Production of artificial Cold. 401 
than I thought neceflary to cool the water to the fame tempe- 
rature; and by repeated trials I found it was neceflary to lower 
the temperature of the mixture to near -f 5 0 , to make the 
water in either of them freeze. Thefe were likewife ful- 
pended out of doors, clofe to a thermometer, during the late 
froft, and the water never obferved frozen. On March the 
22d, at fix in the morning, the water in each remained un- 
frozen, though the tubes were gently fhaken, the thermo- 
meter {landing at that time at 23 0 . There appeared to be little 
difference with refpedt to the degree of cold neceflary to freeze 
the water, whether the tube of the thermometers were open 
or clofed in vacuo (which was very nearly effe£led by buffering 
the water to boil up to the orifice of the tube, and then fuddenly 
fealing it) or not, but unboiled water in the fame fituatiou 
froze in a higher temperature. 
It' is commonly (uppofed, I believe, that gentle agitation of 
any kind will difpofe water (cooled below its freezing point) 
to become ice ; but I have repeatedly cooled rain-water and 
pump- water, boiled a long time, and unboiled, in open veflels 
to 30° or lower, and have conflantly fucceeded, after trying 
other kinds of agitation in vain, by flirring, or rather fcraping 
gently, the bottom and fides of the veflel containing the wa- 
ter to be frozen, when after fome fhort time lmall filaments of 
ice appeared, and by continuing this motion about every part of 
the vtfl’el beneath the furface of the water, about two-thirds 
of the water commonly froze* A (lender, pointed glafs rod I 
tj fed for this purpofe. 
I have the honour to be, See. 
RICH. WALKER. 
Oxford, March 27, 1788. 
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