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_.

{258}

2. The _Duration_ of the Cold, produc'd by this Experiment, depends upon
several Circumstances; as _First_, upon the Season of the year, and present
temperature of the Air; For, in Summer and Hot weather the Cold will sooner
decay and expire. _Secondly_, upon the Quantity of Salt and Water: For, if
both these be great, the effect will be as well more lasting, as more
considerable. _Thirdly_, for ought I yet know, we may here add the Goodness
& Fitness of the particular parcel of Salt, that is imploy'd; for, though
it be hard to discern beforehand, which will be the more, and which the
less proper; yet some trials have tempted me to suspect, that there may be
a considerable disparity, as to their fitness to produce Cold, betwixt
parcels of Salt, that are without scruple look't upon as Sal Armoniack: Of
which difference it were not perhaps very difficult to asign probable
reasons from the Nature of the Ingredients of this compound Concrete, and
the wayes of preparing it. But the Duration of the Cold may be conceived to
depend also. _Fourthly_, upon the Way of putting in the Salt into the
Water. For, if you cast it in all at once, the Water will sooner acquire an
intense degree of Coldness, but it will also the sooner return to its
former temper; Whereas, if you desire but an inferiour degree of that
Quality, but that may last longer (which wil usually be the most convenient
for the Cooling of Drinks