6l4 PHILOSOPHICAL TRANSACTIONS. [aNNO 1701. 



its dissolvent. On the contrary, it seems that the facility and readiness with 

 which it dissolves, may be the very cause of this great cold, in this manner. 



Sal ammoniac, as every one knows, is a composition of sea-salt * and salt of 

 urine; -|- the one very easy, the other very hard to dissolve ; the particles of sea- 

 salt being imprisoned among the particles of the salt of urine, it happens that 

 many of the aqueous particles, at first penetrating the saline particles of the 

 urine, do there immediately lose much of their motion : and this motion grows 

 weaker by so much the more, as the aqueous particles meet afterwards with sa- 

 line particles of another nature, whose resistance is much more considerable, 

 than that of the salts of urine. So in the first instance of the solution, the 

 motion of a great quantity of aqueous particles being very much abated all at 

 once, by the salts of urine, and by the sea salt, it excited in a few moments a 

 cold far greater than the cold of other solutions of salts, which water does not 

 penetrate so readily. 



It may be objected, that the sea-salt being the hardest to dissolve, its so- 

 lution should also be the coldest. To which I answer, that this might be, if the 

 water could penetrate suddenly into all its parts : but the slowness with which it 

 penetrates them, because of the close texture of the molecules of this salt, 

 prevents the diminution of the motion of the parts of the water from being so 

 ready, and by consequence so great; whereas in sal ammoniac, the parts of 

 the sea-salt being extended by the salt of urine, the pores of the alkaline salt of 

 urine are like so many passages, open to the parts of the water, in order to pe- 

 netrate the parts of the sea-salt in numberless places. 



I place in the rank of cold solutions, an experiment made by M. Romberg, 

 which serves to prove what I am going to say about the cold of sal ammoniac. 

 It is made thus : Take a pound of corrosive sublimate, and a pound of sal am- 

 moniac, and powder them each apart ; then mix both the powders very exactly ; 

 put the mixture into a phial, pouring upon it a pint and half of distilled vinegar, 

 shaking it well together. This composition will be so very cold, that a man can 

 hardly hold the vessel in his hands in summer. And it happened as M. Romberg 

 was making this mixture, that the mixture froze. In this experiment we see a 

 cold still greater than that in the solution of sal ammoniac alone in common 

 water. And this cold is caused by the corrosive sublimate, which alone is not at 

 all, or at least very little soluble in distilled vinegar. So that the fluid parts of 

 the distilled vinegar having quickly penetrated the parts of the sal ammoniac, and 

 having already lost a great deal of their motion, engaging afterwards in the 

 pores of a body which they could not dissolve, and having action not more than 



• Of the acid of sea-salt, f By salt of urine (i. e. of putrid xjrine) the author here means vol. alkali.* 



