21G James W. Helps on some 



Lampadelplioria, or torcli-raee of science began, we know — that 

 the runners are in full swing now we know — but where it will 

 end, and how long the course will take is hidden from our ken. 

 What Clytemnestra, in the old Greek Tragedy, said of the beacon- 

 fires that told her of the fall of Troy, we may say of the 

 advance of science — 



" Such is the fashion of our race of lamps, 

 Each in succession ministering to each, 

 And both alike are conquerors, first and last." 



77. — Some Coal-tar Products. 



By James W. Helps. 



(Read November 13th, 1889.) 



The subject of my paper this evening is one about which so 

 much can be said, that I feel myself placed in a position of some 

 difficulty, as it is by no means easy, in the short space of time 

 at my disposal, to give much more than a bare outline of a few 

 of the products now obtainable from coal-tar. It will not be 

 necessary for me to say much about the coal itself from which 

 the tar is produced, as probably all here know the manner in 

 which it was formed, and acknowledge its vegetable origin. 



I must first of all briefly allude to the manner in which the 

 tar is produced, and to do this must describe the earlier pro- 

 cesses in the manufacture of coal-gas. A certain quantity 

 of coal is placed in a retort made of fireclay, which is usually 

 one of several, set in brickwork and heated by one fire common 

 to all to a temperature of about 2000° F. (1100° C). This 

 retort is closed by a lid and the coal subjected to destructive dis- 

 tillation ; the volatile constituents pass off through a pipe lead- 

 ing from the mouthpiece to a vessel called the hydraulic main. 

 Now it is well known that substances require more heat to exist 

 in a gaseous than in a liquid state, consequently, immediately 

 on leaving the heated retort condemation commences, and one of 

 the first results is the production of tar. The gases are, after 

 leaving the main, conducted through a long series of pipes and 

 condensers of various kinds, until their temperature is reduced 

 to nearly that of the surrounding air ; by this means almost the 

 whole of the tar is thrown down ; what little remains is removed 

 when the gas passes tbrougli the washers and scrubbers, where 

 also the ammonia and portions of certain other impurities are 

 extracted. 



We have now obtained conl-tar, the quantity of which, result- 

 ing from the distillation of one ton of Newcastle coal, is about 



