reddish tint arising from a maximum or excess of manganese; or, if the glass be previously colourless, it will cause a greenish tint to appear, which the manganese had dissipated: therefore, carbon would seem to be a neutralizer of oxygen, and practically a dissipater of the colour, caused by manganese. But should the Glass thus lowered in tint be re-melted, or only softened by the drop pincher, in moulding it into prisms or ornamental drops, the reddish tint will again appear; as if (which is probably the case,) the carbon received in the annealing had again been dissipated, and replaced by oxygen in the process of pinching. However massive may be the piece of flint Glass, which is the medium of these changes, the purple tint of the manganese, the greenish hue from iron, (the impurities of the lead or other ingredients,) not only adhere to the surface of the Glass, skin-deep, but extend to every particle of the central and general mass. That these alternate changes are the result of two antagonist chemical agents appears confirmed by the fact of Glassmakers resorting to carbon for the neutralization of the manganese reddish tint, when in excess in the fluid Glass; this is done by agitating it in the pot with a wooden pole or burning staff, the carbon from which is found to have the effect of dissipating the manganese colour. An excess of nitrate of potash or soda has somewhat the same colouring effect as manganese, arising probably from its abundance of oxygen.*