Properties of Pure Substances : Nitrogen. 5 



tronbiesome, and I have not been able to find any information 

 as to whether phosphorus absorbs gases which might be given 

 off during the process of the removal of oxygen from air. 

 Warburg used a solution of potassium permanganate to absorb 

 the vapour of phosphorus ; but I have not been able to obtain 

 information as to whether such a solution is to be relied on, 

 in the first place to remove all the phosphorus, and in the 

 second to give off nothing else during the process. I 

 understand, from the paper in Wied. Ann. vol. xl. 1890, p. 1, 

 that Warburg, in his later experiments, did not succeed to his 

 satisfaction in removing the last trace of oxygen by this 

 method, but had to electrolyse the glass of his vacnum-tubes 

 so as to liberate tbe sodium in presence of the nitrogen, in 

 order to get rid of the last traces of oxygen and hydrogen. 

 This method appears satisfactory if one has at one's disposal 

 a sufficient electromotive force, suitable glass, and an infinite 

 time : the hydrogen appears to be absorbed as by palladium. 



Another method over which I spent six months of fruitless 

 labour is based on the decomposition of ammonium bichromate 

 by heat. This method is convenient, because if the bichro- 

 mate could be got to deliver nitrogen of suitable quality, 

 small quantities of the salt could be decomposed in bulbs 

 fused on to the vacuum-tubes along with suitable purifying 

 reagents. Ordinary ammonium bichromate (i. e. that sold as 

 pure) gives off a good deal of ammonia and oxides of nitrogen 

 as well as nitrogen itself and water-vapour. This means the 

 use of a good many purifying reagents, so that the method 

 loses its advantages of simplicity ; and in addition the oxides 

 of nitrogen cannot be fixed satisfactorily by any suitable 

 reagent known to me. I thought, however, that possibly 

 very pure ammonium bichromate might decompose in a 

 simpler manner, and consequently went to great trouble to 

 procure a pure sample. For this purpose I purified a large 

 quantity of ammonium chloride and sulphate by the method 

 described by Stas (Bull, cle V Academie Royale de Belgique, 

 2nd ser. t. x. p. 283), repeating the boiling with nitric acid 

 more often than Stas found requisite. The purified samples 

 were used to generate gaseous ammonia (under the influence 

 of specially prepared marble-lime), which after copious wash- 

 ing was absorbed by chromic acid. Some samples of this 

 ammonia were passed over red-hot platinized asbestos with 

 sufficient pure oxygen* to destroy three quarters of the 

 ammonia, 4NH3 + o0 2 = GH 2 0-f-2N 2 , with a view to destroy- 

 ing any traces of organic ammonium compounds; but the 



* The method of procuring- pure oxygen will be described in another 

 connexion. 



