its Relations with Agriculture. 
821 
rarely submitted to the distillatory process just referred to. 
It occurred, however, to Mr. Murdoch, exactly a hundred years 
ago, to light his house by gas so obtained. Yet tlie discovery 
made such slow progTCss that when I went to Paris thirty-five 
years after Murdoch’s ajiplication of coal-gas for illuminating 
purposes, the Rue de Rivoli was, I believe, the only street lighted 
by its means. At the present time not less than seven millions 
of tons of coal are annually used in the public gas-works of the 
United Kingdom alone. During the process of distilling gas a con- 
siderable quantity of tarry substance comes ovei’, and along with it 
a certain amount of watery matter. The former, known as coal- 
tar, for many yeai’s in my life was burnt or run away, and all 
the watery portion, containing the nitrogen in the form of ammo- 
nia, found its way also into the drains which led to the rivers. 
Chemistry afterwards opened out extensive fields for the utilisation 
of this liquid tarry hydrocarbon, and the ammonia for some years 
past has been converted into sulphate, and handed over to the 
husbandman as a source of nitrogen for his growing crops. If all 
the coal ti’eated in our gasworks were made to yield its ammonia, more 
than 60,000 tons of the sulphate would be produced, worth, at less 
than half its former price, about 600,000^. a year. To this sum has 
to be added the value of the tar. 
We are probably within the mark in saying that more than 
fifteen million tons of coal are annually coked for the use of our 
ironworks. The whole of this is effected in ovens where the gas is 
burnt under conditions which preclude the possibility of any tar or 
ammonia being rendered available. My firm were early adven- 
turers in the field for avoiding this terrible waste in this country. 
Tlie coal was placed in ovens, which were virtually retorts ; the gas 
evolved during the process was passed through a series of con- 
densers, which intercepted the tar and the ammoniacal solution, and 
the gaseous hydrocarbons, thus purified, were used for heating the 
oven. Coke so made, however, was found less suitable for blast- 
furnace work than that obtained by direct application of heat to 
the surface of the coal, and the plan, to our disappointment and 
regret, was abandoned. Thus is incurred an annual loss of 
sulphate of ammonia worth considerably above a million sterling. 
From both these sources of ammonia— gasworks and occasionally coke 
ovens — 9,000 to 10,000 cubic feet of gas per ton of coal is obtained, 
and a quantity of sulphate represented by something under 5 lb. of 
ammoniacal gas. 
Of the pig-iron pi’cduced in Great Britain about one million 
tons are obtained by the use of raw coal, of which about two tons 
are required per ton of metal, capable of furnishing about 17,000 
tons annually of sulphate of ammonia. The success which had 
attended the extraction of ammonia from the gas made for illumin- 
ating purposes led the Scotch ironmasters to consider the feasibility 
of applying condensers to the gases as they leave their blast- 
furnaces. In the blast-furnace, however, not only are the 10,000 
cubic feet of hydrocarbons to be gasified, but all the fixed carbon, 
