Although, however, the preservation of alimentary matters by the total exclusion of air, assisted by sub jecting them to a certain degree of heat, has long been practised in some degree, we are certainly in debted to M. Appert, • who first published in 1810, for the regular and scientific application of these principles upon a large scale. From extensive expe. rience and long perseverance he became convinced, " 1st, That fire has the peculiar property, not on ly of changing the combination of the constituent parts of vegetable and animal productions, but also of retarding, for many years at least, if not of destroy ing, the natural tendency of those same productions to decomposition.
" 2d, That the application of fire in a manner variously adapted to various substances, after having, with the utmost care, and as completely as possible, deprived them of all contact with the air, effects a perfect preservation of those same productions, with all their natural qualities." Upon these principles he invented many processes adapted to the different natures of the substances to be preserved; but the fundamental conditions con sist, 1st, In inclosing in bottles the substances to be preserved. ed, In corking the bottles with most care ; for it is chiefly on the corking that the success of the process depends. 3d, In submitting these inclosed cases to the action of boiling water in a water-bath (Balneum Mariae), for a greater or less length of time, according to their nature, and in the manner pointed out with respect to each several kind of substance. 4th, In withdrawing the bottles from the water-bath at the period described.
M. Appert employed at first bottles made of glass, which it was difficult to close exactly, especially when their mouths were large ; but he now uses cylinders of tin plate, which are soldered up after they are filled. This is especially an improvement for ani mal substances, which require much more attention than vegetables. Tin cases, or canisters, seem to have been first used in London by Messrs Donkin and Gamble, by whom a very ingenious method of testing the provisions put up by them was also in vented as early as 1813. t The substances to be pre. served are first parboiled or somewhat more. The vegetables and meat, the bones being removed, are then put into tin cylinders, which are filled up with the broth and the lid soldered down. It now un dergoes the remainder of the cooking, when a small hole is opened at the top of the cylinder, and immediately closed with solder while still h6t. The whole is now allowed to cool, and from the dimi nution of volume in the contents, in consequence of the reduction of temperature, both ends of the cylinder are pressed inwards and become concave.
The cases thus hermetically sealed are exposed in a test-chamber for at least a month, to a tem perature above what they are ever likely to en counter ; from 90° to 110° Fahrenheit. if the pro cess has failed, putrefaction takes place, and gas is evolved, which in process of time will bulge out both ends of the case, so as to render them convex, in stead of concave. But the contents of whatever cases stand this test, will infallibly keep perfectly sweet and good in any climate, and for any length of time. Another advantage is, that if there be any taint about the meat when put up, it inevitably ferments, and is detected in the proving.
All kinds of alimentary matters may be pre. served in this way,—beef, mutton, veal, and poul try, boiled and roasted, soups, broths and vegeta bles, creams and custards. The testimonies in, favour of the success of the process are of' the most unexceptionable kind. The meat is put up in ca• nisters of from 4lbs. to 20 lbs. weight each ; and the milk and soups in quart or pint bottles. The meat is charged from 1 s. 8d. to 3s. a pound ; roast higher than boiled, and veal dearer than mutton or beef. The milk is 24s.per dozen for quarts, 15s. for pints, and 10s. for half pints ; and soups from 30s. to 60s. per dozen for quarts. The weight of the ca nister is deducted, and nothing is charged for ca niiters or bottles ; and it should be observed, that the patent provisions being cooked, and without bone, render them nearly equivalent to double the weight of meat in the raw state ; for, by experiment, the patentees found, that the waste in cooking and weight of bone are about one half. Captain Neish took a quantity to India, not one canister spoiled ; and one which he brought home contained beef in • the highest state of preservation after two years, and haring been carried upwards of 35,000 miles in the warmest climates. The commissioners for victualling the navy also examined some nearly four years old, which had been in the Mediterranean and Quebec, and found it as sound, sweet, and fresh, as if it had been only yesterday boiled. We are enabled to add the testimony of that distinguished navigator Captain Basil Hall, who has liberally communicated to us the result of his personal experience and observation : " I can answer for the perfect preservation of a great number of cases which were in my possession during the voyage to China. I had L. &S worth, and not one failure. At that time milk was preserved in hot. ties corked ; but tin cases have been substituted with very great effect, as I have myself tried. It is really astonishing how excellent the milk is ; and, indeed, every thing preserved in this way is good.