1902.] Isomeric Change in Benzene Derivatives. 15tf 



Numerous experiments at different temperatures were made when 

 stream-line motion was maintained in the pipe, and the relation of 

 velocity to slope of pressure was determined by logarithmic plotting, 

 giving a series of lines, the " logarithmic homologues " at different tem- 

 peratures. The positions of these lines were found to be in substantia] 

 agreement with those calculated from the equations of motion. Similar 

 experiments for eddy motion were made and the logarithmic homo- 

 logues were also plotted, and their intersections with the corresponding- 

 ones for streamdine motion determined. These intersections give the 

 minimum critical velocity, and were found to lie very approximately on 

 a straight line in the diagram. 



The law of variation of critical velocity, r c , with temperature was 

 found to be 



v e ~ l x 1+0-03368T + O000156T-, 



where T is the temperature Centigrade, which agrees very closely with 

 the known variation in the viscosity of water, viz., 



/x" 1 x 1 + O03368T + O000221T 2 ; 



and it may, therefore, be concluded that over the range of temperature 

 examined the critical velocity of water in small pipes varies directly as 

 the viscosity. 



" Isomeric Change in Benzene Derivatives — The Interchange of 

 Halogen and Hydroxyl in Benzenediazonium Hydroxides."" 

 By K. J. P. Orton, Ph.D., M.A., St. John's College, Cam- 

 bridge, Demonstrator of Chemistry, St. Bartholomew's 

 Hospital. Communicated by Professor H. E. Armstrong,. 

 F.B.S. Eeceived December 1, — Eead December 4, 1902. 



In discussing the laws which govern substitution in the case of 

 benzenoid compounds, Armstrong, in 1887, drew special attention to 

 the peculiar behaviour of amido- and hydroxy-compounds, from which 

 he inferred that the phenomena of substitution were less simple than 

 was commonly supposed. He showed that there was evidence that 

 the formation of para-derivatives was preceded by that of an isomeric- 

 compound formed by the displacement of the aminic hydrogen or 

 hydroxylic hydrogen, and pointed to the probability that this might 

 prove to be true also of ortho-compounds. 



Since that time, it has been experimentally demonstrated by various 

 chemists that the radicles, CI, Br, I, NO-?, S0 3 H, can all be introduced 

 in place of the hydrogen of the amino-group of anilines and of the 

 imino-group of anilides, and that the compounds thus formed can be 



N 2 



