LACTIC ACID. 91 



are sufficiently acquainted with the properties of lactic acid and its 

 salts, we may modify this method in many respects, which is indeed 

 the more necessary, since, in investigations relating to animal che- 

 mistry, we rarely ha^ e so large a quantity of material to work upon 

 as is required in accurately following the steps laid down by Liebig. 

 From most of the other animal fluids we can rarely obtain a suffi- 

 cient quantity of lactic acid to serve for an elementary analysis. 

 Indeed it often happens that we cannot even obtain enough of a 

 pure lactate to enable us to determine the atomic weight. Hence, 

 it is very often necessary to found our decision regarding the pre- 

 sence of lactic acid almost entirely on the crystalline form of its 

 salts. Although many of the other properties of the lactates may 

 contribute to establish the proof of the presence of this acid, yet a 

 crystallometric investigation, made with the aid of the microscope, 

 can alone be regarded as approximating in certainty to an elemen- 

 tary analysis. 



In consequence of the extremely minute quantity of lactic acid 

 to be obtained from the animal fluids, I am in the habit of adopt- 

 ing the following method, which may be readily modified in parti- 

 cular cases, with the view of studying the forms of the different 

 salts under the microscope. The impure lactic acid prepared from 

 the alcoholic extract by sulphuric or oxulic acid is treated with 

 baryta-water, and the excess of the baryta removed by carbonic 

 acid ; the solution of lactate of baryta is evaporated to the con- 

 sistence of a syrup, treated with alcohol, filtered, again evaporated, 

 and then allowed to stand for some time, in order that the other 

 baryta-salts, (for instance, the butyrate and inosinate) may crystal- 

 lise ; the syrup is then allowed to trickle away, or if it be not with- 

 drawn, is dissolved in water and decomposed with a solution of 

 gypsum ; the fluid from which the sulphate of baryta has been 

 removed by filtration is strongly concentrated, and on examining it 

 under the microscope we can readily perceive the double brushes of 

 lactate of lime which we have already described, in addition to 

 crystals of gypsum. On dissolving these crystals of lactate of lime 

 in alcohol, and adding sulphate of copper to the alcoholic solution, 

 the fluid, after standing for some time (in order that the excess of 

 of sulphate of copper and the gypsum that is formed may separate 

 as completely as possible) is evaporated so as to crystallise, and the 

 crystals of lactate of copper are then microscopically examined. If, 

 by the above process, we do not succeed in obtaining distinct and 

 measurable crystals, we must dissolve the residue in a little water ; and 

 (in order to decompose or separate any butyric acid that may be 



