which becomes sulphate by exposure to air), is an abundant
product of the combustion of coal.

_Brande's Journal._

* * * * *

_Indigo._

This valuable plant, which gives rise to as great speculation in India,
as hops in England, is much injured by wet weather; although the
rapidity of the growth of plants during much rain, in the temperature of
the tropics, is extraordinary, yet a proportional deficiency in all that
characterizes the vegetable world necessarily follows. This we find to
be the case with all forced vegetables; and the mildness of the radish
of hastened growth, when contrasted with the highly pungent and almost
acrid flavour of the slowly and gradually advanced one, may be adduced
as explanatory of this observation. Hence, it is practically well known
to manufacturers, that the indigo plant, however fine and luxuriant, as
is the natural result of much rain, is very deficient _in produce_, and
a similar loss is experienced even if the plant, without the fall of too
much rain, has grown up under cloudy weather. Sunshine, much and
continued sunshine, is essentially necessary for the proper exercise of
those secretory organs by which this peculiar drug is formed and
perfected.

Indigo leaves produce two dyes--blue and yellow; but the refuse leaves,
when boiled for an hour and a half, will render the water yellow, tinged
with green. This water, kept boiling for two hours, (supplying the loss
by evaporation), will, when filtered, afford a precipitate, which, when
dried, will in colour be a dun-slate, and in quantity perhaps about
equal to the blue extract such leaves have produced. This observation,
as it can lead to no practical advantage, is made for the man of
science, rather than the man of business.--_Mr. C. Weston_--_in Brande's
Journal._

* * * * *

_Chain Bridge._

Mr. Disney has lately erected at his seat the Hyde, Ingatestone, Essex,
a suspension bridge of common chain, which is much cheaper than either
wood or brick. It is fifty feet long, and four feet wide. The whole cost
of material, and workmanship scarcely exceeded 30_l_. Upon a rough
estimate, a wooden bridge of the same span would have cost from 80_l_.
to 100_l_., and a high arch probably from 150_l_. to 200_l_. The piers
or posts supporting the chains are of oak, but should they in ten or
fifteen years decay, 10_l_. in money, and three days in time would set
it u