204 Mr, W. K. Sullivan on the nature of Lactic Fermentation. 



observed to form upon the sides of the bottle, consisted of the 

 solid acids of the series C" H° 0'' in a crystaUized state. This 

 fact is interesting in connexion with the chemical changes w^hich 

 the substance knowTi as boff butter must have undergone in time, 

 as I shall show in a future paper. 



A portion of the filtered acid solution was distilled in a retort ; 

 a faintly acid liquor came ovei", smelling strongly of butter. When 

 neutralized with baryta, and the solution evaporated and set 

 aside over sulphuric acid, crystals were obtained which had the 

 characters of baryta salts formed with the volatile acids of butter. 



When a portion of the filtered acid liquor was treated with 

 moist freshly prepared oxide of zinc, so as to neutralize a consi- 

 derable portion of the free lactic acid, and then heated, it coagu- 

 lated exactly like a solution of albumen. A portion of the acid 

 liquor, without the addition of oxide of zinc, on being evaporated, 

 did not appear to produce in a very distinct manner the pellicle 

 so characteristic of a solution of caseine. Bichromate of potash, 

 iodate of potash, and ferrocyanide of potassium gave the usual 

 precipitates in the acid solution, which may be obtained either 

 with albumen or caseine. 



A portion of the acid solution, on being mixed with a solution 

 of chloride of ammonium, coagulated on being heated. A similar 

 result was obtained with common salt, chloride of potassium, 

 sulphate of soda, sulphate of potash, and nitrate of potash. The 

 larger the quantity and the stronger the solution of the alkaline 

 salt, the lower was the temperature at which the coagulation 

 took place. The precipitates formed at very low temperatures 

 were soluble in pure water ; but the solutions were not coagu- 

 lated by heat, though precipitable by ferrocyanide of potassium. 

 When recently thrown down and rapidly filtered, they dissolved 

 in acetic acid. Sti'ong alcohol also gave a precipitate in the ori- 

 ginal solution. 



The distinctive tests for albumen are coagulation by heat, and 

 when a free acid is present, coagulation on the addition of a salt 

 with an alkaline base, the temperature of coagulation being 

 less as the proportion of salt increases. So far, therefore, as 

 these tests can be relied upon, it would appear that the caseine 

 of the milk was converted into albumen in the presence of the 

 lactic acid formed from milk sugar, in the absence of air. If 

 this was a simple metamorphosis, it would support the view that 

 caseine was merely an albuminate of soda, — so strongly held, 

 among others, by M. Gerhardt. It is, however, very probable 

 that the change is not so simple as this would make it : for how, 

 in this case, was the lactic acid formed ? A portion of the caseine 

 must have first been modified into a lactic ferment, and the re- 

 mainder converted into albumen, according as the lactic acid was 



