Familiar letters on chemistry. Second series, The philosophical principles and general laws of the science / By Justus Liebig ... Edited by John Gardner.

  • Liebig, Justus, Freiherr von, 1803-1873.
Date:
1844
Catalogue details

Licence: Public Domain Mark

Credit: Familiar letters on chemistry. Second series, The philosophical principles and general laws of the science / By Justus Liebig ... Edited by John Gardner. Source: Wellcome Collection.

    180/244 (page 164)
    order to make milk coagulate, or, in other words, to effect a separation of the cheese from the other constituents of milk. The solubility of cheese in milk is in conse- quence of the presence of alkaline phosphates and of free alkalies. In fresh milk these substances may be easily detected by the property it possesses of restoring the blue colour to reddened litmus- paper. The addition of any acid, by neutralising the alkali, causes the cheese to separate in its naturally insoluble state. The acid indispensable for the coagulation of milk is not added to the milk in the preparation of cheese, but it is formed in the milk at the expense of the milk-sugar pre- sent. A small quantity of water is left in contact with a small piece of a calf’s stomach for a few hours or for a night;—the water absorbs a quan- tity of the decomposed mucous membrane so minute as to be scarcely ponderable; this is mixed with milk; its state of transformation is communi- cated (and this is a most important circumstance) not to the cheese, but to the milk-sugar, the elements of which transpose themselves into lactic acid, which neutralises the alkali, and thus causes the separation of the cheese. By means of litmus- paper the process may be followed and observed