DETECTION OF UNOXIDIZED PHOSPHORUS. 279 



Fah. In case the paper is not colored black after 

 some time, unoxidized phosphorus cannot be present, 

 and it is then unnecessary to proceed further by the 

 methods III. and TV. The operator may go on to (VL). 

 If, on the other hand, the paper blackens, this is no 

 certain evidence of the presence of phosphorus, because 

 various substances, viz., hydrosulphuric acid (detectable 

 by means of a slip of paper moistened with solution of 

 lead or terchloride of antimony), formic acid, products 

 of putrefaction, &c., may produce the same result. 

 Proceed then with the substance as directed in III. and 

 IV. 



III. The luminosity of phosphorus, of all its charac- 

 ters, furnishes the most striking evidence of its presence 

 in the free state. A large sample of the substance is 

 accordingly examined by the following well-proved 

 and admirable method of E. Mitscherlich. 



Mix the substance under examination with water 

 and some sulphuric acid, and subject the mixture to 

 distillation in a flask, A. (See Fig. 43.) This flask is 

 connected with an evolution-tube b, and the latter again 

 with a glass cooling or condensing tube, c c c, which 

 passes through a perforated cork, a, in the bottom of a 

 cylinder, B, into a glass vessel, C. Cold water runs 

 from D, through a stopcock, into a funnel, i, which 

 extends to the bottom of B ; the warmed water flows 

 off throuh g* 



Now, if the substance in A contains phosphorus, 

 there will appear, in the dark, in the upper part of the 

 condensing tube at the point r, where the aqueous 

 vapors, distilling over, enter that part of the tube, a 

 strong luminosity, usually a luminous ring. If you 

 take for distillation 5 oz. of a mixture containing only 

 ? ! th of a grain of phosphorus, and accordingly only 1 



* Instead of this vertical condenser, an ordinary glass one used 

 for distillation may be substituted. 



