LECTURE XXV.
Of Iron.
Iron is a metal of a bluish colour, of the greatest hardness, the most variable in its properties, and the most useful of all the metals; so that without it it is hardly possible for any people to make great advances in arts and civilization.
This metal readily parts with its phlogiston, so as to be very subject to calcine, or rust, by exposure to the air. The same is evident by the colours which appear on its surface when exposed to heat, and also when it is struck with flint; the particles that fly from it being iron partially calcined. In consequence of its readily parting with its phlogiston, it is capable of burning, like wood or other fuel, in pure air.
Iron and platina have the property of welding when very hot, so that two pieces may be joined without any solder.
When iron is heated in contact with steam, part of the water takes the place of the phlogiston, while the rest unites with it, and makes inflammable air. By this means the iron acquires one third more weight, and becomes what is called finery cinder. This substance, heated in inflammable air, imbibes it, parts with its water, and becomes perfect iron again. If the iron be heated in pure air, it also imbibes the water, of which that air chiefly consists, and also a portion of the peculiar element of the pure air.
The solution of iron in spirit of vitriol produces green copperas; which being calcined, becomes a red substance, called colcothar.
The precipitate of iron, by an infusion of galls, is the colouring matter in ink, which is kept suspended by means of gum. The precipitate from the same solution by phlogisticated alkali, is Prussian blue.