444 CONSIDERATION OF CARBON COMPOUNDS. 



filled. Upon heating the combustion-tube in a suitable furnace, the 

 organic matter is burned by the oxygen of the cupric oxide, the 

 hydrogen is converted into water (steam), which is absorbed by the 

 calcium chloride, and the carbon is converted into carbon dioxide, 

 which is absorbed by the potassium hydroxide. The apparatus repre- 

 sented in Fig. 68 shows the gas-furnace in which rests the coinbustion- 



FIG. 68. 



Gas-furnace for organic analysis. 



tube with calcium chloride tube and potash bulb attached. Upon 

 re-weighing the two absorbing vessels at the end of the operation, the 

 increase in weight will indicate the quantity of water and carbon 

 dioxide formed during the combustion, and from these figures the 

 amount of carbon and hydrogen present in the organic matter may 

 easily be calculated. 



For instance : 0.81 gramme of a substance having been analyzed, 

 furnishes, of carbon dioxide 1.32 gramme, and of water 0.45 gramme. 

 As every 44 parts by weight of carbon dioxide contain 12 parts by 

 weight of carbon, the above 1.32 gramme contains of carbon 0.36 

 gramme, or 44.444 per cent. As every 17.88 parts of water contain 

 2 parts of hydrogen, the above 0.45 gramme consequently contains 

 0.0503 gramme, or 6.213 per cent. 



Oxygen is scarcely ever determined directly, but generally indi- 

 rectly, by determining the quantity of all other elements and deduct- 

 ing their weight, calculated to percentages from 100. The difference 

 is oxygen. 



If, in the above instance, 44.444 per cent, of carbon and 6.213 per 

 cent, of hydrogen were found to be present, and all other elements, 



