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Mr. Walker’s Experiments on 
in the vessel B, and the vessel covered by its lid D, then set 
upright, and four drams of muriate of lime put into the cup b. 
3d. A similar frigorific mixture is made in the vessel A A, 
which is closed with its lid C. 4th. This vessel being placed 
over the other, as represented, three drams of water are to be 
poured gently, through a funnel, into the tube a, and the aperture 
closed. 5th. When the water is become perfectly solid ice,* 
the grinding instrument is to be putin, and, after suffering it to 
remain a short time to be cooled, the ice is to be ground gently 
to fine powder, (an assistant holding the apparatus firm,) and the 
instrument continued quite through the aperture at the bottom 
of the tube. fith. The whole of the ice-powder is then to be 
for 1795. The mixture I use for this purpose, is that consisting of the solution of three 
different salts in water; and, in order to ascertain what proportions may be necessary to 
fill any sized vessel, I shall give the proportional quantities for a vessel containing in 
measure a wine pint, which are as follows: of muriate of ammonia 3 ounces, nitrate 
of potash 3 ounces, sulphate of soda 4 ounces and f, and water 10 ounces : having pro- 
cured the salts separately in fine powder, I put these first into the vessel, and then fill 
up (without measuring) the vessel with water. 
A mixture of this kind, made in the summer, when the temperature of the air is 
-}- 70°, will cool the materials to -f zo ° ; and, if the salts and water are cooled to near 
-f 50°, previously to mixing, by immersion in cold water, to -j- io°. My usual method 
is, (without taking the usual precaution of cooling the salts,) to add the water much 
reduced in temperature, by pumping off a bucket or more first, by which the materials, 
consisting of muriate of lime and ice, are cooled to -4 15 0 before mixing. 
In winter, the experiment may be conducted by adding snow, at the temperature of 
the air, to muriate of lime, (cooled toalower temperature,) in the vessel B. In summer, 
by adding ice-powder, cooled to a low temperature, in the vessel A, to muriate of lime 
cooled to 50°, by water, (instead of a frigorific mixture,) in the vessel B. 
The temperature of the springs, or of well-water, it is well known, is in this climate 
nearly -f 50° throughout the year. 
• At this period, I shake the apparatus, in order to expedite the solution of the 
salts, and to diffuse the effects of the freezing mixtures ; or, if necessary, renew 
them. 
