The process of canning involves the making and soldering of two punctured holes in the top of each can. The presence of three such holes is evidence that the can had been im perfectly treated, and that it was reheated, the gas allowed to escape and the hole punctured for this purpose again sealed. The contents of such reheated cans are more likely to be of inferior quality than those of properly pre pared cans. On this account the packers are careful to make the third puncture as incon spicuous as possible, and, often to conceal it entirely by making it on the side of the can near the top and pasting the label over it. This may usually be detected by running the finger around the rim of the can.
Sometimes newly-packed cans are so much swollen that reheating is not sufficient. In such cases the cans are opened, the contents sorted and the sound parts repacked in cans as before. The quality of such articles can only be deter mined by opening the cans and examining their contents, which present an overcooked appear ance. First-class canned goods have the name of the manufacturer and often that of the wholesale house through which they are sold upon the labels, while doubtful goods have a fictitious factory name and no dealer's name.
Canned peas are subject to great variations in quality. Dried peas are bought in large quantities, soaked, cooked and canned. Such articles can usually be recognized by their ap pearance and taste on opening the cans. To such an extent is this done as to have led to legislation in some States requiring all such cans to be legibly marked French canned peas and beans are often colored with sulphate of copper, which im proves their appearance, but not their taste. The sale of such articles is forbidden in some countries.
The Composition of Canned Meats.-- Konig found the following results in samples of canned meats and salmon. From 48 to 65 per cent of water, from 15 to 33.8 per cent of nitrogenous substances, from 0.2 to 21.6 per cent 'of fat and from 2.3 to 21 per cent of ash. Of the water-free substances, there were from 43 to 78 per cent of nitrogenous substances and from 0.3 to 43 of fat. The albuminous sub stances were generally less than those of fresh meat, the actual figures varying in different kinds of meat, from 87.06 to 93.94 per cent • as much as that of fresh meat.
The preservation of food by hermetic seal ing in cans has, within the last half century, grown to be an important factor in the com mercial and industrial development of the United States. Before 1795 drying and the use of salt and sugar were the only methods used to any extent in the preservation of food.
Nicholas Appert, a Frenchman, stimulated by the offer of a reward for a mode of preserving food for use at sea in the navy, submitted to his government a treatise upon the hermetic sealing of all kinds of food. His principle, as set forth in this work, was practically the same as that which is now in use in canning, the exclusion of air and the application of heat for the purpose of sterilization. France first purchased his process and the industry soon spread to England and Ireland.
One of the first persons who introduced the industry into the United States was Ezra Dag gett, who arrived in New York between 1815 and 1818. In 1819 he was engaged in the manu facture of hermetically sealed goods, chiefly salmon, oysters and lobsters. William Under wood arrived at New Orleans from London in 1817, having learned the trade of pickling and preserving with the house of Mackey & Com pany. Not liking the climate of the South he went from New Orleans to Boston, where he and Charles Mitchell introduced the same in dustry, applying it to pickles, sauces, jams and fruit. Glass jars were at first used, but on ac count of their expense and fragile nature, they were soon largely supplanted by tin cans, which were introduced in 1825 by Thomas Kensett. The making of tin cans for this purpose be came an important industry, various improve ments being made from time to time in the processes of manufacture.
During the Civil War large quantities of canned meats, tomatoes and other vegetables and fruits were furnished both to the army and to the navy, and during the Spanish War the use of preserved meats treated with chemical antiseptics at one time threatened to become a government scandal.
According to the 1910 census there were in the United States in 1909 3,787 establishments for the canning and preserving of fruits and vegetables, fish and oysters, pickles, preserves, jellies and sauces. They employed an aggre gate capital of $119,207,127. This was divided thus: $67,313,424 in fruit and vegetable can ning; $18,796,180 in fish canning; $3,647,136 in oyster canning and $29,450,387 in making pick les, preserves and sauces. The total number of wage-earners employed was 59,968, and .the amount paid in wages $19,081,843. (These fig ures and the following do not include those for the canning of meats in packing-houses, nor the canning of condensed and evaporated milk, for which separate statistics are not collected).