DESTRUCTIVE DISTILLATION. 183 



takes place, a large variety of substances being formed. Coke, is 

 left behind in the vessel, being non-volatile, whilst a mixture of 

 volatile products passes off; some of which will condense to 

 liquids on cooling, whilst others will not. 



Obtain a clay tobacco pipe and fill the bowl with small pieces 

 of coal. Make a covering over the bowl with good clay so as to 

 enclose the coal in a vessel having as outlet only the shank of the 

 pipe. Dry the prepared and charged pipe in an oven, and plaster 

 up with fresh clay any cracks that may form, repeating the opera- 

 tion until the pipe is covered with an air-tight lid of clay. Now 

 heat the bowl either by placing it in an ordinary fire, or by means 

 of a large Bunsen lamp ; in a short time gas will be formed by the 

 action of the heat on the coal, and will issue from the stem of the 

 pipe so as to burn steadily when a light is applied. 



In this way the production of " tar " is not perceptible ; instead 

 of a tobacco pipe, employ a piece of thin glass tube 8 or 10 inches 

 long and J inch diameter internally, drawn out and sealed up at 

 one end in the lamp flame (Expt. 48) like a test-tube. When cold 

 introduce a small teaspoonful of powdered coal into this tube, 

 shaking it down to the sealed-up end, and then apply heat, holding 

 the tube by a clamp-holder (fig. 12) in a nearly horizontal position ; 

 the coal will be decomposed as before, and inflammable gas will 

 pass off at the mouth of the tube, where it can be lit ; between the 

 heated part of the tube and the mouth a brown evil-smelling thick 

 liquid will condense on the glass, and also a little watery fluid 

 which will not mix with the brown tar. 



By using a small glass retort instead of the tube a larger supply 

 of condensed tar and watery fluid may be obtained. On testing the 

 watery fluid with a sensitive test paper, such as a red litmus paper 

 (Expt. 142), you will observe that it has an alkaline reaction, being 

 in fact a very impure solution of ammonia ; so that besides coke 

 three other products are evidently formed by the decomposition, 

 viz., the inflammable gas (itself a mixture of several constituents) ; 

 the watery fluid, containing dissolved ammonia gas and other sub- 

 stances ; and the tar. In large gas works these two latter sub- 

 stances are carefully condensed, and certain impurities removed 

 from the gas before it is supplied to our houses for burning pur- 

 poses ; from the watery fluid ammonia and various compounds 

 thereof are obtained ; whilst the tar serves as the source of a large 

 number of useful products; amongst which may be mentioned 

 artificial oil of almonds (nitrobenzol), used for scenting soap and 

 similar purposes ; and many beautiful dyestuffs. 



Expt. 201. Destructive Distillation of Wood. The term 

 "destructive distillation" is applied to the process of heating 



