best Methods of producing artificial Cold. 285 
If it be required to mix the powdered salts and acids at 
a low ■ temperature, the best method is this : put first the 
nitrous ammoniac into the tube of such an apparatus as fig. 1. 
shaking it down level, gently pressing the upper surface 
smooth ; then the phosphorated soda or Glauber's salt ; cover 
this with a circular piece of writing paper, and pour a little 
melted white wax upon it, and when cold, pour upon this the 
diluted nitrous acid; immerse this in a frigorific mixture till it 
is 'sufficiently cold, as found by dipping the thermometer into 
the liquor occasionally ; force a communication through, and 
stir the whole thoroughly together, contriving that the upper 
stratum of salt, that is, the phosphorated soda or Glauber's 
salt, be mixed with the liquor first, and then the nitrous am- 
moniac; the powdered salts do not require stirring whilst 
cooling, like snow, for however hard they are frozen, they will 
readily dissolve in the acid ; care must be taken that the par- 
tition be perfect between the salts and the liquor ; and that in 
this, and every instance where the materials are to be cooled, 
they be immersed below the surface of the frigorific mixture. 
The strength of the red fuming nitrous acid used in these 
experiments, I found to be 1,510, and that of the vitriolic acid 
1,8458. 
I have thought it better, for the sake of brevity, not to use 
in this, as in my former papers, the new chemical names, es- 
pecially as the old ones are more generally known. 
These experiments were chiefly made in a warm room, not 
far from the fire side. 
I have now finished my proposed plan respecting the best ' 
modes of conducting experiments on cold, in which it will 
appear, that I have reduced the congelation of quicksilver, in 
MDCCXCV. P p 
