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212 reason to believe that water or its vapour confer volatility, even in the slightest degree, upon those substances which when alone have their limits of vaporization at temperatures above ordinary occurrence, and that consequently natural evaporation can produce no effects of this kind in the atmosphere.

It would also appear that nitrate of ammonia, corrosive sublimate, oxalic acid, and perhaps oxalate of ammonia, are substances which evolve vapour at common temperatures.

Royal Institution, Aug. 30, 1830.

Fluidity of Sulpher at Common Temperatures.

placed a Florence flask containing sulphur upon a hot sand-bath, it was left to itself Next morning, the bath being cold, it was found that the flask had broken, and in consequence of the sulphur running out, nearly the whole of it had disappeared. The flask being broken open, was examined, and was found lined with a sulphur dew, consisting of large and small globules intermixed. The greater number of these, perhaps two-thirds, were in the usual opake solid state; the remainder were fluid, although the temperature had been for some hours that of the atmosphere. On touching one of these drops, it immediately became solid, crystalline, and opake, assuming the ordinary state of sulphur, and perfectly resembling the others in appearance. This took place very rapidly, so that it was hardly possible to apply a wire or other body to the drops quick enough to derange the form before solidity had been acquired; by quick motion, however, it might be effected, and by passing the finger over them, a sort of smear could be produced. Whether touched by metal, glass, wood, or the skin, the change seemed equally rapid; but it appeared to require actual contact; no vibration of the glass on which the globules lay rendered them solid, and many of them were retained for a week in their fluid state. This state of the sulphur appears evidently to be analogous to that of water cooled whilst quiescent below its freezing-point. The same property is also exhibited by some other bodies, but I believe no instance is known where the difference between the