INDUSTRIAL PROGRESS DURING THE YEAR 1872. X xvii 



cules of the mixed gases are passed through the sphere of 

 action of the copper salt. With tubes of the same diameter, 

 the opportunity of action is the same at all velocities; if the 

 diameters differ, the number of these opportunities is the 

 same when the velocity is inversely as the square of the di- 

 ameter of the tube. The percentage of hydrochloric acid gas 

 decomposed varies with the square root of the proportionate 

 volume of oxygen to hydrogen chloride. The cupric chloride 

 formed bears no definite proportion to the chlorine evolved. 

 Since molecules not in contact with the copper salt are in- 

 cluded in the field of action, hydrogen chloride must be de- 

 composed also as a result of the forces engaged. M. Merget 

 has made some remarkable observations upon the volatility 

 of mercury, and has made a curious application of it. He 

 finds that this metal gives off vapor continually, even when 

 frozen solid ; that this vapor may be condensed upon the sur- 

 faces of certain solids ; that it passes readily through porous 

 bodies like wood or porcelain ; and that it readily reduces 

 salts of the noble metals. If an ordinary silver negative - , 

 therefore, be exposed to the action of mercury vapor, this va- 

 por will be condensed upon the metallic portions of this neg- 

 ative ; and now, if this negative be laid upon a piece of sen- 

 sitized paper, the mercury condensed upon the negative re- 

 duces the silver in the paper, producing, entirely without 

 light, a fac simile in reverse of the original, which may be 

 fixed and toned in the usual way of treating photographic 

 prints. Davenport has investigated some points in the man- 

 ufacture of malleable iron. He shows that the silicon, the 

 phosphorus, and the manganese are not affected by the an- 

 nealing process ; that the sulphur is not diminished by it, and 

 may be increased ; and that the carbon may be reduced to a 

 mere trace. In the centre of a thick castinsr there is a dark 

 core, which contains uncombined or graphitic carbon. 



The field of Organic Chemistry has been marked by great 

 activity the past year ; though much more has been done in 

 working out old methods than in originating new theories. 

 Young and Thorpe have succeeded in breaking up or " crack- 

 ing" paraffin, converting it into liquid products. These con- 

 sist of a mixture of hydrocarbons of the marsh-gas and the 

 olefine series, thus proving paraffin to belong to the former 

 series, which are known thus to break up. Wurtz and Vogt 



