VOL. XXII.] PHILOSOPHICAL TKANSACTIONS. 6j3 



thing but the diminution of motion ; so that the coldness which the salts bring 

 to the water, seems to be occasioned from this, that the salt particles being 

 without motion, and dividing that liquor, diminish it so much the more. And 

 this is what produces the cold, more or less in the same liquor. 



There is one thing to be observed, which is, that some time after the solu- 

 tion is made, the liquor of the thermometer rises again a little. Which may 

 be occasioned by this, that the subtile matter which glided abundantly between 

 the liquid particles, had ceased to glide there in the same quantity for some 

 time, the gross particles of the salts opposing themselves against their passage; 

 but these saline particles being divided by little and little, they opened again the 

 passage to the subtile matter. This gave the liquor more motion than it had at 

 the beginning of the solution ; but yet less than it had when it was pure, and 

 without mixture ; the saline particles, although dissolved, abating somewhat of 

 their motion. 



We may easily comprehend why lixivious salts, purely alkaline and well cal- 

 cined, as also the salt of tartar, heat the liquor, and are very far from cooling 

 it, if we consider that these salts, in the strong calcination, which they have 

 undergone, are impregnated with many fiery particles, which they hold, as it 

 were in prison, in their pores. These igneous particles regain their liberty by the 

 solution of the saline particles. And in the same time that these salts ought to 

 slacken the motion of the aqueous particles, and cool it, the igneous particles, 

 being very active, augment the agitation of the watery particles, till they make 

 it very hot. 



I observe next, that sal ammoniac cools the water wherein it is dissolved more 

 than any other salt. Its cold equals that of water which is ready to freeze. And 

 it happened once that in dissolving a good quantity of this salt in water, some 

 drops which fell on the outside of the phial, in which I made the solution, 

 froze, and the straw upon which the phial stood being wet, was fastened to the 

 glass vessel for some time by the ice : and this at a time when the weather was 

 warm. 



I often tried the same experiment after in different ways, but without ever 

 being able to produce ice. Chance had apparently made meet in this experi- 

 ment, not only a very exact proportion between the salt and the water, but also 

 a temperature in the water besides, which I suppose necessary: because, the 

 solution being quick, the cold must also be more sudden and great : and this is 

 that degree of temperature to which I could never afterwards attain. 



The great coldness of the solution of sal ammoniac does not proceed from 

 any difficulty it has to be dissolved, since it dissolves sooner than any other. 

 And sea-salt, whose solution is difficult and very slow, is that which least cools 



