412 PHILOSOPHICAL TRANSACTIONS. [anNO 1788. 



first object therefore was, to determine in what manner the property of bearing 

 to be cooled would be affected with regard to that new point of congelation. 

 For this purpose I made many experiments with several different substances, 

 which it would be too long to relate in detail, but the principal were as follows. 



Having dissolved in distilled water as much common salt as lowered its freezing 

 point to 28°, I cooled it to 18°-i- before it congealed. Another solution of the 

 same salt, whose freezing point was 1 6°, bore to be cooled to g° ; and a stronger 

 solution, whose freezing point was 13°4-, cooled to 5° before it shot. A solu- 

 tion of nitre, whose freezing point was 27°, cooled to l6°, that is, ] 1° below 

 its new freezing point ; a solution of sal ammoniac, whose freezing point was 

 12°, cooled to 3°; and one of Rochelle salt, freezing point 27°4^, suffered the 

 thermometer to sink in it to l6° before it froze ; a cooling equal to the greatest 

 I ever obtained with the purest distilled water boiled. A solution of green 

 vitriol, whose freezing point was near 30°, cooled below 19°: and of salts with 

 an earthy basis, a solution of the common bitter purging salt, whose freezing 

 point was at 25%, bore to be cooled to 19°. 



Acids rather augment this quality of being cooled below the freezing point. 

 A combination of nitrous acid with distilled water, in such proportions that the 

 new freezing point was between 18° and 19°, sunk down to 6° before it con- 

 gealed; which being fully 12° of cooling, is greater than I have been able to 

 produce with pure water. Another mixture of the same kind, so strong as to 

 have its freezing point about 11°, cooled down to 1°. A mixture of vitriolic 

 acid and distilled water, whose freezing point was 24^4^, cooled to 14°; and one 

 with the acid of salt, having its freezing point at 25°, sunk to 16° before it 

 froze. It is here to be observed, that these acid mixtures were rather remark- 

 able for the steadiness with which they bore to be cooled, and the little ten- 

 dency they showed to shoot before they were sunk much below the freezing 

 point, than for exceeding the number of degrees which pure water might be 

 cooled. Of the alkalis, a solution of tartar, whose freezing point was 25°-i-, 

 cooled to 18°; and another, with the freezing point at 15°, sunk to 8°. A so- 

 lution of crystallized soda, freezing point 30°, cooled to 21° ; and a solution of 

 mild volatile alkali, freezing point 19°, to 11°. A mixture of rectified spirit of 

 wine and water, whose freezing point was 12°, cooled to 5°; and another, with 

 the freezing point at 8°-i-, to 2°. 



All these facts, with many others of the same nature, sufficiently show, that 

 foreign substances, chemically combined with or dissolved in water, do not take 

 away its property of being cooled below its point of congelation ; though, by 

 depressing that point, they alter the degree of cold at which the property com- 

 mences. The experiments show, that in some cases the mixed water bore to be 

 cooled as much below its new freezing point, as pure water below 32° ; and 



