INTllODUCTOIlY LECTURE. 
657 
tilling the tar we obtain a residuum of pitchy a material of 
many well-known iises^ and an inflammable liquid commonly 
called coal-tar naphtha. This coal-tar naphtha, submitted to 
repeated fractional distillations, yields very many valuable 
products. Thus, we get liquids capable of being burned in 
lamps, and thereby used as sources of heat and light. We 
also obtain the remarkable fluid called benzol, a material 
extensively employed in the manufacture of varnishes, and 
as a detergent, so to speak, to grease-stained fabrics. By 
acting on benzol with nitric acid, it is converted into artificial 
oil of bitter almonds, and used as a cheap substitute for the 
true oil by the perfumer and confectioner, for the purposes 
of communicating odour and flavour. When artificial oil of 
bitter almonds has passed through particular series of opera¬ 
tions, it is transformed into those beautiful colouring matters, 
or dyes, mauve and magenta, the manufacture of which has 
employed thousands of persons, and actually made the 
fortunes, and great ones too, of many others. Besides 
benzol, from tar we obtain carbolic acid—an antiseptic and 
caustic which, in the hands of some practitioners, has, it is 
said, rendered good service to the veterinaiy art. These are 
only a few examples, selected at random, of the materials of 
practical utility which have been drawn from the well of 
science by the labours of the chemist. 
if we were to turn to agriculture, an art intimately con¬ 
nected with your own, we should find that she is much 
indebted to the chemist for the assistance he has furnished, 
not only in reference to the composition of crops, soils, 
manures, &c., but likewise in pointing out to the farmer 
the most profitable and best way of feeding and fattening 
his cattle; also in preventing him from being cheated in the 
purchase of manures, the various oil-cakes, and in many 
other ways that I cannot allude to here. One might cite 
thousands of applications of chemical science similar to the 
last two, but it will, I am sure, gentlemen, be more inter¬ 
esting to you if I now briefly refer to the aid which the same 
science has given, and continues to render, to many of the 
different departments of medical knowledge with which you 
will be expected to acquaint yourselves. 
The information revealed to you by anatomy, which teaches 
you the shape, structure, and relative positions of the organs 
of an animal, would be incomplete without you also knew of 
what they were each chemically composed. 
It is, however, to physiology—that most interesting study 
which makes us acquainted with the duties performed by the 
various organs while in a state of health—that chemistry has 
rendered espeeial service. Without the assistance of this 
