CASEIN. 191 



potash and soda, when diluted with water and cold. Caustic 

 ammonia dissolves it very slowly and imperfectly. 



When cheese coagulated by rennet is burnt, it leaves 6 per 

 cent, of subsesqui -phosphate of lime, and half a per cent, of caus- 

 tic lime, which had been in combination with the casein in the 

 milk. 



When cheese is long kept, it undergoes peculiar alterations, 

 which have been investigated by Braconnot* He mixed 270 

 grammes of skim-milk cheese with a litre of water, and left the 

 mixture a month to putrefy, at a temperature between 68 and 77. 

 The greatest part of the cheese dissolved, and the solution was 

 separated from the undissolved portion by filtration. It had a 

 putrid smell, without anything sulphureous. Being evaporated 

 to the consistence of honey, it gradually congealed into a gra- 

 nular mass. Alcohol dissolved a portion of this matter, and left 

 a portion untouched. 



The undissolved portion was dissolved in water and treated 

 with animal charcoal, which deprived it of its colour. Being now 

 left to spontaneous evaporation, it gave small brilliant crystalline 

 vegetations, and fine needle-form crystals, constituting cauliflower 

 rings round the borders of the liquid. To obtain this substance 

 white, it was necessary to dissolve and crystallize it several times. 

 Braconnot distinguished this substance by the name of apose- 

 pedin. f Proust had previously called it caseic oxide. Its 

 properties have been already detailed in a former part of this 

 volume. The first attempt to analyze casein was made by The- 

 nard and Gay-Lussac. The casein which they employed was 

 obtained by spontaneous coagulation. It was washed thoroughly 

 with water, and then dried and pulverized. It was then burnt 

 with chlorate of potash, and the quantity of carbonic acid, &c. ob- 

 tained, determined from which the constituents were inferred.^ 

 Mulder has shown that its base is protein, and that it consists of 

 ten atoms of protein united to one atom of sulphur, or 10 

 (C^'H 31 Az 5 O 12 ) + S. Dr Scherer also subjected it to analy- 

 sis. Milk was mixed with twice its bulk of alcohol ; and the 

 coagulum was boiled repeatedly in alcohol and ether. When all 

 the butter was removed, the coagulum was boiled in water to se- 



* Ann. de Chim. et de Phys. xxxvi. 159. 



f From euro and rmrtJetv, putrefaction. 



| Recherches Physico-Chimiques, ii. 382. Ann. der Pharrn. xl. 40. 



