A fair quantity of the urine, after shaking, should be placed in a tall conical glass vessel, to allow easy collection of the precipitate for subsequent, microscopical examination.  If an abundant amorphous deposit of a fawn or pink—­from uroerythrin—­color slowly settles and is readily diffused, urates in excess can be anticipated.  Their presence is proved by the readiness with which they dissolve on warming with the supernatant urine to about the temperature of the blood.  No difficulty is experienced if small quantities of albumen are present, as that body is not coagulated until the temperature rises much higher.  A sandy precipitate of free uric acid will not dissolve on warming the urine, and its identity can further be determined by means of the microscope, or by applying a well-known color-reaction.  A grain or so is oxidized into reddish alloxan and alloxantin by carefuly evaporating with a few drops of strong nitric acid on a piece of porcelain.  A little ammonia is then added, when the fine purple murexide stain will be produced.

It is always advisable to mention the reaction to test papers of all samples received.  Urine is normally acid, but there are certain diseases which render fluid neutral or alkaline.  The urea of acid urine on standing is changed by a putrefactive ferment into ammonic carbonate, but this decomposition in a state of health should not take place for at least twenty-four hours.  Alkalies, or organic salts of alkaline metals, when taken as medicine render the urine alkaline, and the indication is then not of much moment; but if none of these causes exist, the condition is of serious diagnostic import.  Where it is desired to determine the degree of acidity of the urine voided, say, by a gouty patient, a dilute volumetric solution of caustic soda should be employed, using a few drops of an alcoholic solution of phenolphthalein as an indicator, and reporting in terms of oxalic acid.  The soda solution may conveniently contain the equivalent of one milligramme of recrystallized oxalic acid (H_{2}C_{2}O_{4}.2H_{2}O) in each cubic centimeter.

UREA.

Carbamide, as it is called by systematic chemists, or urea, is next to water the largest constituent of urine, and forms about one-third of its total solids.  Derived from ammonic carbonate by abstracting two molecules of the elements of water, it is readily converted by putrefaction into that salt, and the urine under these circumstances becomes strongly alkaline in reaction.  Earthy phosphates then fall naturally out of solution, so that the putrid fluid is always well furnished with sediment.  Nitrogen that has served its purpose as muscle or other proteid leaves the animal economy chiefly in the form of urea, and its proportion in the urine, therefore, is a fair index of the activity of wasting influences.