3. Various kinds of salt are used in the preservation of food. Saltpetre and sal prunella (which is saltpetre deprived of its water of crystallization by heat) are also used for the purpose. The action of these alkaline salts upon animal substances is, as already noticed, to abstract the water in the juices of the meat, and, being dissolved therein, the salts enter the pores of the animal substance; the albumen of the meat, which is more liable to putrefaction than the gelatine and fibrine, is thus rendered less so. There are two methods of salting, _dry salting_ and _pickling_. In dry salting, the meat is packed in dry salt, or in some cases the surface is rubbed all over with salt. In pickling, the meat is kept immersed in a solution (sometimes saturated) of common salt dissolved in water. This method does not render the meat so salt as dry rubbing, and is probably less injurious to its nutritious qualities, but it will not keep the meat so well. Bacon is _cured_ by salting and drying, for which latter purpose it is often hung up in the wide chimneys of farm-house kitchens; cod is also salted and dried for the large demand of the Peninsula; in England, it is used in a _green_ state; that is, instead of being split quite open, it is only opened down to the navel, then salted, and laid in brine or strong pickle, and put into casks without drying. Haddock, cod, or ling, are cured by splitting the fish and removing the backbone; they are then salted for two or three days, with equal parts of salt and sugar, or with salt alone; they are next stretched on sticks, and laid on the beach to dry in the sun, or they are arranged on stages, or hung up in an inclosed space warmed by a stove. Herrings are salted, or pickled, and smoked. Sugar, like salt, takes away the water from animal substances, and thus prevents putrefaction. By immersing meat in molasses, it has been preserved fresh for months. Fish is sometimes preserved by cutting it open, rubbing in sugar, and leaving it for a few days; it is then dried in the air, taking care to turn it frequently. For a salmon of six pounds weight, a table-spoonful of brown sugar is sufficient; but, if hardness be required, a teaspoonful of saltpetre is to be added.