400 ESTIMATION OF URIC ACID. 



deposits. Ammonium urate occurs iu very small quantity in a deposit of "urates," 

 but is formed in considerable amount when urine becomes ammoniacal from decom- 

 position (fig. 261). Free uric acid occurs in normal urine only in the very smallest 

 amount. It is sometimes deposited after a time (fig. 260). It frequently forms 

 urinary calculi and gravel. 



The urine of newly-born children contains much uric acid. Uric acid and its salts are 

 increased after severe muscular exertion, accompanied by perspiration, in catarrhal and rheu- 

 matic fevers, and such conditions as are accompanied by disturbance of the respiration ; in 

 leuka>mia and tumours of the spleen, cirrhotic liver, and generally in cases of catarrh of the 

 stomach and intestinal tract, following the excessive use of alcohol. [It is also increased 

 during ague and fevers, and perhaps this has some relation to the congestion of the spleen which 

 accompanies these conditions.] It is diminished after copious draughts of water, after large 

 doses of quinine, caffein, potassic iodide, common salt, sodic and lithic carbonates, sodic sul- 

 phate, inhalation of 0, slight muscular exertion. In gout, the amount excreted in the urine 

 is small. In chronic tumours of the spleen, anaemia, and chlorosis, when the respiration is not 

 at the same time embarrassed, it is also diminished. 



Urates. Uric acid forms salts chiefly acid urates with several bases, which 

 dissolve with difficulty in cold water, but are easily soluble in warm water. Neutral 

 urates are changed by C0 2 into acid salts. Hydrochloric and acetic acids break 

 up the compounds, and crystals of uric acid separate. 



(1) Acid sodic urate usually appears as a brick-red deposit in urine ; more rarely grey or 

 white (lateritious deposit), tinged with uroerythrin, in catarrhal conditions of the digestive 

 organs, and in rheumatic and febrile affections. Microscopically, it is completely amorphous, 

 consisting of granules, sometimes disposed in groups (fig. 260, b) sometimes the granules have 

 spines on them. The corresponding potash salt occurs not unfrequently under the same con- 

 ditions, and presents the same characters. 



(2) Acid ammonium urate (fig. 261, a) always occurs as a sediment in ammoniacal urine r 

 either with (1), or mixed with free uric acid, accompanied by triple phosphate. Microscopically, 

 it is the same as (1). (1) and (2) arc distinguished by the sediment dissolving when the urine is 

 heated. If a drop of hydrochloric acid be added to a microscopic preparation of the sediment, 

 crystals of uric acid separate. 



(3) Acid calcic urate occurs sometimes in calculi, and is a white, amorphous powder slightly 

 soluble in water. When heated on platinum it leaves an ash of calcium carbonate. Magnesium 

 urate rarely occurs in urinary calculi. 



259. ESTIMATION OF URIC ACID. I. Qualitative. 1. Microscopic Char- 

 acters. The appearances presented by uric acid and its salts under the microscope. 

 It is deposited from urine after several hours, on adding acetic or hydrochloric acid. 



2. Murexide Test. Gently heat a urate or uric acid in a porcelain vessel along 

 with nitric acid. Decomposition takes place and the colour changes to yellow. N 

 and COo are given off ; urea and alloxan (C 4 H 2 N 2 4 ) remain. Evaporate slowly 

 and allow the yellowish-red stain to cool ; on adding a drop of dilute ammonia a 

 purplish-red colour of murexide is obtained, it becomes blue on the addition of caustic 

 potash. If potash or soda be added instead of ammonia, a violet colour is obtained. 



3. Schiff's Test. Dissolve uric acid or a urate in a solution of an alkaline carbonate, and 

 drop it upon blotting-paper saturated with a solution of silver nitrate, reduction of the silver 

 takes place at once, and a black spot is formed. 



4. On boiling a solution of uric acid or a urate in an alkali, with Fehling's solution ( 149, 2), at 

 first white urate of the suboxide of copper is deposited, while later, red copper suboxide is formed. 



II. Quantitative Estimation. Add 5 cubic centimetres of concentrated HC1 to 100 c.c. of 

 urine, and allow it to stand for forty-eight hours in the dark, when the uric acid is precipitated 

 like tine cayenne pepper crystals. All the uric acid is not precipitated by the HC1, even after 

 standing for a time. [E. A. Cook uses sulphate of zinc to precipitate the uric acid as urate of 

 zinc. Caustic soda is added to precipitate the phosphates, and then to the clear fluid zinc sul- 

 phate solution, which precipitates urate of zinc as a white gelatinous deposit.] 



Fokker-Salkowski Method. Make 200 c.c. of urine strongly alkaline with sodic carbonate, 

 and after an hour add 200 c.c. of a concentrated solution of ammonium chloride, whereby acid 

 urate of ammonium is precipitated. After forty-eight hours filter, through a small weighed 

 filter, and wash it several times. Fill the filter with dilute HC1 and collect the filtrate. Do this 

 until all the acid urate is dissolved. From the total filtrate after a time all the uric acid separates. 

 It is collected in the same filter, washed with water and alcohol until the acid reaction dis- 

 appears, dried at 100 C. and weighed. To the weight in excess of the filter add 0'030 grm. 



