Sect. i.

Epitome of Chemistry.

ixfii

of vegetables. It is highly nutritious. Officinal.- White of

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284. Fibrin is of a white colour, without taste or smell,tough and elastic; but when dried, hard and almost brittle.It is not soluble in water or in alcohol. The concentratedcaustic alkalies form with it a kind of fluid viscid soap. It isdissolved even by the weak and diluted acids ; but it undergoessome change, by which it acquires the properties of jellying,and being soluble in hot water. By maceration in water, itbecomes putrid, and is converted into adipocire. By longboiling in water, it is rendered tough and corneous. Whendecomposed by heat or nitric acid, it is found to contain alarge proportion of nitrogen. It forms the basis of the mus- 1cular fibre, and is contained in small quantity in the blood.'The gluten of wheat does not seem to differ from it in anyimportant property. It is eminently nutritious.

285. Urea is obtained in the form of brilliant micaceouscrystals, in groups, forming a mass of a ; yellowish-white co-lour, adhering to the vessel containing it $ difficult to cut orbreak : hard and granulated in its centre, gradually becomingsoft, and of the consistency of honey on its surface; of a strong,disgusting, alliaceous odour; of an acrid, pungent, disagree-able taste. It is deliquescent; and during its solution in wa-ter, it causes a sensible diminution of temperature ; it is alsosoluble in alcohol, especially when assisted by heat. On cool-ing, the alcoholic solution deposites crystals of pure urea. Bythe application of heat, it melts, swells rapidly, and at thesame time begins to be decomposed, emitting an insupportablyfetid odour, and is converted into carbonate of ammonia, andcarburetted hydrogen gas. Urea is charred by concentratedsulphuric acid ; diluted sulphuric acid, aided by heat, is capa-bleof converting it entirely into acetic acid and ammonia;concentrated nitrous acid decomposes it with rapidity ; dilutednitric acid, aided by heat, changes it almost entirely into car-bonic acid gas and nitrogen gas ; muriatic acid dissolves andpreserves it; oxymuriatic acid converts it into ammonia andcarbonic acid ; potass, aided by heat, converts it into the car-bonate and acetate of ammonia. It influences the form of thecrystallization of the muriates of ammonia and soda. Thesolution of urea in water varies in colour from a deep brownto a pale yellow, according to its quantity. With eight partsof water it is perfectly fluid; it scarcely undergoes spontane-ous decomposition when pure, but the addition of some albu-men occasions it to putrify rapidly. By repeated distillationit is entirely converted into carbonate of ammonia. With ni-