ucts have in this country until recently been allowed to escape as
waste, but the time is approaching when these must be utilized. It will
give an idea of the industrial importance of coke when it is stated, that
about twelve million tons of our coal annually undergo conversion into
this form of fuel. Chemically considered, coke consists of carbon together
with all the mineral constituents of the coal, and small quantities of
hydrogen, oxygen, and nitrogen. The amount of carbon varies from 85 to 97,
and the ash from 3 to 14 per cent.

The conversion of coal into coke is a very venerable branch of
manufacture, which was first carried out on a large scale in this country
about the middle of the seventeenth century. As an operation it may appear
utterly devoid of romance, but as Goethe has described his visit to the
earliest of coke-burners, this fragment of history is worth narrating.
When the great German philosophical poet was a student at Strassburg
(1771), he rode over with some friends to visit the neighbourhood of
Saarbruecken where he met an old "coal philosopher" named Stauf, who was
there carrying on the industry. This "philosophus per ignem" was manager
of some alum works, and the ruling spirit of the "burning hill" of
Duttweiler. The hill no doubt owed its designation to the coke ovens at
work upon it, and which had been in operation there for some six or seven
years before Goethe's visit, _i.e._ since 1764. The coke was wanted for
iron smelting, and even at that early period Stauf had the wisdom to
condense his volatile products, for we are told that he showed his
visitors bitumen, burning-oil, lampblack, and even a cake of sal ammoniac
resulting from his operations. Goethe has put upon record his visit to the
little haggard old coke-burner, living in his lonely cottage in the forest
(_Aus meinem Leben: Wahrheit und Dichtung_, Book X). It is probably
Stauf's ovens which are described by the French metallurgist, De Gensanne,
in his _Traite de la fonte des Mines par le feu du Charbon de Terre_,
published in Paris in 1770. After long years of coke-making, without any
regard to the value of the volatile products, we are now beginning to
consider the advisability of doing that which has long been done on the
Continent.

It is not unlikely that Bishop Watson in the last century had heard of
the attempt to recover the products from coke ovens, for he gives the
following very sound advice in his _Chemical Essays_:--