CH. VII.] LACTIC ACID. 181 



saturated solution of copper sulphate. Mix and place the tube in a 

 beaker of boiling water for about five minutes. Cool thoroughly 

 under the tap, add two drops of a 0-2 per cent, alcoholic solution of 

 thiophene, and shake. Replace the tube in the boiling water bath. 

 As the mixture gets warm a fine cherry-red colour develops. 



NOTE. Lactic acid is oxidised in sulphuric acid solution to formaldehyde 

 and acetaldehyde which react with thiophene in the presence of an excess of 

 sulphuric acid to give a cherry-red colour. The copper sulphate aids this 

 oxidation, which is inhibited by water. 



230. Uffelmann's reaction for lactic acid. Treat a few cc. 

 of Uffelmann's reagent with a few cc. of a dilute (0-4 per cent.) 

 solution of lactic acid. The violet colour is instantly turned to 

 a yellow. 



NOTES. i. Uffelmann's reagent is prepared by treating a i per cent, 

 solution of phenol (carbolic acid) with very dilute ferric chloride till the 

 solution becomes coloured an amethyst-violet. 



2. The reaction is not very reliable, since other acids as tartaric, oxalic 

 and citric give it. 



231. The Formation of Lactic Acid in Fatigue. A pithed 

 frog is kept on ice for about half-an-hour. Remove one hind limb 

 and replace it on the ice. Expose the lumbar plexus of the other 

 side and stimulate it electrically by means of a strong interrupted 

 current for at least ten minutes. Cut off the hind limb, strip the 

 skin off the two limbs and treat the muscles separately as follows : 

 Rapidly remove the muscles, grind them with ice-cold 95 per cent, 

 alcohol and sand. Transfer the mixture to a beaker, and warm for 

 a few minutes on the water bath. Filter through a small paper 

 and evaporate to complete dryness on a water bath. Treat the 

 residue with about 5 cc. of cold water and rub it up thoroughly 

 with a glass rod. Filter and boil the filtrate with as much animal 

 charcoal as will lie on a threepenny piece. Filter and evaporate 

 the filtrate to complete dryness on a water bath. Allow the residue 

 to cool and apply Hopkins' test by treating the residue with strong 

 sulphuric acid, shaking round till solution is obtained, transferring 

 to a dry test-tube, adding three drops of saturated copper sulphate, 

 etc. A fine red colour develops in the tube containing the extract 

 from the tetanised muscle, but none or very little in the other. 



CALIFORNIA COlUi 



of CY ' 



