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its fluidity in a moderate warmth. In this kind of bath,all the parts of the inner vessel will be equally heated,how unequally soever the fire be applied underneath j andthe heat may be increased nearly as far as that in whichlead begins to melt, without any danger of the mercuryevaporating. The mercurial thermometer of Fahrenheit,whose 32d division is the point at which water freezes,and the 212th that at which water boils, is raised by theheat in which lead melts to about the 550th division,and by the heat of quicksilver boiling and evaporating tothe 600th.

Though the heat, of which mercury is susceptible, isgreat in comparison with that of boiling water, it is fartoo little for many purposes for which baths are wanted.Some curious workmen, for communicating these greaterdegrees of heat equally to different subjects, as where anumber of small steel instruments is to be equally tempered,employ melted lead as an intermedium. A plate of ironfloats upon the melted lead, and receives therefrom, inall its parts, an equal heat: the pieces of steel, laid uponthis plate, acquire all at once the fame degree of heat,and are at once quenched in water; the blue or othercolours, which they successively assume, affording suremarks of the proper points of heat at which they are tobe quenched, according to the different degrees of hardnessrequired in them.

From this practice I took the hint of another metallicbath, which supplies at once both the mercurial and thelead baths. As the imperfection of mercury consists inits not bearing so great a heat, and that of lead in its notbecoming fluid with so small a one, as many purposesrequire; I have substituted one of the fusible metallicmixtures, mentioned by Sir Isaac Newton in the Philoso-phical Transactions, composed of tw T o parts of lead, three

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