Coal-tar Products. 219 



capable of holding about 1200 gallons, which quantity is run 

 into it at the top. The fire is lighted at B, and as the tar 

 warms distillation commences. This is at first attended with 

 some danger, as the water m the tar causes it to rise and froth ; 

 the firing must therefore be conducted with great care, to avoid 

 sudden boiUng over. Vapours soon issue from the pipe C, at the 

 top of the still ; these are at first composed of water and the 

 more volatile oils, called Fikst Kunnings, and after leaving the 

 still they are led through a worm condenser, which is kept 

 immersed in a vessel containing water, constantly on the flow. 

 As these vapours condense, they pass on to a receiver ; this 

 vessel is provided with as many outlets as there are fractions 

 to collect, each leadmg to a different stove-tank. As soon 

 as these vapours nearly cease, the receiver is changed, and 

 the temperature in the still (which so far has been kept below 

 a certain point) increased. The distillation now becomes more 

 rapid, and vapours are given off, which are condensed and 

 collected under the name of Light Oils; these processes are 

 repeated, and in turn the vapours of Carbolic Oil, Creosote 

 Oil, and Anthracene Oil are distilled over, condensed, and 

 collected. The prmcipal guide which the attendant has to 

 assist him, in making the different changes, is the thermometer 

 in the still ; but he has also to note the smell, specific gravity, 

 and quantity of the distillates. It Is usual to change at the fol- 

 lowing points : — 



First runnings up to 105° or 110° 0. 

 Light oils „ 210° 



Carbohc oils „ 240° 



Creosote oils „ 270° 

 Anthracene oils above that. 



After the anthracene oil ceases to flow, the residue is known 

 as Pitch. This is allowed to cool, and carefully run out into 

 proper receptacles. 



The quantities of each of the above-mentioned substances, 

 which can be obtained from a charge of 1200 gallons of tar, vary 

 so much according to its quality and mode of distillation, that it 

 is not easy to arrive at a satisfactory average. 



According to Watson Smith, 1000 gallons of Lancashire tar, 

 chiefly from Cannel coal, gave the following results : — 



Per cent. 



Ammoniacal liquor 25 2-2' 



First runnings 38 2*2 



Light oils 131 10-61 



Creosote oils 87 7-6 j by weight. 



Anthracene oils 191 16.9' 



Pitch 31 60-5j 



