49 



the excess of the heats of the mixture above that of the cold water should be to 

 the difference of heats of the hot & cold water, as the weight of the hot wa- 

 ter to that of the mixture. 



P. 4. But before we proceed to compare this experiment with the rule it 

 was intended to examine, it is necessary to make some corrections. 



P. 12. Sect. 2. One would naturally imagine that if cold quicksilver, or any 

 other substance, is added to hot water, the heat of the mixture would be the 

 same as if an equal quantity of water of the same degree of heat had been added ; 

 or in other words, that all bodies heat & cool each other, when mixed together 

 equally, in proportion to their weights ; the following experiments however will 

 shew that this is very far from being the case. 



P. 26. It should seem therefore to be a constant rule, that when the effects 

 of any two bodies in cooling one substance are found to bear a certain pro- 

 portion to each other, that their effects in heating & cooling any other sub- 

 stance will bear the same proportion to each other. 



P. 27. The true explanation of these phenomena seems to be, that it requires 

 a greater quantity of heat to raise the heat of some bodies a given number of 

 degrees by the thermometer than it does to raise other bodies the same num- 

 ber of degrees. 



PART II. 



P. 33. As far as I can perceive, it seems a constant rule in nature, that 

 all bodies, in changing from a solid to a fluid state, or from a non-elastic 

 state to the state of an elastic fluid, generate cold, and by the contrary changes 

 they generate heat. I shall first consider those cases in which bodies are 

 changed from a non-elastic to an elastic state, or from an elastic to a non- 

 elastic state, & afterwards those in which they are changed from a fluid state, 

 or the contrary. 



The reason of this phenomenon seems to be, that it requires a greater quan- 

 tity of heat to make bodies shew the same heat by the thermometer, when in 

 a fluid, than in a solid state, & when in an elastic, than in a non-elastic, state. 

 It is plain that, according to this explanation, all bodies should generate as 

 much cold in changing from a soUd, as they generate heat by the contrary 

 change, which as far as I can perceive seems to be the case. 



P. 40. I have been informed that Dr. Black has observed that in distilling 

 water, the water in the worm-tub is heated thereby much more than it would 

 be by mixing with it a quantity of boiling water equal to that which passes 

 through the worm. Upon this principle I made some experiments to deter- 

 mine how much heat is generated by converting water from the state of an 

 elastic to that of a non-elastic fluid. 



P. 43. Experiments to shew that bodies in changing from a solid state to a 

 fluid state produce cold, & in changing from a fluid to a solid state produce 

 heat. — 



P. 45. I made some experiments to determine the quantity of cold produced 

 by mixing snow with the following substances, namely, a solution of sea-salt, 

 pearl ashes, spirit of wine, & aqua fortis. The quantity of cold generated was 

 not very different from that pioduced by dissolving snow in warm water. I 



