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The Digester

217. Usually named after its inventor, Pepin (see fig. 129), is a strong iron vessel with a moveable handle, by which it may be suspended over the fire. In the centre of the lid is a metal valve, which should always be attended to, as it might otherwise rust in its socket, and occasion the bursting of the pot. A little grease prevents this, but the greatest preventive is cleanliness. Besides this valve, which allows the steam to escape as soon as it rises with sufficient force to overcome the weight of the piece of metal, there is a peculiar adaptation of the lid, by which it is very securely closed. It is not only placed upon the top of the digester, but, by a twist, it is hooked under three projecting arms (see fig. 129), and is consequently kept down closely, its under surface being ground to correspond with the upper edge of the pot. When, therefore, the bones, &c., are placed in the digester with water, and the lid adapted to it properly, the heat is raised considerably above 212 degrees, because the pressure is greater than that of the atmosphere by the weight of the valve. The consequence is, that bones are compelled to give out their gelatine, and are left almost with nothing but their lime. This is the most economical or all cooking utensils, and is the means of saving an immense amount of nutritive matter; but it is of no use whatever unless the lid is securely adapted to the pot.