204 PREPARATION OP LACTIC AND BUTYRIC ACIDS. 
has been removed, are added to the above mixture along 
with 3 lbs. of finely-powdered chalk, the whole located in 
a warm place, so that the temperature of the liquid is from 
86° to 95°. It is well stirred every day several times ; in the 
course of 8 to 10 days the entire mass solidifies to a stiff 
paste of lactate of lime ; 20 lbs. of boiling water and § oz. 
of caustic lime are added to this paste, boiled for half an 
hour, and filtered through a linen bag. The liquid is evapo- 
rated to the consistency of a syrup, set aside for four days, 
in which time the lactate of lime has separated in a granular 
crystalline form ; it is expressed, then agitated with one- 
tenth its weight of cold water, again submitted to pressure, 
and this operation repeated two or three times. 
The lactate of lime, after being expressed as well as 
possible, is dissolved in twice its weight of boiling water ; 
and for every pound of expressed lactate of lime, 3| oz. of 
sulphuric acid previously diluted with its weight of water 
added to the solution. The hot liquid is immediately fil- 
tered through a conical bag from the gypsum, and boiled 
with If lb. of carbonate of zinc for every 1 lb. of sulphuric 
acid used for a quarter of an hour ; if boiled longer, a very in- 
soluble basic salt is formed. The solution, filtered boiling 
hot, soon deposits perfectly colourless lactate of zinc in 
crystalline crusts, which may be obtained perfectly free from 
sulphuric acid by rinsing with cold water. The mother-ley 
is again boiled with any of the salt which may have re- 
mained on the strainer, or concentrated by evaporation. It 
yields, nearly to the last drop, perfectly white zinc salt. 
To separate the lactic acid from this salt, I dissolve it in 
7| parts of boiling water, pass a current of sulphuretted 
hydrogen into the hot liquid until it has become cold, and 
no further separation of sulphuret of zinc is perceptible. 
The liquid filtered from the sulphuret of zinc is boiled to 
expel the excess of sulphuretted hydrogen, and then evapo- 
rated in a water-bath to the consistence of a syrup. 8 parts 
