1 44 CHE MIS TR V FOR A GRICUL TURAL STUDENTS 



of the heavier hydrocarbons carried up with the 

 vapour of the lighter hydrocarbons. Heat the flask very 

 cautiously at first by means of a water bath, and avoid having 

 any light near. Then, when nothing further distils, the flask 

 may be safely heated by means of a Bunsen burner. Should, 

 at first, some incondensible gas be obtained, collect a tube full 

 by downward displacement ; ignite it, and note that it burns 

 with a flame much more luminous than pure marsh gas, for it 

 contains hydrocarbons richer in carbon. As the temperature 

 shown by the thermometer gradually rises, collect liquid 

 fractions below 200° (light petroleum) and between 200° and 

 400° (heavy petroleum). Pour a few drops of each upon the 

 hand, and note the difference in the volatility. Allow the 

 residue to cool in the flask to obtain the semi-solid hydro- 

 carbon residue. 



Fig. 47. 



To Illustrate the manufacture of coal gas by the destructive 

 distillation of coal, employ the apparatus figured. Roughly 

 powder some coal, introduce into a Florence flask, and heat 

 strongly. Pass the volatile products of distillation through a 

 flask containing water in order to separate condensible 

 products, and collect the purified coal gas in a cylinder over 

 water. Ignite a cylinder of the gas. Note that it burns with a 

 flame more luminous than the wood gas, indicating the 



