VOL. LXXVIII.] 



PHILOSOPHICAL TRANSACTIONS. 



465 



Freezing 



point by 



calculation. 



31 



30| 

 28 

 26| 

 25k 



Sal Catharticus Amarus. 

 The common sal catharticus amarus of the shops was the specimen used of an 

 earthy salt. It formed a turbid inelegant solution, as if dirty; and with various 

 proportions of water produced the following points of congelation. 



The 3d column is calculated from the last ex- 

 periment, where the freezing point of a solution 

 of 1 part of the sal catharticus amarus in 2.4 

 of water proved to be 254-°. No salt was de- 

 posited from the strongest of these solutions; 

 and as that here used was a deliquescent salt, it 

 must probably have been in a vast proportion to 

 the water, before any such effect would have 

 taken place. Dr. B. has sunk a thermometer 

 with it and snow to 7°-^; which according to the proportions in the table, would 

 make more than 3 parts of the salt to 1 of water. Accordingly, a large quantity 

 of the salt was required to the snow. No particular phaenomenon was observed 

 with this salt, except the singular configuration of its ice, which assumed the 

 form of fungi, or of some kinds of lichen, with feathered striae. The solutions 

 were difficult to cool much below their freezing point. 



Green PltrioL 

 Of the salts with a metallic basis, green vitriol affords one of the most trans- 

 parent solutions in water. It sinks the thermometer nearly to 274° with snow, 

 and reduced the freezing point of water according to the following table. 



The 3d column is calculated from the last ex- 

 periment, in which the freezing point of a so- 

 lution of 1 part of the green vitriol in 2.4 of 

 water proved to be 28°. The ice formed by 

 these solutions assumed a foliaceous configura- 

 tion, with a texture of penniform striae, in some 

 respects like the appearance exhibited by a drop 

 evaporating under a microscope, as delineated by 

 Baker. Scarcely any salt gave the point of con- 

 gelation so regularly in the proportion of the quantities mixed with the water, 

 and none afforded solutions which cooled more easily and readily below the 

 freezing point. In 2 instances the cooling was more than 1 1^ 



fVhite Fitriol. 



Having found that white vitriol, mixed with snow, produced a cold of 20°, 



melting the snow remarkably fast, I was induced to try the freezing point of its 



solutions. But though it dissolved very readily in water, yet the liquor it 



formed was so turbid and thick, that little satisfaction could be derived from the 



VOL. XVI. 3 O 



