PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 447 



A New Hydro-Carbon. 



M. Bechamp lately announced to the French academy a new hydro-carbon 

 in coal-tar, liaving a boiling- point midway between that of Xylol and 

 Cuinol. If it is not a mixture of these it cannot belong to the same series, 

 for Xylol is CigHio and Cumol is CisHio. The first boils at 263 deg. ; the 

 second at 299 deg-. F. 



The chairman added that there \f no link wanting in the series between 

 Xylul and Cumol, the increase being (aCH) he was, therefore, inclined to 

 believe the compound was a mixture of hydro-carbons already known. 



Metallic Coatings. 



M. AVeil explained before the French Academy of Sciences, bis prg- 

 cessess for covering metals with firmly adherent and bright layers of other 

 metals. The method C(msists in dipping the metal to be coated in a saline 

 solution of the metal to be deposited, rendered 'distinctly alkaline with 

 potash or soda, and mixed with organic matter, such as tartaric acid or 

 glycerine. In some cases it is necessary to set up, at the same time, a 

 weak Voltaic current by keeping a piece of zinc or lead in contact with the 

 metal. In this way iron or steel may be coated with copper, silver, nickel 

 and other metals. A curious fact mentioned is that a clean surface of cop- 

 per may be .coated with zinc by placing the two metals in contact in a 

 weak solution of caustic soda or potash. In the cold the deposit of zinc 

 takes place slowly, but at 100*' of heat very rapidly. 



Hardening Cast Iron. 



A patent has been issued for hardening the surface of iron castings. 

 When the piece is filed up and finished it is brought to a cherrj red heat, 

 and then immersed till quite cold in a solution composed of 1,080 grames 

 of sulphuric acid and 65 grames of nitric acid to 10 litres of water. The 

 iron is said to suffer no distortion. 



Mechanism of the Watch. 



A prize of one hundred and fifty dollars is offered by the British Horo- 

 logical Institute for the best " treatise on the detatched lever escapement 

 and its varieties." The essay must treat of the subject generally, giving 

 tables of the proportions of the various parts of the ordinary constructions, 

 and explain the effects of variations in these proportions, and the means of 

 retifying any discovered error. Various tools for effecting measurements 

 and for completing the escapement are also to be described. The essays 

 must be sent in before the 3d of March next. 



Ink Used by Arabs. 



M. Giiyon presented to the French academy a vegetable product used 

 by the African Arabs and called by them Semag. It is a resinous matter 

 exuded from the decayed parts of an arborescent species of Lentiscus, and 

 is doubtless some form of uhiin mixed with the gum resin of the plant. 

 This substance becomes intensely black after exposure to the light. When 

 mixed with mucilage it flows and works well, and resists almost every 

 agent that will not destroy paper. 



