute solution. 

 This solution was divided into two parts and occupied two 

 similar cylinders. To one portion the solution obtained by 

 throwing about 1 gramme of the pentoxide into 100 cub. 

 centim. of water was added, and to the other an equal quan- 

 tity of pure water. The observation, lasting for several days, 

 consisted in watching the cylinders and noting the reduction 

 of gold that took place, as evidenced by the rosy purple 

 colour which the solution assumed. This test is not so deli- 

 cate as the others, and is valueless unless a control experiment 

 is made in the manner here described. 



As tested by these tests, the phosphorus pentoxide prepared 

 by myself was never quite free from phosphorus, and I was 

 therefore obliged to undertake the distillation of the raw 

 product in a stream of oxygen. This of course involved the 

 making of the oxygen in a sufficient state of purity. For- 

 tunately the presence of nitrogen in oxygen used for this 

 purpose is of no consequence so long as the amount is not 

 large, the impurities to be dreaded are hydrocarbons and 

 chlorine. The oxygen was consequently prepared from po- 

 tassium chlorate with the usual precautions as for an organic 

 analysis, being passed through several potash-tubes and wash- 

 bottles on its way to the gas-holder — a large copper one free 

 from grease on the taps. From the gas-holder the oxygen 

 passed through the following system : — 



