JOS PHILOSOPHICAL TRANSACTIOyS. [anNO 1684-5. 



well at Knaresborough, that is, of natural brine evaporated to the same height 

 with the sea water. The 4th, in the morning, the solution of nitrum mura- 

 rium half of it ice ; but not any of the rest. The 6th, in the morning, the 

 bottle of nitrum murarium was most ice. The sulphur water had no ice that I 

 could perceive at all in it : the natron had much ice at the bottom of the 

 bottle; and the Scarborough sea water had some flakes of ice. The icicles of 

 the natron were prettily figured, as is represented in fig. 5, pi. 3 : the icicles of the 

 sea water were also figured in oblong squares, as in fig. 6, and were brittle and 

 transparent. I set the drained icicles of natron before the fire, when it readily 

 enough dissolved into water again ; this ice was both alike salt in ice and in 

 water, much like in taste to the water out of which it was frozen. In like 

 manner having drained the sea water ice, and exposed it before the fire; these 

 icicles became soft and moist by degrees, but at length rather evaporated, than 

 quite melted away; and having taken up a good thick lump of common ice, at 

 least 100 times their thickness and bulk, this in a few moments at the same 

 distance before the fire, grew always moisture, and dissolved into water; whereas 

 the salt icicles, after 3 quarters of an hour lying before the fire, at length dried 

 into a white powder, which was perfect salt, the moisture totally evaporating. 

 Also the sea water icicles tasted very salt, when first taken out of the water. 

 I repeated the same experiment of exposing to freeze the bottles of natural 

 brine of Knaresborough sulphur, full half evaporated, and the same former 

 Scarborough sea water, the 7th and 8th instant at night, and with the like 

 success, viz. no icicles in the natural brine, but the same large ones as above 

 described in the sea water, but not till after the 2d night's keen freezing. These 

 salt icicles continued unthawed in the bottles, though they were brought into 

 the house, and kept in a warm room, long after all other ice within doors was 

 gone, viz. till the 1 '2th instant at night, when the icicles also were dissolved. 

 From which experiments we note, 1 . That there may be salt ice from sea water 

 frozen. 2. That there is a real difference between natural brine and sea water; 

 as there is between the salts themselves, which they yield. 3. That the great 

 floating mountains of ice in the northern seas, if on strict trial they shall be 

 found to be salt, are not only the effects of many years freezing, but also much 

 of their magnitude may be owing to the natural duration of that sort of ice. 

 As to the nitre of Egypt, which the experiments made about it at Oxford 

 plainly show to be little different from sal ammoniac ;* considering that it rains 

 little or nothing comparatively to the great heats in that country ; and that the 

 lakes there ace only once a year furnished with fresh water from the over- 

 flowings of the Nile ; also that vast tracts of land there, and all over Asia, are 



* This conclusion is erroneous. See p. 51, of this vol. of these abridgements. 



