Pray, is the white lead with which houses are painted prepared by oxydating lead? MRS. B. Not merely by oxydating, but by being also united with carbonic acid. It is a carbonat of lead. The mere oxyd of lead is called red lead. Litharge is another oxyd of lead, containing less oxygen. Almost all the metallic oxyds are used as paints. The various sorts of ochres consist chiefly of iron more or less oxydated. And it is a remarkable circumstance, that if you burn metals rapidly, the light or flame they emit during combustion partakes of the colours which the oxyd successively assumes. CAROLINE. How is that accounted for, Mrs. B.? For light, you know, does not proceed from the burning body, but from the decomposition of the oxygen gas? MRS. B. The correspondence of the colour of the light with that of the oxyd which emits it, is, in all probability, owing to some particles of the metal which are volatilised and carried off by the caloric. CAROLINE. It is then a sort of metallic gas. EMILY. Why is it reckoned so unwholesome to breathe the air of a place in which metals are melting? MRS. B. Perhaps the notion is too generally entertained. But it is true with respect to lead, and some other noxious metals, because, unless care be taken, the particles of the oxyd which are volatilised by the heat are inhaled in with the breath, and may produce dangerous effects. I must show you some instances of the combustion of metals; it would require the heat of a furnace to make them burn in the common air, but if we supply them with a stream of oxygen gas, we may easily accomplish it. CAROLINE. But it will still, I suppose, be necessary in some degree to raise their temperature? MRS. B. This, as you shall see, is very easily done, particularly if the experiment be tried upon a small scale. --I begin by lighting this piece of charcoal with the candle, and then increase the rapidity of its combustion by blowing upon it with a blow-pipe. (PLATE XII. fig. 1.) [Illustration: Plate XII. Apparatus for the combustion of metals by means of oxygen gas. Fig. 1. Igniting charcoal with a taper & blow-pipe. Fig. 2. Combustion of metals by means of a blow-pipe conveying a stream of oxygen gas from a gas holder.] EMILY. That I do not understand; for it is not every kind of air, but merely oxygen gas, that produces combustion. Now you said that in breathing we inspired, but did not expire oxygen gas. Why, therefore, should the air which you breathe through the blow-pipe promote the combustion of the charcoal? MRS. B. Because the air, which has but once passed through the lungs, is yet but little altered, a small portion only of its oxygen being destroyed; so that a great deal more is gained by increasing the rapidity of the current, by means of the blow-pipe, than is lost in consequence of the air passing once through the lungs, as you shall see-- EMILY. Yes, indeed, it makes the charcoal burn much brighter. MRS. B.