(257)
but a short coldness; or at two, three, or four several times, if you desire, that the produced coldness should rather last somewhat longer than be so great. Stirre the powder in the Liquor with a stick or whalebone (or some other thing, that will not be injur'd by the fretting Brine, that will be made) to hasten the dissolution of the Salt; upon the quickness of which depends very much the intensity of the Cold, that will ensue upon this Experiment. For the clearing up whereof, I shall annex the following particulars.
1. That a considerable degree of Cold is really produced by this operation, is very evident: First, to the touch; Secondly, by this, that if you make the Experiment (as for this reason I sometimes chuse to do) in a Glass-Body or a Tankard, you may observe, that, whilst the Solution of the Salt is making, the outside of the Metalline Vessel will, as high as the mixture reaches within, be bedew'd (if I may so speak) with a multitude of little Drops of Water, as I have * * In the History of Cold. elsewhere shown that it happens, when mixtures of Snow and Salt, being put into Glasses or other Vessels, the aqueous vapors, that swim to and from the Air, and chance to glide along the sides of the Vessels, are by the coldness thereof condens'd into Water. And in our Armoniack Solution you may observe, that if you wipe off the Dew from any particular part of the outside of the Vessel, whilst the solution does yet vigorously goe on, it will quickly collect fresh Dew, which may be sometimes copious enough to run down the sides of the Vessel. But Thirdly, the best and surest way of finding out the Coldness of our Mixture is that, which I shew'd you by plunging into it a good seal'd Weatherglass furnish't with tincted Spirit of Wine. For, the Ball of this being put into our frigorifick mixture, the Crimson Liquor will nimbly enough descend much lower, than when it was kept either in the open Air, in common Water, of the same temper with that, wherein the Sal Armoniack was put to dissolve. And if you remove the Glass out of our Mixture into common water, the tincted Spirit will, (as you may remember, it did) hastily enough reascend for a pretty while, according to the greater or lesser time, that it continued in the Armoniack Solution. And this has succeeded with me, when instead of removing the Mixture into Common Water, I removed it into water newly impregnated with Salt-peter.
