278 Mr. Walker's Observations on the 
Whenever the intention is, as in these experiments, to cool 
the materials to nearly the same temperature with the frigo- 
rific mixture in which they are immersed, the proportion of 
the frigorific mixture to the intended mixture (or materials to 
be cooled ) should not be less than twelve to one ; a greater 
disproportion is still better. 
By attending to the directions particularly mentioned in the 
experiment made on Dec. 28th, a thermometer may be always 
dispensed with ; the proportions of the materials to be cooled 
being exactly adjusted ; and when they are to be mixed pre- 
cisely determined, by the time employed in grinding the ice 
to powder. The proportions of snew, or pounded ice, and salt, 
or salts, may be guessed sufficiently near without weighing, 
unless in very nice experiments. 
Imagining that a recapitulation of the different mixtures, 
described in my former paper, for producing artificial cold, 
brought into one view might not be unuseful, I have subjoined 
a Table of the salts, their powers of producing cold with the 
different liquids, and the proportions of each, according to a 
careful repetition of each ; the temperature being 50°. 
