In this preservative process is displayed a singular and important fact with regard to the agency of oxygen in putrefaction. The tin canisters being closed during the exposure to heat, must necessarily contain with the included matter some portion of air; and if heat were not applied, or even if applied imperfectly, putrefaction would take place. This proves that the effect of the high temperature is to produce some kind of combination of the oxygen of the air with the animal or included matter, not leading to putrefaction, or even counter-acting it, while by this combination it is effectually removed. The air accordingly, where the process is successful, is deprived of oxygen; but if the heat were not sufficiently prolonged, and by far the greatest part of the air in the vessel not exhausted, putrefaction soon comes on. From experiments that have been made on this mode of preserving alimentary substances, it has been proved, that if the vessels were opened only for a short time and again closed, without heat being applied, the inclosed substances soon putrefied: as they did also from mere exposure to the air. But if, after having been exposed even for an hour or two, they were re-placed, the vessels again treated as before, and then the due degree of heat applied, they could be preserved as at first. And this repeated exposure to the air, and removal of its operation by heating, it appears from Gay Lussac’s experiments, can be renewed a number of times. Nay, by occasional exposure to the heat of boiling water, without the exclusion of the air, he found the exemption from putrefaction to be attained. The theory of these effects is not very apparent. Gay Lussac supposes, that the oxygen may combine with that principle analogous to gluten, which excites fermentation, and which may equally excite putrefaction; that this by a kind of coagulation is separated by heat, and thus rendered inert; and that it is only that part of it which has suffered oxygenation which is capable of this coagulation; it is thus removed, while the exclusion of oxygen prevents the putrefaction from taking place, which would otherwise be excited by the remainder. But this is rather hypothetical and unsatisfactory. PRESERVATION OF MEAT BY POTTING. The process of potting consists in reducing cooked animal substances to a pulp, by beating the meat in a mortar, and incorporating the mass with a portion of salt and spices. The pulp is then put into a jar, and covered with a thick coat of melted butter or lard, to prevent the contact of air; and the surface is further protected with a bladder-skin tied over the mouth of the jar. The muscular part of meat is best suited for potting, and the quantity of salt and spices ought to be rather liberal. POTTED BEEF, GAME, OR POULTRY.