IV

PREFACE.

introductory to the rest, given a sketch of the chemicaltheory and production of Gas Light. I have pointed outthe leading objects of public and private utility, to whichthe art of lighting with gas has been, or remains to beapplied : and added such other facts and observationsas may serve to remove all doubt in the minds of thereader as to the important benefit which this country inparticular, and the world at large, have gained by thisdiscovery.

In the third part I have stated the maximum quantitiesof gas obtainable in the large way, from different kinds ofcoal.

In the fourth part, I have given a description of allthe various forms and dimensions which the distillatoryvessels or retorts have successively assumed, as well asof the improvements that have been made in the mode ofsetting the retorts, with a view to saving them from unduedeterioration, and preventing any improvident waste offuel. I have here given a particular account of the dis-tillatory apparatus now used at the most celebrated gasworks in the metropolis.

The fifth and sixth parts, lead the reader considerablyfurther into a knowledge of the economy and practiceof this art. They contain an account of a great variety ofexperiments which have been pursued on a large scale,in order to ascertain the most profitable mode of employing