This section is from the book "Three Meals A Day", by Maud C. Cooke. Also available from Amazon: Three Meals a Day.
Cut the fat in small pieces, either the leaf or the side pork. Put in 1 pint of water to a No. 8 kettle full of lard. Simmer slowly, stirring frequently and watching that it does not burn. When the scraps are just beginning to get brittle and brown add a tablespoonful of fine salt to a quart of the lard, and the lard will keep perfectly sweet for any length of time. By knowing the size of the kettle used it will be easy to estimate the quantity of salt required. The salt does no possible harm to any kind of cookery, and makes the lard whiter and harder. Let it. cook slowly for a short time after adding the salt. Strain through a coarse cloth, always squeezing the last drops into a separate jar for common uses. Dip the cloth in boiling water now and then to free from grease. Earthenware should be used for holding the lard and several small vessels are preferable to a single large one, as preventing the necessity of disturbing the entire quantity each time. The jars may be covered with bladders or cloths dipped in grease.
Put the tainted lard in a kettle and cut salt pork in thin slices, ½ pound of pork to a gallon of melted lard. Add 2 spoonfuls of salt and cook until the pork is crisp. Remove the slices of pork, turn the lard into a jar, and it will be found perfectly sweet. The use of salt, however, will prevent all such trouble. Some housewives substitute sliced Irish potatoes, raw; the pork will be found preferable.
 
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