84 ORGANIC CONSTITUENTS. 



ammoiiiacal vapour. In water it is perfectly insoluble, in liot 

 alcohol of '833 it is only sliglitly soluble^ and separates on cool- 

 ing into its original flocculeut appearance, since cold alcohol 

 exerts no solvent influence over it. It dissolves readily in ether. 

 It does not form a soap with caustic potash. Lecanu describes 

 the serolin obtained from human serum, as a white, but not 

 nacreous, substance, which melts at 95°, is soluble in ether, but 

 not in watery alcohol. 



It may be distinguished from other fats by its insolubility in 

 cold alcohol ; from cholesterin, by its lower point of fusion. 



Diagnosis. The difi'erent fats and fatty acids are distin- 

 guished by their fusing points, and by their varying degrees of 

 solubility in alcohol and ether. 



Lactic, Oxalic, and Acetic Acids. 



1 . Lactic acid is regarded by most chemists as a constituent 

 of almost all the fluids of the animal body. 



The following is the method recommended by Mitscherlich,^ 

 for the exhibition of pure lactic acid. Sour whey must be 

 evaporated to about one sixth of its volume, and filtered ; the 

 phosphoric acid precipitated by lime, and any excess of lime 

 separated by oxalic acid. 



After filtration, the liquid must be evaporated to the consis- 

 tence of a thick syrup, and the lactic acid extracted with 

 alcohol. The alcohol must be removed by evaporation, and the 

 residue dissolved in water mixed with carbonate of lead. In 

 this manner a solution of lactate of lead is obtained, which, 

 after filtration, must be decomposed by sulphate of zinc. 

 Sulphate of lead is immediately precipitated, and lactate of 

 zinc remains in the solution, which must be filtered and evapo- 

 rated to incipient crystallization. In this manner we obtain 

 crystals of lactate of zinc, a salt only slightly soluble in cold 

 water. Lactic acid mav be obtained bv converting- the lactate 

 of zinc into a lactate of lime or baryta, carefully removing the 

 base by the addition of sulphuric acid, and cautious evaporation. 



Pure lactic acid is a colourless liquid, soluble in every pro- 

 portion in water and alcohol, of a purely acid taste, and so 

 strong and biting as to be almost insupportable. Its formula^ is 

 C, H,0„ or C, H, 0^ + HO. 



' Lehrbuch der Chemie, 1837, p. 512. * See Appendix I, Note 25. 



