154 THE LACTATES, AND UREA AS IT EXISTS IN URINE. 
and a slight excess of hydrate of zinc added. The materials 
being thoroughly mixed by agitation, are moderately heated, 
and left for several days. There will then be noticed in the 
mass an abundant precipitate, surmounted by a clear liquid, 
which must be decanted and reserved for future operations. 
The precipitate is lactate of zinc, with an excess of base. It 
is to be boiled with eight times its weight of distilled water, 
and some animal charcoal; filtered while hot, and evaporated 
to form crystalline pellicles, which, being collected and puri- 
fied, are very pure and white lactate of zinc. This salt crys- 
tallizes in fine needles, has an acid, styptic taste, is more solu- 
ble in hot than cold water, scarcely soluble in alcohol, and pre- 
cipitates in white flocculi with alkaline sulphurets. Treated 
with baryta or slacked lime, it is changed into hydrate of zinc, 
and lactate of baryta or of lime. 
The lactate of lime may also be prepared directly from 
sour milk, or rather with the alcoholic liquor resulting from 
the final precipitation of the sugar of milk. This latter liquid 
is to be treated with slacked lime, or a slight excess of chalk, 
heated, filtered while boiling, and evaporated to dryness. The 
residue is a kind of syrupy paste which, when moistened, as- 
sumes a crystalline mamelated appearance ; these crystals are 
to be drained, expressed, and treated with water and charcoal. 
The liquid concentrated and left at rest, becomes filled with 
crystalline tufts, which, dried by bibulous paper, present small 
crystals of a milky whiteness, crackling under the teeth, and 
of a somewhat bitter taste. When heated, it fuses and has a 
resinous appearance, but, on being moistened, does not fail to 
crystallize in the same manner. The lactate of lime is more 
soluble in hot than in cold water ; heated with sulphuric acid, 
a slight effervescence is produced, the mass blackens and gives 
off the odor of the rennette apples. We know that the ace- 
tates treated in the same manner give off acetic acid. 
The lactate of baryta does not crystallize, as MM. Pelouse 
and J. Gay-Lussac have already announced ; it is procured 
under the form of a gummy matter, very soluble in water and 
in alcohol. 
