88 THE LACTIC ACID GROUP. 



Lactate of copper formed with the a lactic acid crystallises in 

 hard, light blue, warty masses, dissolves in T95 parts of cold and 

 1*24 of hot water, and very readily in alcohol; at 100 it begins 

 slowly to lose a portion of its water, and at 140 it decomposes, 

 with a separation of suboxide of copper. Lactate of copper formed 

 with the b lactic acid, with 2 atoms of water of crystallisation, occurs 

 in much larger crystals of a dark blue or green tint ; it dissolves in 

 6 parts of cold and 2*2 of boiling water, in 115 parts of cold and 26 

 of boiling alcohol ; it parts with its water very readily and per- 

 fectly, both at 100, and in vacuo, and does not become decom- 

 posed at a temperature lower than 200, when it inflames and 

 smoulders. 



Basic lactate of protoxide of tin, 2SnO. La, is a crystalline, 

 anhydrous powder, which is very insoluble in water, and absolutely 

 so in alcohol, 



Lactate of suboxide of mercury, Hg 2 O. La + 2HO, forms red 

 crystals which are difficult of solution, and which, on boiling, become 

 decomposed into a salt of the oxide, and into metallic mercury. 



Basic lactate of protoxide of mercury, 2HgO.La, forms anhy- 

 drous glistening prisms, difficult of solution. 



Lactate of silver, AgO. La + 2HO, occurs in needles of a silky, 

 glistening appearance, which blacken when exposed to light. This 

 salt is almost insoluble in cold, but dissolves very readily in hot 

 alcohol; it decomposes at 100; the aqueous solution, when boiled 

 gradually, assumes a blue tint and deposits brown flocculi. 



Products of its metamorphosis. Lactide, C 6 H 4 O 4 , On heat- 

 ing the ordinary, colourless, hydrated lactic acid to 130, water and 

 a little lactic acid distil over, whilst there remains a yellowish white 

 solid substance, which is very fusible, very bitter, almost insoluble 

 in water, but dissolves readily in alcohol and ether, and whose com- 

 position is expressed by the formula, C 6 H 5 O 5 . This product, when 

 boiled with water, or for a long time exposed to the atmosphere, 

 becomes again converted into ordinary hydrated lactic acid, and 

 with milk of lime it yields the ordinary lactate of lime (Pelouze*.) 

 If, however, either this so-called anhydrous acid or the hydrated 

 lactic acid be heated to 250, the products of decomposition are 

 carbonic acid, carbonic oxide, lactide and lactone, but no carbo- 

 hydrogen. The lactide occurs as a sublimate which must be puri- 

 fied by solution in boiling alcohol. It crystallises from this fluid 

 Jn white tablets which fuse at 107 and volatilise at 250 ; the fused 

 * Compt. rend. T. 19, p, 1219-1227. 



