188 M. Weltzien on the Formation of Iodic Acid. 



either detonates with deposition of carbon, or unites directly 

 with chlorine, forming an oily liquid like Dutch liquid. 



C 4 H 2 -fCl 2 =C 4 H 2 Cl 2 . 



Acetylene is formed by passing chloride of methyle through a 

 tube heated below dull redness, and also by passing carbonic 

 oxide mixed with vapours of hydrochloric acid over siliciuret of 

 magnesium heated to dull redness. 



Cupreous acetylene can be formed not only by means of ammo- 

 niacal protochloride of copper, but also by protochloride of 

 copper dissolved in chloride of potassium. The formation of 

 the body takes place more easily in the presence of free potash. 

 Cupreous acetylene can be obtained free from chlorine and from 

 nitrogen, but not from oxygen. It is a compound of variable 

 composition, very alterable, and analogous to an oxysulphide. 

 From the analyses made, it appeared to correspond to the 

 formula 



C 4 Cu 2 H-frcCu 2 0. 



The presence of oxygen explains its detonating properties. The 

 detonation takes place at 120°. It gives rise to water, copper, 

 carbon, and carbonic acid mixed with a little oxide of carbon. 



Acetylene* exists ready formed in coal-gas, and may be sepa- 

 rated from it as cupreous acetylene. Its presence is readily intel- 

 ligible, inasmuch as coal-gas is formed at a red heat. The pro- 

 portion is very small, not exceeding a few hundredths of 1 per 

 cent. But its presence is not without influence on the illumina- 

 ting properties ; for, from its composition, C 4 H 2 , which does not 

 differ centesimally from that of benzole, C 12 H 6 , it is easy to see 

 that its flame is fuliginous, and that a small proportion will com- 

 municate considerable luminosity to a gas which is otherwise very 

 feebly luminous. It also contributes very materially to produce 

 the characteristic odour of coal-gas. 



According to Pean St. Gilles, when permanganate of potash 

 acts on iodine or hydriodic acid, iodic acid is formed ; and he 

 uses this method for the volumetric determination of the latter 

 bodies. He does not, however, explain the reactions involved. 

 Weltzien f states that the reaction with iodide of potassium is 

 expressed as follows : — 



KI + 2KOMn 2 7 + 6HO = KOI0 5 -f2KOHO + 2(Mn 2 4 2HO). 



The formation of hydrate of potash here is interesting, and the 

 iodate obtained is so pure that this method may be used for its 

 preparation. 



* Comptes Rendus, May 19, 1862. 



f Ann. der Chem, und Pharm. vol, cxx. p. 349. 



