CHEMISTRY. 653 



Reduction of Carbon Dioxide to Carbon Monoxide by means of Charcoal 

 (by Alexander Xaumanu and Carl Pistor). — Water-gas, formed by pass- 

 ing steam over incandescent charcoal, contains, besides hydrogen and 

 carbon monoxide, varying quantities of carbon dioxide, which is a hin- 

 drance to the economic uses of the water-gas. In the following research 

 the authors examined the chemical reactions which take i)lace under va- 

 rying temperatures, and with different quantities of charcoal. The tem- 

 peratures were determined by inserting in the heated tube (combustion 

 tubing 82 centimeters long) substances having well-established melting 

 p)oints, such as lead chloride (501°), silver pyrophosphate (585°), silver 

 (9540), &c. 



Experiments determine that the lowest temperature at which the re- 

 duction of carbon dioxide to monoxide by charcoal begins lies between 

 530° and 585°, say 550°, provided the gas be passed not too rapidly 

 and the charcoal layer be 06 centimeters long. 



With a charcoal layer only 10 centimeters long a much higher temper- 

 ature is necessary, between 634° and 703° G. The amount of carbon 

 dioxide reduced increases with the rise of temi)erature. For the table 

 giving results of eleven experiments under varying conditions, we refer 

 to the original article. {Ber. d. cliem. Ges., xviii, 1G47.) 



Preparation of Cyanogen in the Wet Way (by G. Jacquemin). — The 

 usual process, by the action of a concentrated solution of cupric sul- 

 phate on a saturated solution of potassium cyanide is incomplete, only 

 half the cyanogen being evolved. In the process of the author all the 

 cyanogen of the potassium cyanide is obtained and the gas is pure. 



Two parts of cupric sulphate dissolved in four parts of water are 

 ])laced in a retort or in a flask, on a water-bath, and, by means of a 

 stoppered funnel, a concentrated solution of one part of pure potassium 

 {;yaiiide is gradually introduced. The reaction begins violently at ordi- 

 nary temperatures and when the evolution slackens the temperature of 

 the water-bath is elevated to quicken it. Ten grams of chemically i)ure 

 KCN give 850 c. c. of pure cyanogen. Commercial KCN gives the same 

 result, but the gas sometimes contains traces of CO2. 



There are two processes for withdrawing the cyanogen of the copper 

 cyanide. 1. Decant the liquid remaining in the retort or flask, wash 

 by decantation, and add a slight excess of ferric chloride of 30° B., or 

 higher. The action commences in the cold and a slight elevation of the 

 temperature produces an abundant evolution of cyanogen. The ferric 

 chloride passes to the state of ferrous chloride in transferring the cop- 

 ])er cyanide to chloride, which sets free the cyanogen and forms cuprous 

 chloride which turns to cupric chloride at the expense of the excess of 

 })ersalt of iron. 2. Add to the washed copper cyanide some manga- 

 nese peroxide and acetic acid. Heat slightly. Acetates of copper and 

 manganese are formed and cyanogen is evolved. When the operation 



