4. The efficacy of _smoking_, or _smoke-drying_, arises not only from the heat of the smoke, but from certain chemical products disengaged during the combustion of the wood fuel used for the purpose. Pyroligneous acid vapor and creasote are both produced, and the latter substance possesses the remarkable property of coagulating albumen. Hence, those chimneys only are fit for the purpose where the fire below is wood or peat, not coal. The kind of wood burnt is also of importance, the smoke from beech and oak being preferable to that from fir or larch. Smoke from the twigs of juniper, rosemary, peppermint, &c., impart to the meat a portion of their aromatic flavor. Westphalia hams owe some of their excellence to being smoked by juniper. Slow smoking is preferable to rapid, as it penetrates completely into the interior of the meat. In some parts of the country, the drying and smoking of hams are a separate trade. In such cases, a smoking-house or hut is erected, about twelve feet square, and the walls seven feet high, with a hole in the roof; joists are laid across inside, to hang the flitches on, and the floor is covered five or six inches deep with sawdust, which, being kindled, produces much smoke and little flame. 5. Vinegar and some other acids preserve both animal and vegetable substances by coagulating their albumen, which, as already stated, is peculiarly liable to putrefactive fermentation. 6. In the year 1810, M. Appert received a reward of 12,000 francs from the French Government for his method of parboiling provisions, and inclosing them in earthenware vessels in such a manner as to exclude the air. Many vegetables, fruits, &c., can be kept fresh for a great length of time, by shutting them up closely in a vessel, having previously filled up the interstices with sand or other loose substance that will exclude nearly all the air. Fresh walnuts may be preserved in this way in a jar, packed with sand and closely covered over; grapes packed in sawdust are imported into this country. Meat cannot be preserved in this way, but by exposing it to the heat of boiling water, the albumen, in which putrefaction first commences, coagulates; and as coagulated albumen is somewhat slow in decomposing, we thus have a reason for the common observation that cooked meat will keep longer than raw. It will not, however, keep many days, unless the air be perfectly excluded, not only from the external, but from the internal parts. The air in the interior may be expelled by boiling, and the exterior air may be kept away by inclosing the substance in an air-tight vessel. If these conditions be carefully observed, food may be preserved for any length of time. Appert's method consists in applying heat to the substances to be preserved, so as to coagulate their fermentable juices, and then to place them in such a situation as to deprive them of contact with air. The vessel in which the meat is prepared