CHEMISTRY. 165 



At Edinburgh, coal gas is manufactured at a total 

 expense of 8*. per 1000 cubic feet, and sold for 12s.; 

 oil gas costs 26s. per 1000 cubic feet in manufac- 

 turing, valuing the oil at 2s. per gallon, but it has 

 almost double the illuminating power of coal gas. 



In 1824, the extent of gas-pipe in and about Lon- 

 don exceeded 900 miles. 



Latent Heat. 



Let one pound of ice at 32 be dissolved in one 

 pound of water at 172, and it will be found that 140 

 of heat have disappeared and become latent in the 

 fluid, which assumes the temperature of 32 only. 



On the other hand, if a pound of water at 1 72 be 

 mixed with a pound of ice-cold water at 32, the 

 temperature of the mixture will be exactly 102, 

 which is the mean of 32 + 172 or 204. 



It requires 1 40 degrees of heat to give it fluidity, 

 which it receives without the least augmentation of 

 temperature perceptible by the thermometer. 



The fire produced by flint and steel is caused by 

 the sudden extrication of the latent caloric. 



Solar and Terrestrial Heat. 



It has been conjectured, that there is a difference 

 between solar and terrestrial heat, the rays of the 

 first passing through glass without heating it, while 

 the rays of the latter are stopped by the glass, which 

 becomes hot when opposed to them, 



Animal Heat. 



It is probable that all organized beings, vegetable 

 as well as animal, possess an inherent power of gene- 

 rating cold or heat according to circumstances. 



Extreme Heat of the Air. 

 We may conclude, from some experiments of 



