42 



HEAT. 



of 7; the ice-glass, after being exposed 

 twenty-one half hours, attained the same 

 temperature. It is obvious that the ice- 



glass must have received, during every 

 alf hour, nearly the same quantity of 

 heat which the water-glass did, while 

 its temperature was being raised 7; 

 so that the whole quantity of heat im- 

 parted to the ice-glass will be found by 

 multiplying 21 by 7, or 147. In other 

 words, the quantity of heat received by 

 the ice-glass would have raised the tem- 

 perature of water 147, but only eight 

 degrees of this quantity were to be de- 

 tected in the water by a thermometer ; 

 consequently the remaining 139 or 140 

 must have been absorbed to enable the 

 ice to liquefy. 



Another method of ascertaining the 

 same thing occurred to Dr. Black, by 

 submitting ice to the action of warm 

 water. Having prepared a piece of ice 

 of a shape fit for his purpose, and 

 weighing 59 drachms, he plunged 1 it 

 into a quantity of water at the tempe- 

 rature of 190, weighing 67 drachms; 

 the whole of the ice was liquefied in a 

 few seconds, and the temperature of the 

 fluid was immediately found to be 53. 

 Thus the heat of the water used in this 

 experiment was reduced from 190 to 

 53, as was the glass vessel which con- 

 tained the "water : it had been previ- 

 ously ascertained that the power of the 

 vessel to heat bodies was not more than 

 half that of water ; the weight of the 

 vessel was eight drachms, but on ac- 

 count of its less power of heating, the 

 eight drachms are taken in the calcula- 

 tion as four of water. The tempera- 

 ture of 67^ drachms of water, together 

 with four drachms of water capable of 

 exerting the same heating power, was 

 reduced, in this experiment, 137; the 

 whole of which quantity being commu- 

 nicated to 59i drachms of ice, at 32, 

 raised its temperature only 21; al- 

 though, according to the relative pro- 

 portions of hot and cold matter, it ought 

 to have elevated the temperature of the 

 ice 86. A quantity of heat, therefore, 

 was suddenly lost, equal to 65, which, 

 it was calculated, would have been 

 sufficient to have raised the temperature 

 of a quantity of water equal in weight 

 to the ice 143. 



Dr. Black simplified the experiment 

 by putting a lump of ice into an equal 

 weight of water at 1 76 ; the ice was 

 melted, and the temperature of the 

 whole was reduced to 32. 



Ex. This experiment will succeed 



more satisfactorily, if to a pound of new- 

 fallen snow we add a pound of water 

 at 172; 'the snow will be liquefied, 

 and 32 will be the resulting tempera- 

 ture. 



Thus it appears that heat entering 

 into bodies enables them to assume the 

 fluid state by counteracting in some 

 degree the influence of cohesive attrac- 

 tion, which holds the particles together, 

 repelling them to greater distances, and 

 permitting them to have freedom of 

 motion among each other. It is be- 

 lieved, however, that something more 

 is necessary to this freedom of motion 

 than weakness of cohesive attraction. 

 Professor Robison supposed, that while 

 a substance remains in the solid state, 

 the particles attract each other more 

 strongly in one direction than another, 

 on which account they will assume par- 

 ticular positions, and oppose more or 

 less resistance to any force tending to 

 change these positions ; but when these 

 particles enter into the fluid state, it is 

 supposed that they attract each other 

 equally in all directions, which would 

 enable them to move with the smallest 

 impulse, although the attraction between 

 them should scarcely be diminished in 

 force. 



It has often been asserted, that a 

 state of solidity is the natural state of 

 all bodies : but the propriety of this 

 assertion is doubtful, as examples might 

 easily be adduced of substances which 

 continue in different states according to 

 the heat of the climate in which they 

 may happen to be placed : thus sulphu- 

 ric ether, which is permanently liquid in 

 this climate, would always remain solid 

 in the coldest parts of the arctic regions ; 

 and the state of elastic gas would be 

 the only state in which it could exist 

 near the Equator. 



Fluidity. 



All liquids, with the exception of al- 

 cohol, have been reduced to the solid 

 state ; and it is generally believed that 

 this also would become solid if we were 

 able to reduce its temperature suffici- 

 ently: the same opinion is entertained 

 respecting elastic fluids. All solids that 

 do not suffer decomposition at low tem- 

 peratures may be converted into fluids, 

 and most of them into vapour, by the 

 intense heats produced by modern inge- 

 nuity. When bodies that remain fluid 

 at the usual temperature of the air 

 become solid, we say they are frozen ; 



