TRANSACTIONS OP THE SECTIONS. 63 



cr5'8tallme mass is obtained, which is readily recognized as sulphanilic acid. The 

 reaction probably occurs thus : 



, N j g A+2 H,SO,=N { geH. (HS03)+C,H3.HSO,+OH, 



li ° H 



Dimethylaniline similarly treated behaves differently, however, being converted 

 into a mouosulphonic acid. 



N jg|H,+H,SO,=x>f {CeH,(HS03)+0H,. 



CH3 CH3 



Note on Cresol Derivatives. By Henry E. Armsteong, Ph.D., F.C.S. 

 The author briefly refen-ed to the results of the preliminary examination of coal- 

 tar cresylic acid, which he had commenced in conjunction with Mr. C. L. Field, 

 and stated that the dinitrocresol described by them in a commimication to the 

 Chemical Society had since been identified with dinitroparacresol. 



On the Action of Sulphide of Methyl on Bromacetic Acid. 

 By Professor Dr. Cktjm Brown, F.B.S.E. 



On Black Deposits of Metals. By Dr. J. H. Gladstone, F.R.S. 



If one metal be thrown down from solution by means of another metal, it does 

 not always present itself of the same colour as it exhibits when in mass ; in fact 

 most metals that are capable of being precipitated by substitution may be obtained 

 in a black condition. The allied metals platinum, palladium, and iridium are 

 generally, if not always, black when thus prepared ; and bismuth and antimony form 

 black fringes, and little else. Similar fringes are also formed by gold ; but 'it also 

 yields green, yellow, or lilac metal according to circumstances. Copper when first 

 deposited on zinc, whether from a weak or a strong solution, is black ; but in the 

 latter case it becomes chocolate-coloured as it advances, or red if tlie action be 

 more rapid. Lead in like manner is always deposited black in the first instance, 

 though the growing crystals soon become of the well-known dull grey. Silver 

 and thallium appear as little bushes of black metal on the decomposing plate, if 

 the solution be very weak, otherwise they gi-ow of their proper coloui-. Zinc and 

 cadmium give a black coating, quickly passing into dark grey, when their weak 

 solutions are decomposed by magnesium. The general result may be stated 

 thus : — If a piece of metal be immersed in the solution of another metal which it 

 can displace, the latter metal immediately makes its appearance at myriads of 

 points in a condition that does not reflect light ; but as the most favourably 

 cii'cumstanced crystals grow they acquire the optical properties of the massive 

 metal, the period at which the change takes place depending partly on the nature 

 of the metal, and partly on the rapidity of its growth. 



In the production of the black deposit of the copper-zinc couple lately employed 

 by the author and Mr. Tribe to break up various compound bodies, there are several 

 stages that may be noted. At first an outgrowth of copper forms on the zinc ; 

 then while this action is still proceeding the couple itself acts upon the water or 

 the sulphate of zinc in solution, the metallic zinc being oxidized, and hydrogen 

 gas or black zinc being formed against the copper branches. This deposit" of zinc 

 was originally observed by Dr. Russell. The arrangement of the particles between 

 the two metals in connexion is supposed to be somewhat thus : — 



Cu I ZnSO, I ZnSO, | H,0 | H,0 | Zn, 



which by the conjoint polar and chemical force becomes 



Cu 1 Zn I ZnSO, | H„SO, | H,0 | ZnO. 



