=Cyanuric acid= (C₃O₃N₃H₃), one of the decomposition products obtained from urea, is poisonous, the symptoms and pathological effects closely resembling those due to hydric cyanide. In experiments on animals, there has been no difficulty in detecting prussic acid in the lungs and liver after poisoning by cyanuric acid. XIII.--Phosphorus. § 272. =Phosphorus.=--Atomic weight 31, specific gravity 1·77 to 1·840. Phosphorus melts at from 44·4° to 44·5° to a pale yellow oily fluid. The boiling-point is about 290°. The phosphorus of commerce is usually preserved under water in the form of waxy, semi-transparent sticks; if exposed to the air white fumes are given off, luminous in the dark, with a peculiar onion-like odour. On heating phosphorus it readily inflames, burning with a very white flame. At 0° phosphorus is brittle; the same quality may be imparted to it by a mere trace of sulphur. Phosphorus may be obtained in dodecahedral crystals by slowly cooling large melted masses. It may also be obtained crystalline by evaporating a solution in bisulphide of carbon or hot naphtha in a current of carbon dioxide. It is usually stated to be absolutely insoluble in water, but Julius Hartmann[271] contests this, having found in some experiments that 100 grms. of water digested with phosphorus for sixty-four hours at 38·5° dissolved ·000127 grm. He also investigated the solvent action of bile, and found that 100 grms. of bile under the same conditions, dissolved ·02424 grm., and that the solubility of phosphorus rose both in water and bile when the temperature was increased. Phosphorus is somewhat soluble in alcohol and ether, and also, to some extent, in fatty and ethereal oils; but the best solvent is carbon disulphide. [271] _Zur acuten Phosphor-Vergiftung_, Dorpat, 1866. The following is the order of solubility in certain menstrua, the figures representing the number of parts by weight of the solvent required to dissolve 1 part of phosphorus:-- Carbon Disulphide, 4 Almond Oil, 100 Concentrated Acetic Acid,[272] 100 Ether, 250 Alcohol, specific gravity ·822, 400 Glycerin, 588 [272] Phosphorus is very little soluble in cold acetic acid, and the solubility given is only correct when the boiling acid acts for some time on the phosphorus. Phosphorus exists in, or can be converted into, several allotropic modifications, of which the red or amorphous phosphorus is the most important. This is effected by heating it for some time, in the absence of air, from 230° to 235°. It is not poisonous.[273] Commercial red phosphorus does, however, contain very small quantities of unchanged or ordinary phosphorus--according to Fresenius, from ·6 per cent. downwards; it also contains phosphorous acid, and about 4·6 per cent. of other impurities, among which is graphite.[274]