248 POISONS I THEIR EFFECTS AND DETECTION. [§ 305 . 
hot water, and then add a drop of a solution of mercuric nitrate and 
mercurous nitrate, when a rose colour is at once developed, if the tyrosin 
is in very minute quantity ; but if in more than traces, there is a distinct 
crimson precipitate. To separate leucin and tyrosin from the urine, the 
best process is as follows :—The urine is filtered from any deposit, 
evaporated to a thin syrup, and decanted from the second deposit that 
forms. The two deposits are mixed together and treated with dilute 
ammonia, which will dissolve out any tyrosin and leave it in needles, if 
the ammonia is spontaneously evaporated on a watch-glass. The urine 
is then diluted and treated with neutral and basic acetates of lead, filtered, 
and the l&ad thrown out of the filtrate by hydric sulphide. The filtrate 
is evaporated to a syrup, and it then deposits leucin mixed with some 
tyrosin. If, however, the syrup refuses to crystallise, it is treated with 
cold absolute alcohol, and filtered ; the residue is then boiled up with 
spirit of wine, which extracts leucin, and deposits it on cooling in a 
crystalline form. To obtain oxymandelic acid, the mother-liquor, from 
which leucin and tyrosin have been extracted, is precipitated with 
absolute alcohol, filtered, and then the alcoholic solution evaporated to a 
syrup. This syrup is acidified by sulphuric acid, and extracted with 
ether ; the ether is filtered off and evaporated to dryness ; the dry residue 
will be in the form of oily drops and crystals. The crystals are collected, 
dissolved in water, and the solution precipitated by lead acetate to remove 
colouring-matters ; after filtration it is finally precipitated by basic 
acetate. On decomposition of the basic acetate, by suspending in water 
and saturating with hydric sulphide, the ultimate filtrate on evaporation 
deposits colourless, flexible needles of oxymandelic acid. The nitro- 
genised acid which Schultzen and Riess obtained from urine in a case of 
phosphorus poisoning, was found in an alcohol and ether extract—warts 
of rhombic scales separating out of the syrupy residue. These scales gave 
no precipitate with basic acetate, but formed a compound with silver 
nitrate. The silver compound was in the form of shining white needles, 
and contained 33-9 per cent, of silver ; the acid was decomposed by heat, 
and with lime yielded aniline. Its melting-point is given at from 184° 
to 185°. The occurrence of some volatile substance in phosphorus 
urine, which blackens nitrate of silver, and which is probably phosphine, 
was first noticed by Selmi. 1 Pesci and Stroppa have confirmed Selmi ; s 
researches. It is even given off in the cold. 
§ 305. The quantitative estimation of phosphorus is best carried 
out by oxidising it into phosphoric acid, and estimating as ammon. 
magnesian phosphate. To effect this, the substances are distilled in an 
atmosphere of C0 2 into a flask with water, to which a tube containing 
silver nitrate is attached ; the latter retains all phosphine, the former 
solid phosphorus. If necessary, the distillate may be again distilled into 
1 Oiornale Internaz. della Scienza Med., 1879, Nro. 5, p. 645. 
