482 QUALITATIVE AND QUANTITATIVE ESTIMATION OF URIC ACID. 



QUALITATIVE AND QUANTITATIVE ESTIMATION OF URIC ACID. 



Qualitative Estimation. i. The microscopic demonstration of uric acid and the 

 urates is based upon the characteristics that have been described. Uric acid is 

 precipitated from urine by addition of acetic or hydrochloric acid. 



2. The murexid test. Uric acid or urates are heated in a shallow dish with 

 nitric acid at a low temperature. Decomposition takes place, with the develop- 

 ment of a. yellow color. Nitrogen and carbon dioxid escape, while urea and 

 alloxan (C 4 H 2 N 2 O 4 ) remain behind. Evaporation is now cautiously carried 

 further, and the resulting yellowish-red stain is permitted to cool. The addition 

 of a drop of dilute ammonia produces a purple-red color (murexid = ammonium 

 purpurate: alloxantinamid) . This red color becomes blue on further addition of 

 potassium hydrate. If, at the outset, potassium or sodium hydrate is added to 

 the stain, instead of ammonia, a violet color results. 



3. If upon a strip of filter-paper saturated with a solution of silver nitrate 

 is dropped uric acid or urate dissolved in an alkaline carbonate, a black stain 

 at once appears through reduction of the silver. 



Quantitative Estimation. i. The method of Hopkins, by means of which the 

 uric acid is precipitated as ammonium urate. If 100 cu. cm. of urine are thor- 

 oughly saturated with ammonium chlorid (about 30 grams are necessary), all of 

 the uric acid is precipitated as ammonium urate, particularly if some ammonia 

 is added besides. After the lapse of two hours the precipitate is collected upon a 

 filter, where it is washed several times with a saturated solution of ammonium 

 chlorid. The precipitate is now rinsed from the filter with boiling water, and 

 exposed to the action of hydrochloric acid with heat. The uric acid that sepa- 

 rates is collected upon a dry filter, and is again dried and weighed. 



2. The method of Salkowski, modified by E. Ludwig, is based upon the pre- 

 cipitation of the uric acid by silver nitrate and its subsequent separation and 

 weighing. The following solutions are necessary : A . Twenty-six grams of silver 

 nitrate dissolved in water, and admixed with ammonia, until complete solution 

 takes place; then addition of water to make i liter. B. Magnesia-mixture: 100 

 grams of crystallized magnesium chlorid dissolved in water; ammonia added until 

 a strong odor is developed; then ammonium chlorid to the solution; and, 

 finally, addition of water to make i liter. C. Ten grams of pure sodium hydrate 

 dissolved in i liter of water. One-half of this is completely saturated with hydro- 

 gen sulphid, and then both halves are mixed. 



Mode of Procedure. One hundred cubic centimeters of filtered non-albumin- 

 ous urine (if necessary freed of albumin) are placed in a beaker. In another glass, 

 10 cu. cm. of the solution A are mixed with 10 cu. cm. of the solution B, and 

 ammonia is added, if necessary also ammonium chlorid to the point of complete 

 saturation. This solution is poured with stirring into the urine, and the mixture 

 is permitted to stand for one hour. The precipitate is then collected upon a 

 filter, is washed with water containing ammonia, and is brought, by means of a 

 pipette and a glass rod, without injury to the filter, back again into the beaker. 

 Now 10 cu. cm. of the solution C, diluted with 10 cu. cm. of water, are heated to 

 the boiling-point, and this solution is passed through the used filter into the beaker 

 which contains the silver-precipitate; the filter is then washed with hot water, 

 and the beaker is heated for some time over the water-bath with stirring. On 

 cooling, the solution is filtered into a dish; the filter is washed with hot water; 

 the filtrate is acidulated with hydrochloric acid; and the product is evaporated to 

 about 15 cu. cm., when 15 drops of hydrochloric acid are added, and the solution 

 is permitted to stand for twenty-four hours. The uric acid separated out is col- 

 lected upon a previously weighed filter, washed with water, alcohol, ether, and 

 hydrogen sulphid; dried at a temperature of 100 and weighed. For every 10 cu. 

 cm. of the watery filtrate, 0.00048 gram of uric acid are to be added. 



KREATININ, XANTHIN-BASES, OXALURIC, OXALIC, AND HIPPURIC 



ACIDS. 



Kreatinin (C 4 H 9 N 3 O 2 ) is derived in part from the kreatin present in 

 the muscles by loss of water, and in part from the meat in the food. Its 

 amount daily is from 0.6 to 1.3 grams. 



The amount of kreatinin is diminished in cases of progressive muscular atrophy, 

 of tetanus, and of marantic, anemic, or paralytic conditions of the musculature. 



