HEAT OR CALORIC. 12.; 



trate of ammonia, 28 ; muriate of lime three parts, and water two, 

 37 ; muriate of ammonia, and nitre in powder, with from five to 

 eight parts of water, from 50 to 11 ; and the salts, recovered by 

 evaporation, answer as well as before. 



Diluted acids with salts, are more powerful than water only. Sul- 

 phate of soda, with sulphuric acid, diluted with as much water, re- 

 duces the temperature from 50 to 5, and with diluted nitric acid, 

 from 51 to 1. With mixed salts the cold is still greater. Phos- 

 phate of soda, nitrate of ammonia, and diluted nitric acid, reduce the 

 thermometer from 50 to 21, and mercury has been frozen by a 

 mixture of nitrous acid, sulphate of soda, and nitrate of ammonia.* 

 By these, or similar means, all fluids have been frozen, except al- 

 cohol, and several of the gases have, by the aid of strong pressure, 

 been condensed into fluids. 



The salts should be previously well crystallized, and should retain 

 their full proportion of water ; they should be well pulverized ; they 

 should be mixed in vessels which are bad conductors of heat ; 

 the access of the external air should, as much as possible be cut ofF, 

 and the materials may be previously cooled by being placed sepa- 

 rately in other freezing mixtures, taking care that they be not cooled 

 below that degree at which the materials act on each other.f 



(m.) Many heat-producing , or calorific mixtures, act by diminu- 

 tion of capacity.-. Sulphuric acid and water combine with increase 

 of specific gravity, and diminution of specific heat, and therefore 

 with increase of sensible heat. 



Many other acids, e. g. the nitric, muriatic, fluoric, &tc. act in the 

 same way ; even alcohol and water, in considerable quantities, grow- 

 sensibly warm by being mixed. The heat evolved in those cases 

 in which the products of the chemical action are chiefly gaseous, does 

 not appear to be well accounted for in this way. Nitric acid and oils, 

 gunpowder and fulminating compositions generally, and mixtures of 

 the chlorates with the combustibles, result in the conversion, more or 

 less, of solids into aerial matter, and cold should therefore be genera- 

 ted, instead of heat, which is always evolved in great quantities. 



Dr. Turner sums up our knowledge of specific heat under the fol- 

 lowing heads. 



1. " Every substance has a specific caloric peculiar to itself, 

 whence it follows that a change of composition will be attended by a 

 change of capacity for caloric." 



2. "A change of form, the composition remaining the same, is 

 likewise attended with a change of capacity. It is increased when a 

 solid liquifies, and diminished when a fluid passes into a solid." 



3. " It is certain that the specific caloric of all gases increases as 

 their density diminishes, and vice versa. 



* Graham. * Murray. 



