:%vo Mr , Walker’s 'Experiments on the 
cold, the temperature of the air and materials before mixing 
being 63°; which is no more than I have found may be effected 
by a folution in water of crude fal ammoniac alone, pre- 
vioufly dried and powdered. 
By a trial made with great accuracy, I find, that even the 
mixture compofed of diluted vitriolic acid and vitriolated na- 
tron is adequate to any ufeful purpofe that may be required in 
the hotted: country ; for, by adding eleven parts of the fait in 
fine powder to eight parts of the vitriolic acid diluted with 
an equal weight of water, the thermometer funk from 8o°, 
the mean temperature of the hotted: climate, and to which 
thefe materials were purpofely heated before mixing, to rather 
below 20 0 . 
Vitriolated natron, added to the marine acid undiluted, pro- 
duces very nearly as great a degree of cold as when mixed with 
the diluted nitrous acid. At the temperature of 50°, two 
parts of the acid, require three parts of the fait in fine pow- 
der, which will fink the thermometer to o° ; and if three parts 
of a mixed powder, containing equal parts of muriated am- 
monia and nitrated kali, be added afterwards, the cold of the 
mixture will be increafed a few degrees more. 
The frigorific mixture above defcribed, compofed of phof- 
phorated natron and nitrated ammonia diffolved in the diluted 
nitrous acid, being the moft powerful, it will probably be 
found moft convenient for freezing mercury, when fnow is 
not to be procured. The materials for this purpofe may be 
previoufly cooled in mixtures made of marine acid with vitri- 
olated natron, muriated ammonia, and nitrated kali, in the 
proportions mentioned above, this being much cheaper than 
thofe made with diluted nitrous acid, and very nearly equal in 
effedt. 
In 
