Lard, the oily portion of hogs' fat, separated from the animal tissues by the process called rendering, which is melting it out at the temperature of boiling water, and commonly with the mixture of a small quantity of water. The best and firmest lard is obtained exclusively from the fat which surrounds the kidneys; but the common qualities of commerce are derived from the entire fat of the animal. To render this harder various adulterating substances are added, as mutton suet, starch, potato flour, and even caustic lime. Alum also is often added with the view of increasing its whiteness; and in England common salt and the carbonates of soda and potash have been detected in samples of it. The presence of water and its quantity may be determined by submitting a weighed portion to moderate heat; it escapes in bubbles, and when these cease to appear the loss of weight indicates the proportion. If starch is present, it will cause a solution of iodine with which a particle of the lard is mixed to turn blue or even black. The proportion of the adulterating ingredients sometimes amounts to more than 25 per cent., of which the chief article is some farinaceous substance. Water has been found to the extent of 12 per cent.; alum of 2 to 3 per cent.; and quicklime of 1 per cent.

Lard as prepared is run into kegs, but the best qualities are collected in England in bladders, and are distinguished by the name of bladder lard. When pure, the article should be firm and white, and entirely free from taste or smell; it should melt at 212° F. without bubbling, and without depositing any sediment; the melted fluid should be nearly as clear and transparent as water. Its melting point varies from 78.5° to 87.5° F. Its composition in 100 parts, as given by Braconnet, is: stearine and margarine 38, oleine 62. - Lard is extensively used in culinary operations as an article of food; it enters into the composition of pastry, and is the material in which fish and other articles are commonly fried. In this operation the presence of flour is sometimes indicated by the substances fried adhering to the pan. In pharmacy lard is the material which forms the bulk of most of the ointments and cerates, and may be used alone as an ointment. A good article for this use, that contains no noxious ingredients, and is not liable to melt in warm climates, is difficult to be procured. The tendency to rancidity may be partly counteracted by adding to the melted lard a tincture of benzoin, of guaiacum, or of poplar buds.

The oil of pimento and balsam of Peru are said to have the same preservative influence. The substance is also employed for lubricating machinery, for which use it is particularly important that it should be free from glutinous adulterants. - By the separation of the stearine and margarine from lard the oily product called lard oil is obtained. The manufacture of this is carried on to an immense extent in Cincinnati and Chicago. Of the stearine are made candles, and other portions of lard enter into the production of soap. A large portion of this oil is sent to France, where by the skill of the chemist it is incorporated with olive oil to the amount of GO or 70 per cent., the mixture then coming back to be sold as pure olive oil. Some interesting properties of lard when combined with rosin, in the proportion of 3 parts by weight of lard to 1 of rosin, were communicated by Prof. Olmsted to the American association at their meeting in New Haven in 1850. When melted together, the mixture is semi-fluid in cold weather. When applied to leather, it renders it very soft and impermeable to air and moisture, and it is particularly well adapted for lubricating the pistons of air pumps, as it is found to protect the brass from corrosion, which the ordinary lubricants induce.

The rosin appears to prevent the formation of an acid in the lard, and thus the compound is well adapted to protect the surface of any metal from rust. When used for iron, a little powdered graphite may be added. When the mixture is used instead of other oily substances for making soap, the tendency of this to become rancid when wet and remaining damp is checked. Other uses readily suggest themselves. As an illuminating agent in solar lamps, Prof. Olmsted found lard oil combined with rosin superior for a time to lard oil alone,, but the wick after a time became clogged, lessening the brilliancy of the light. - In the year 1873-'4, 191,139,000 lbs. of lard were produced in the United States, chiefly in Illinois and Ohio; the product in the preceding year was 218,655,238 lbs. The chief centres of this industry are Chicago and Cincinnati. In 1873, 230,534,207 lbs. of lard, valued at $21,245,815, were exported from the United States, chiefly to Germany, England, and Belgium. The amount of lard oil exported was 388,836 gallons, valued at $298,731. According to the census of 1870, the total value of the lard oil produced in the United States in that year was $2,552,510.