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hour or more, and the flame being then extinguished bycovering the vessel close, the boiling is afterwards con-tinued, with a gentle heat, till the oil appears of a properconsistence : in which state it is called varnish. It isnecessary to have two kinds of this varnish, a more andless boiled, or a thicker and a thinner, which are occa-sionally mixed together as different purposes may require :that which is of a just consistence in warm weather provestoo thick in cold; and that which answers well for largecharacters, proves in the fame season rather too thin forsmall ones.

The thickest varnish is of such consistence when cold,that it draws into threads between the fingers nearly likeWeak glue : this is the mark by which the workmen judgeof the due boiling, a little of it being from time to timetaken out for this trial, and cooled by dropping it on atile or other cold body. It is very viscous and tenacious,like the soft resinous juices or thick turpentines. It isnot at all dissolved, any more than the oil at first, bywater or spirit of wine, but mingles readily enough withfresh oil, and unites with mucilages into a mass whichdissolves in water into a milky liquor : by boiling withstrong alcaline ley it forms a soapy compound; whencethe types, after an impression, are cleaned from the ink,by washing, and rubbing them with a brush, in hot ley.The oil emits, during the whole time of the boiling, veryoffensive penetrating fumes : when grown cold, it has anacrid disagreeable taste, but little ill smell. The oil is saidto lose, in being boiled into thick varnish, from a tenthto an eighth part of its weight, which proportions agreesufficiently with my trials: common linseed oil, boileddown to a consistence which appeared somewhat too thick,lost about one sixth : being further boiled, till it becamequite firm when cold, the loss was near one half. Diffe-rent

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