8.  The art of using the diamond for cutting glass has undergone, within a few years, a very important improvement.  A glazier’s apprentice, when using a diamond set in a conical ferrule, as was always the practice about twenty years since, found great difficulty in acquiring the art of using it with certainty; and, at the end of a seven years’ apprenticeship, many were found but indifferently skilled in its employment.  This arose from the difficulty of finding the precise angle at which the diamond cuts, and of guiding it along the glass at the proper inclination when that angle is found.  Almost the whole of the time consumed and of the glass destroyed in acquiring the art of cutting glass, may now be saved by the use of an improved tool.  The gem is set in a small piece of squared brass with its edges nearly parallel to one side of the square.  A person skilled in its use now files away the brass on one side until, by trial, he finds that the diamond will make a clean cut, when guided by keeping this edge pressed against a ruler.  The diamond and its mounting are now attached to a stick like a pencil, by means of a swivel allowing a small angular motion.  Thus, even the beginner at once applies the cutting edge at the proper angle, by pressing the side of the brass against a ruler; and even though the part he holds in his hand should deviate a little from the required angle, it communicates no irregularity to the position of the diamond, which rarely fails to do its office when thus employed.

The relative hardness of the diamond, in different directions, is a singular fact.  An experienced workman, on whose judgement I can rely, informed me that he has seen a diamond ground with diamond powder on a cast-iron mill for three hours without its being at all worn, but that, on changing its direction with respect to the grinding surface, the same edge was ground away.

9.  Employment of materials of little value.  The skins used by the goldbeater are produced from the offal of animals.  The hoofs of horses and cattle, and other horny refuse, are employed in the production of the prussiate of potash, that beautiful, yellow, crystallized salt, which is exhibited in the shops of some of our chemists.  The worn-out saucepans and tinware of our kitchens, when beyond the reach of the tinker’s art, are not utterly worthless.  We sometimes meet carts loaded with old tin kettles and worn-out iron coal-skuttles traversing our streets.  These have not yet completed their useful course; the less corroded parts are cut into strips, punched with small holes, and varnished with a coarse black varnish for the use of the trunk-maker, who protects the edges and angles of his boxes with them; the remainder are conveyed to the manufacturing chemists in the outskirts of the town, who employ them in combination with pyroligneous acid, in making a black die for the use of calico printers.