592 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



The isolation of zinc lactate is necessary since the solution may also 

 contain other hydroxy acids, but in those cases in which no other hydroxy 

 acids are known to be present the estimation can be carried out with the ether 

 extract after removal of the ether. 



Note. The precipitation of proteins from muscle juice is effected by adding I volume 

 of hydrochloric acid and i volume of mercuric chloride. 



The extraction and estimation of lactic acid in urine is effected in a 

 similar way. 



(1) The urine (500 c.c.) is evaporated in vacuo at 50 to about 100 c.c. 

 and extracted with ether l in the extractor after adding 50 per cent, phosphoric 

 acid with or without the addition of ammonium sulphate. Ammonia is added 

 to the ether extract which is evaporated on the water-bath (50 c.c. -20 

 c.c.) ; this removes the ether and excess of ammonia. The solution is 

 distilled in the apparatus described above with 300 c.c. dilute sulphuric acid 

 (the reaction must be strongly acid) until 200 c.c. have passed over. A 

 second distillation using -oiN permanganate is then carried out : the titration 

 of this distillate as above gives the quantity of lactic acid (Dapper's pro- 

 cedure). 



(2) The urine (250 c.c.) is treated with phosphotungstic acid, excess 

 of which is removed with baryta and excess of baryta with carbon dioxide. The 

 solution is evaporated, acidified with phosphoric acid and the operations 

 described above carried out (Ishihara's procedure). 



(3) A similar procedure by Ryffel 2 depends upon the decomposition of lactic 

 acid into acetaldehyde with 50 per cent, sulphuric acid and the estimation of 

 the acetaldehyde colorimetrically. 



The method gives results which are about 80 per cent, of the theoretical, 

 if the estimation be effected by titration with bisulphite and iodine. The 

 direct distillation and estimation with bisulphite and iodine is the most conveni- 

 ent and rapid for routine work. 



45 c.c. of concentrated sulphuric acid are added to 40 c.c. urine in a 500 

 c.c. round bottom flask, the mixture being kept cold during the addition. The 

 flask is connected to a steam generator on the one side and a condenser on 

 the other. A rapid current of steam is passed in ; the temperature of the flask 

 as indicated by a thermometer as soon as distillation commences is about 140, 

 but should be raised by heating to 155 and kept within 2 of this temperature 

 by moderating the current of steam. The decomposition is complete in 30 

 minutes after about 100 c.c. have been collected. This distillate may be 

 titrated as above or again distilled after making just alkaline and estimated 

 colorimetrically. 



1 The ether is purified by shaking with 50 per cent, caustic potash and then with water 

 until the washings are free from alkali. 

 3 J. Physiol., 1909, 39, Proc. v. 



