Slaked lime is soluble in water at 60° F. (15° C.), to the extent of 1 part in 778. Unlike most substances, it decreases in solubility at higher temperatures, requiring 972 parts of water at 130° F. (54° C.), and 1270 parts at 212° F. (100° C.). Its action upon animal tissues increases rapidly, however, with temperature, though no doubt it is moderated to some extent by the lessened solubility. Calculating from Dalton's numbers, pure lime-water at 60° F. (15° C.) contains 1·285 _grm._[R] of CaO per _litre_, and should require 459 _c.c._ of decinormal acid to neutralise it. This estimate in some cases appears to be slightly too high; e. g. a saturated lime-water from Carboniferous limestone at 56.5° F. (13° C.) required only 433 _c.c._ of decinormal acid, which equals 1·211 _grm._ of CaO per _litre_, and this lime-water, kept with excess of lime, gave nearly constant results for many months together. A magnesian limestone lime-water tested at the same time required 472 _c.c._ of decinormal acid, confirming the old observation of tanners, that such lime is stronger than that made either from chalk or carboniferous limestone. This increased strength must arise from the presence of some soluble base other than lime, and may be due to the magnesia, which, however, is very slightly soluble. Magnesian limestone contains a very large amount of magnesia, and hence would not go so far as a purer limestone; but as a very large proportion of the lime ordinarily used is thrown away undissolved, this is perhaps of little practical moment. (For the chemical examination of limes, see p. 102). [Footnote R: 1 _grm._ per _litre_ is very approximately equal to 1 oz. per cub. ft.]