^ PHILOSOPHICAL TRANSACTIONS. [aNNO 1757. 



off, they can be no longer supported in the fluid, but must be precipitated by 

 the force of their own gravity. 



Exper. 12. When the water was exposed for some days to the air, there was 

 a cremor separated from it of a shining chalybeate colour. This, like other kinds 

 of cremor, takes a considerable time to complete its entire separation from the 

 fluid, out of which it is expelled : for when it was despumated, a new cremor 

 always succeeded, till the whole quantity, which the water contained, was ex- 

 hausted. 13. When this cremor first appeared on the water, it was of a faint 

 bluish colour : but as it increased, it changed into a deeper and more bright 

 shining blue : and after longer standing it became blotched with various colours, 

 as red, orange, yellow, green, blue, purple, and violet. 14. A quantity of the 

 water being put in a gentle heat, this cremor was quickly separated from it, and 

 appeared on the surface of the water. A like quantity of the water, with its 

 cremor already on its surface, was put over a gentle heat, which by degrees broke 

 the cremor into very small parts ; but whether they evaporated or precipitated in 

 the water, he could not be certain. But, by other trials, this cremor was found 

 to have a great degree of fixity, bearing a considerable heat without avolation ; 

 yet not without the appearance of some of its parts flying ofl^ though most of 

 them were fixed ; because what remained lost its fine colours, and was changed 

 into a shining chalybeate colour. 15. The water of the lower spring afl<:)rded a 

 much less quantity of the cremor than the water of the upper spring. It took 

 also a longer time to separate, was of a bluish colour, and had not the vivid 

 colours which the water of the upper spring showed. l6. When ol. tart. p. d. 

 and spirit of sal ammoniac were added to the water, it did not separate its 

 cremor. 



This cremor, which is separated from the water, is the same as appears on the 

 surface of a solution of vitriolum martis, when exposed for some time to the air : 

 and an infusion of iron in common water also emits a cremor of the same kind. 

 As he was once carefully observing a large glass full of a chalybeate-water, which 

 contained much of this cremor ; soon after it was exposed to the air, he observed 

 a tenuious bluish vapour rising in the parts of the water next the surface, which 

 very much diminished its transparency ; and by degrees this vapour was emitted 

 by the lowest parts of the water : but as the cremor increased on its surface, the 

 water became gradually deprived of the bluish tincture, which it received from 

 this halituous body ; which was apparently nothing else but the parts of the 

 cremor separating from the water, and ascending upwards. Whence we may 

 conclude, that this cremor consists of the very finest parts of iron attenuated to 

 the highest degree. 



The next trials were in quest of alum. 



Exper. 17. A quantity of the water being kept for some time in a boiling 



