Volltext: The Works of Robert Whytt

In which lime-water, thus expofed, lofes its virtue, will be more or 
lefs, according to the proportion which the furface bears to the 
quantity of the fluid. 
The fcum which lime-water, expofed to the air, throws up, is at 
firft an extremely thin pellicle, exhibiting various colours like a 
rainbow, or foap-bubble ; thefe colours, however, gradually change, 
till, by the confiant appofition of new particles, the fcum becomes 
thick enough to reflect all the rays of light equally, and fo appears 
Th is cruft which lime-water affords, being well beat, and mixed 
with fyrup of violets, and then fome common water added to it, 
the mixture, after Handing a little, acquires a green colour. The 
parts of this fcum are fo minutely divided, and intimately mixed 
with the water when it is firft poured off the lime, as to be abfo- 
lutely invifible, and to remain infeparable from it, as long as it is 
kept in a clofe veflel. Why they fhould immediately begin to fepa- 
rate from the water, and .unite together when expofed to the 
open air, may not be eafy to account for. But is not lime-water 
rendered weaker by boiling, becaufe its parts are thus more ex¬ 
pofed to the air, and not by the heat’s expelling any thing out 
of it? And does not lime-water, when diftilled in clofe veffels, 
lofe fome of its virtue, becaufe its parts, when elevated in the 
form of a vapour, are more expofed to the aftion of the air 
in the retort and receiver? Is not this rendered probable by Dr 
Black’s obfervation, viz. That though magnefia alba which a- 
bounds with air, deftroys the virtues of quick-lime and its water, 
yet, after it is deprived of its latent air by calcination, it has no 
fuch effetft * ? 
58. The calcarious matter which feparates from lime-water upon 
Its being expofed to the air, can by no art be again diffolved in wa¬ 
ter, or intimately united with its particles, but perpetually falls to 
the bottom, in the form of a white powder, which is altogether 
infipid, and void of tafte. 
ßbb (1.) This 
f DiiTertatio inauguralis, Dc magnefia alba,p. 31. 32. 33, and 37.


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