A substance obtained from the oil found in the head of several species of whale, but chiefly from the physeter macrocephalus. Though analogous to fat and wax, it differs from them in several properties. It is of a flaky texture - soft, white, and brilliant; melts at 113°; and by raising the heat may he volatilized with little change, though by repeated distillation it is decomposed. It burns with a clear flame. A property distinguishing it from fat is that of solubility in alcohol and ether, though it is but sparingly soluble in the former. It dissolves more rapidly and abundantly in warm ether, from which it precipitates when cool: oil of turpentine acts upon it in a similar manner. Spermaceti is found in a large triangular trunk, four or five feet deep, and ten or twelve long, filling almost the whole cavity of the head, and seeming to be entirely different from the proper brain of the animal. The oil is separated from it by dripping. In this state it has a yellow, unctuous appearance, and is brought to England in barrels. An ordinary sized whale, it is said, will yield upwards of twelve large barrels of crude spermaceti.

The mode of purifying it in the large way is as follows: - the mass is put into hair or woollen bags!, and pressed between plates of iron, in a screw-press, until it becomes hard and brittle. It is then broken into pieces, and thrown into boiling water, where it melts; and the impurities which rise to the surface, or sink to the bottom, are skimmed off or separated from it. After being cooled, and separated from the water, it is put into fresh water in a large boiler, and a weak ley of the potash of commerce added to it by degrees. This part of the process is thrice repeated, after which the whole is poured into coolers, when the spermaceti concretes into a white semi-transparent mass, which, on being cut into small pieces, assumes the flaky appearance which it has in the shops. Some adulterate it with wax; but the deceit is discovered, either by the smell of the wax, or by the dulness of the colour. Some also sell a preparation of oil taken from the tail of the whale, instead of that from the brain; but this kind turns yellow as soon as exposed to the air. Indeed, it is apt, in general, to grow yellowish, and to contract a rancid, fishy smell, if not carefully secured from the air.

The more perfectly it has been purified at first, the less susceptible it is of these alterations; and after it has been changed, it may be rendered white and sweet again by steeping it afresh in a ley of alkaline salt and quicklime. It melts in a small degree of heat, and congeals again as it cools.

The great use of spermaceti is for making candles, and it is also employed in medicine. Spermaceti candles are of modern manufacture: they are made smooth, with a fine gloss, free from rings and scars, superior to the finest wax candles in colour and lustre; and, when genuine, leave no spot or stain on the finest silk, cloth, or linen.