THE OXIDES OF CARBON 



loS 



pounds of carbon. Pure marsh gas has been found by experi- 

 ment to contain 75 per cent, of carbon, and 25 per cent, of 

 hydrogen. Calculate the simplest formula that would represent 

 its composition. 



XXVI. THE OXIDES OF CARBON 



It has been found that when carbon burns in air or oxygen, 

 the dioxide of carbon or carbonic acid gas, COg, is formed. 

 The gas was found to be an acidic oxide, dissolving in water 

 to form a liquid acid to litmus, and combining with lime to 

 form chalk, which is therefore carbonate of lime. As this 

 compound is a gas, it should be possible to prepare it by the 

 action of a less volatile acid upon a carbonate (see p. 77). 

 Fit up the apparatus figured. In 

 the large flask place some lumps of 

 chalk or, better, marble. Pour in 

 some water and then a little hydro- 

 chloric acid. Wash the gas by 

 passing it through a flask containing 

 water. Collect the gas by downward 

 displacement of air. Test it with a 

 taper, blue litmus solution, and lime 

 water. Is it identical with that 

 obtained by the combustion of carbon ? Determine its 

 relative density by means of the apparatus figured on p. 13. 

 For this purpose, the gas must be dried by passing it through 

 a U tube containing pumice soaked with oil of vitriol attached 

 to the flask B. 



Although carbonic acid gas does not support the combustion 

 of a taper, it may be capable of losing oxygen to other 



Fig. 43. 



