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ter of an hour it began manifestly to freeze the vapours and drops of water on the outside of the Glass. And when the frigorifick power was arriv'd at the height, I several times found, that water, thinly plac'd on the outside, whilst the mixture within was nimbly stirr'd up and down, would freeze in a quarter of a minute (by a Minute-watch.) At about 34 of an hour after the infrigidating Body was put in; the Thermoscope, that had been taken out a while before, and yet was risen but to the lowest freezing mark, being again put in the liquor, fell an inch beneath the mark. At about 212 houres from the first Solution of the Salt I found the tincted liquor to be in the midst between the freezing marks, whereof the one was at 512 inches (at which height when the Tincture rested, it would usually be, some, though but a small, Frost abroad;) and the other at 434 inches; which was the height, to which strong and durable Frosts had reduced the liquor in the Winter. At 3. hours after the beginning of the Operation, I found not the Crimson-liquor higher than the upper Freezing mark newly mention'd; after which, it continued to rise very slowly for about an hour longer, beyond which time I had not occasion to observe it.
Thus far the Note-book; wherein there is mention made of a Circumstance of some former Experiments of the like kind, which I remember was very conspicuous in this newly recited. For, the frigorifick mixture having been made in a Glass body (as they call it) with a large and flattish bottom, a quantity of water, which I (purposely) spilt upon the Table, was by the operation of the mixture within the Glass, made to freeze, and that strongly enough, the bottom of the Cucurbite to the Table; that stagnant liquor being turn'd into solid Ice, that continued a considerable while unthaw'd away, and was in some places about the thickness of a half Crown piece.
Another Observation, made the same Spring, but less solemn, as meant chiefly to shew the Duration of Cold in a high degree, is recorded in these terms: The first time, the Seal'd Weather-glass was put in, before it touch'd the common water, it flood at 818, having been left there a considerable while, and once or twice agitated the water, the tincted liquor sunk but to 718, or at furthest,768; then the frigorifick liquor being put into the water with circumstances disadvantagious enough, in (about) half a quarter of an hour the tincted liquor fell beneath 334; and the Thermoscope, being taken out, and then put in again, an hour after the water had been first infrigidated subsided beneath 5 inches, and consequently within 14 of an inch of the mark of the strongly freezing weather.
7. Whereas the grand thing, that is like to keep this Experiment from being as generally Useful, as perhaps it will prove Luciferous, is the Dearness of Sal Armoniack; two things may he offered to lessen this inconvenience. For first, Sal Armoniack might be made much cheaper, if instead of fetching it beyond-sea, our Country-men made it here at home; (which it may easily be, and I am ready to give you the Receipt, which is no great Secret.) But next, I considered, that probably the infrigidating vertue of our mixture might depend upon the peculiar Texture of the Sal Armoniack whereby, whilest the Water is dissolving it, either some Frigorifick particles are extricated and excited, or (rather) some particles, which did before more agitate the minute parts of the water, are expell'd (or invited out by the ambient Bodies) or
