Evulsion, the bubbling up of any fluid. The term is most commonly applied to that bubbling which happens by the application of fire, though that which ensues on the mixture of an acid and alkali is sometimes also distinguished by the same name. Boiling, in general, is occasioned by the discharge of an elastic fluid through that which is said to boil; and the appearance is the same, whether it is common air, fixed air, or steam, that makes its way through the fluid. The boiling of water is proved by Dr Hamilton of Dublin, in his essay on the ascent of vapour, to be occasioned by the lowermost particles of the water being heated and rarified into vapour by reason of the vicinity of the bottom of the containing vessel; in consequence of which, being greatly inferior in specific gravity to the surrounding fluid, they ascend with great velocity, and lacerating and pushing up the body of water in their ascent, give it the tumultuous motion called boiling. That this is occasioned by steam, and not by particles of air or fire, as some have imagined, may be very easily proved in the following manner: Let a common drinking glass be filled with hot water, and then inverted into a vessel of the same: as soon as the water in the vessel begins to boil, large bubbles will be observed to ascend in the glass, which will displace the water in it, and in a short time there will be a continual bubbling from under its edge; but if the glass is then drawn up, so that its mouth may only touch the water, and a cloth dipped in cold water be applied to the outside, the steam within it will be instantly condensed, and the water will ascend so as to fill it entirely, or very nearly so. See the article Evaporation.

trade and manufactures, is a preparation given to divers sorts of bodies by making them pass over the fire, chiefly in water, tho' sometimes in other liquors. In this sense we speak of the boiling of salt, boiling of sugar, copperas, &c.

Boiling of Silk with Soap is the first preparation in order to dyeing it. Thread is also boiled in a strong lixivium of ashes to prepare it for dyeing.

the culinary art, is a method of dressing meats by coking in hot water, intended to soften them, and dispose them for easier digestion. The effects of boiling are different according to the kinds and qualities of the water. Pulses boiled in sea-water grow harder; mutton boiled in the same becomes softer and tenderer than in fresh water, but tastes saltish and bitter.

Boiling to Death (caldariis decoquere), in the middle ages, a kind of punishment inflicted on thieves, false coiners, and some other criminals.

Boiling, is also a method of trying or effaying the goodness or falseness of a colour or dye. The stuff is to be boiled in water with certain drugs, different according to the kind or quality of the colour, to try whether or no it will discharge, and give a tincture to the water. With this view crimson silks are boiled with alum, and scarlets with soap, in quantity equal to the weight of the silk.

Boiling Wells, in natural history. See Burning-Springs, and Iceland.