~63. The Animal Oils~ have had a wide and varied application in general machinery, and much testimony might be produced to show the superiority of any one kind over all the other kinds. Each variety has some particular property which some of the others may not have to such a degree. ~64. Porpoise Jaw Oil[13] and Blackfish Melon Oil~ have certain good qualities which have made them very popular, particularly on this side of the Atlantic. When properly refined (4-6) they are no doubt very suitable for the work of reducing friction in small and delicate mechanism. ~65. Sperm Oil~ (7) had been used to some extent as a lubricant for time-keeping contrivances; in fact, many tower clock experts still employ it on the heavier bearings. A. Long, writing to the British Horological Journal, describes a trip to the Arctic regions in 1814 and 1815, in which he states that a certain portion of the sperm oil they obtained never congealed, which they preserved and applied to their chronometers, and thus kept them going through the winter. Others have experimented with it, and it was at one time largely used; while some tower clock makers claim that they find it satisfactory. It is, however, open to the objection that it would produce serious variation when used in time-keeping mechanisms, as its _viscosity varies greatly with varying temperatures_ caused by the alteration of the spermaceti it contains, thus causing sudden fluctuations of its coefficient of friction (81). It also absorbs oxygen rapidly when it is exposed to the air and loses quality seriously, gradually becoming "gummed" or resinous. A gain of two to three per cent in weight in twelve hours when exposed to the air at 140° F. (60 C), is caused by this absorption of oxygen (10). ~66. Bone Oil~ (8) has been widely used both in this country and in Europe, and possesses some good qualities, not the least of which is the property of resisting evaporation and oxidation. ~67. Neatsfoot Oil~ (9) has been largely used, especially in Europe. The writer regrets that he has not procured samples in order to ascertain its relative value. ~68. Olive Oil~ (10) has at least one good quality. It is one of the most perfectly non-drying of all the oils, resisting both oxidation and evaporation (24). But it is next to impossible to entirely remove its acid qualities, small traces of which remain after the most thorough treatment. It is also liable to decomposition, generating acids even after refinement.