Salt and sugar have been used as preservatives, one might almost say, since time immemorial. Smoke, and a small amount of heat, as in making bacon, might be listed among preservatives.
The word "preservative," as now used, means powders used for keeping fruits, meats, milk and other food in a fresh condition. These preservative powders ars sold under many different names, but each usually contains some chemical which is injurious to health. Borax, boric acid, salicylic acid, and formalin are the chemicals generally used. A preservative may contain one or more than one of these.
References: Common Sense in the Household - Harland - pp. 463-467; Parloa's Kitchen Companion, pp. 84-90, 827, 834-846; The Art of Cookery - Ewing - pp. 163-165; Food Products of the World - Green - pp. 35-37; Boston Cook Book - Lincoln - pp. 401-403; Elements of Cookery - Williams & Fisher - pp. 282-286; Ann. Rep. Minn. Exp. Station 1899, pp. 516, 517.
There is no reason why foods should not be preserved in the household by those good old methods practiced by our forefathers. Drying and canning fruits and vegetables, salting and smoking meats, and either sterilizing milk, or subjecting it to sufficient cold to prevent its souring in a reasonable length of time. Such methods of preserving are effective, and the products are wholesome, but the preservatives sold and used are very generally harmful.