656 
INTllODUCTOllY LtCTUllE. 
ture of theory and practice together. I think I may say, 
without fear of contradiction, that there arc very few pursuits 
but what liave been benefited, more or less, by chemistry; 
and just to give you an instance of the valuable services 
which she has rendered to man by administering to his 
every-day requirements, I will relate a few facts taken from 
the liistory of the gas called chlorine. For ages the vege¬ 
table fibres flax and cotton have been woven into linen and 
calico—two materials of clothing sought after by rich and 
poor, and which, when they leave the looms, have a brown 
colour. In order to remove this objectionable brown colour, 
it was customary until, 1 believe, about eighty years ago, for 
spinners in this country to ship their raw linen and calico 
to Holland, where these fabrics were spread out on extensive 
lawns, so that they might be subjected to the bleeching action 
exerted by the combined influences of sun, air, and moisture. 
This Dutch mode of bleaching required weeks, and, if the 
weather proved unfavorable, months, for its completion, and 
then the goods had to be returned to England. We thus sec 
that, while dependent on the Dutch, the operation of bleaching 
was one involving the consumption of much time, the risk of 
loss by shipwreck, and the sinking of a great amount of 
capital. In the year 1784, Scheele discovered chlorine, and 
noticed that, whether in the state of gas or dissolved in 
water, it enjoyed the property of depriving many vegetable 
substances of their colour in a few minutes or, at most, in a 
few hours. It was, however, reserved for Berthollet, an 
eminent French chemist, to successfully apply this fact to 
the bleaching of textile fabrics on the large scale. The con¬ 
sequence of its application was, that the spinner could invest 
less capital, a new branch of trade sprang up which gave 
employment to thousands of persons, and the public gene¬ 
rally were supplied with two of the most useful articles of 
clothing at a much cheaper price than hitherto. 
The manufacture of coal-gas affords us another and less 
hackneyed illustration of the beneficial influence of chemistry 
on the progress of the useful arts. When coal was first 
employed as a source of illuminating-gas, and for many years 
afterwards, the tar, and the watery fluid produced along with 
the gas itself, were looked upon as worthless. Within a 
comparatively short period the chemist, by his investigations, 
originally conducted in the cause of pure science only, dis¬ 
covered a mine of wealth in the waste or by-products already 
named. That is to say, from the once worthless gas-water, 
agriculture and medicine are now supplied with the various 
compounds of ammonia which they require. By dis- 
