§§ 222, 223. LACTIC AND GLYCOLIC ACID. 233 



shaking the aqueous liquid Avith ether. On evaporating the 

 ethereal solution, it is obtained in the form of a syrup, easily 

 soluble in water and in alcohol. Both the calcium and lead salts 

 are freely dissolved by water, the former requiring about 10 parts 

 at the ordinary temperature. Lactic acid can thus be separated 

 from many other acids by precipitation with acetate, or, if free 

 acids are present, by digestion with carbonate of lead or calcium. 

 Lactate of calcium is further soluble in boiling 85 per cent, spirit, 

 and crystallizes from hot saturated spirituous and aqueous solu- 

 tions on cooling. 



From a spirituous solution of lactate of lime ether throws down 

 an amorphous precipitate, which gradually becomes crystalline.^ 



The magnesium and zinc salts are also crystalline ; the former 

 is best prepared by precipitating a concentrated solution of lactate 

 of soda with chloride of magnesium in the presence of alcohol ; 

 the latter is frequently of use in detecting lactic acid. Lactate 

 of magnesium requires about 30 parts of cold water for solution, 

 of zinc about 60 ; both are far more easily soluble in hot water. 

 If the presence of lactic acid is suspected, the aqueous solution 

 should be concentrated, digested hot with oxide of zinc, cooled, 

 and examined imder the microscope. It should show bundles of 

 needles and sphjerocrystalline masses, as well as four-sided prisms 

 and wedge-shaped crystals. Paralactate (sarcolactate) of zinc is 

 much more easily soluble, requiring only about 6 parts of cold 

 water. Acicular crystals are also obtained if carbonate of silver 

 is used instead of oxide of zinc ; they are soluble in alcohol. 



Air-dry lactate of calcium contains 29-2 per cent, of water and 

 1 8 "3 per cent, of oxide of calcium. 



The zinc-salt contains 18 '2 per cent, of water and 27 '3 per 

 cent, of oxide of zinc. 



§ 223. Gli/colic Acid. — Gly colic acid is homologous with lactic 

 acid, and resembles it in many of its properties. It has been 

 found in the juice of unripe grapes. Ethereal solutions yield the 

 acid in crystals which melt at 7S° to 79°, and are partially 

 volatile in the vapour of water without decomposition. Glycolate 

 of barium dissolves in 7 '9 parts of cold water, of calcium in 80 "8, 

 of zinc in 31'6, of lead (normal salt) in 31-17. The last three 

 can be obtained in crystals. The precipitate produced by basic 

 acetate of lead is very sparingly soluble (about 1 in 10,000), and 



^ Compare Barfoed, loc. c'lt. 144. 



