i6o THE JOURNAI, OF PHARMACOLOGY. 



2. Solutions containing uric acid, when added to Fehling's solution, 

 which must not be in excess, cause a white precipitate, which consists of a 

 combination of copper suboxide and uric acid, to form. If an excess of 

 Fehling's solution is used, red suboxide of copper forms and the uric acid 

 is partially oxidized into allantoin. 



3. Microscopic (see later, under urinary sediments). 



Quantitative Determination. 



If the sample contains albumin this must first be removed (see albumin). 

 In case the sample is very dilute it may be concentrated to about one-half 

 of its original volume, say 400 cc. to 200 cc. 



If a sediment of uric acid or urates appears in the sample, it must be 

 brought into solution. This can be done by immersing the container in 

 hot water. After cooling, the required quantity of urine can be measured 

 ofiF. If, as sometimes happens, the uric acid again separates out upon 

 cooling, the sample may be diluted with distilled water. The degree of 

 dilution practiced must of course be taken into account in all subsequent 

 calculations. 



I. Method of Heintz-Schwanert. 



200 cc. of clear urine are placed in a beaker and 5 cc. of hydrochloric 

 acid added. Stir well with a glass rod and set aside in a cool place for 

 36-48 hours. The crystals of uric acid which by this time have separated 

 out are collected on a previously dried and weighed filter, and washed with 

 cold water (using as little of this as possible), to remove hydrochloric acid. 

 After washing, dry at about 100° C, and weigh. The increase in weight 

 represents uric acid. Uric acid is not entirely insoluble in cold water, 

 therefore a part of it goes into solution during the washing. The filtrate 

 and washings should on this account be collected and for each 100 cc, 

 ,0048 gm. may be added to the quantity as obtained above. The quantity 

 thus obtained multiplied by 7^^ will give the daily excretion. This 

 method, even when the correction is applied is not a very accurate one, 

 although easily carried out. The results in any case are only approximate. 

 In place of the paper filter (which in each case must be thoroughly dried 

 and preferably weighed in a weighing bottle or well stoppered test tube), a 

 glass wool or asbestos filter may be used. The use of a filter pump, besides 

 hastening filtration, facilitates the subsequent operation of drying. 



( To be cofitinued. ) 



