THE ORGANIC CONSTITUENTS OF THE URINE. 243 



Aside from its occurrence in solution and in urinary sediments, oxalic 

 acid is also not infrequently found to constitute the greater portion 

 of renal and vesical calculi. 



Quantitative Estimation of Oxalic Acid. DUNLOP'S METHOD 

 (modified by Baldwin). Five hundred c.c. of a well-mixed specimen 

 of the twenty-four hours 7 urine are treated with 150 c.c. of over 90 

 per cent, alcohol, to precipitate the oxalate of calcium. After forty- 

 eight hours the crystals are collected on a filter, thoroughly washed 

 with hot and cold water and with dilute acetic acid (1 per cent.). The 

 filter is placed in a small beaker and soaked in a small amount of 

 dilute hydrochloric acid. It is then washed with hot water until 

 there is no further acid reaction. The washings are filtered and 

 evaporated to about 20 c.c. A very little calcium chloride solution 

 is added to insure an excess of calcium. The hydrochloric acid is 

 neutralized with ammonia and the solution then rendered slightly 

 acid with acetic acid. Strong alcohol is now added to the amount 

 of 50 per cent, of the volume of the fluid and the solution set aside 

 for forty-eight hours. The sediment is collected on a filter that is 

 free from ash, and washed with cold water and dilute acetic acid until 

 free from chlorides. (Hot water should here be avoided, as it carries 

 the finely divided precipitate through the pores of the filter.) The 

 filter is incinerated over a Bunsen burner, and afterward heated in 

 the blowpipe-flame. The residue is allowed to cool over sulphuric 

 acid and weighed. The ash is calcium oxide, each gramme of which 

 corresponds to 1.6 grammes of oxalic acid. 



The urine in every case should be thymolized as soon as possible, 

 to prevent fermentation and the precipitation of phosphates. If the 

 specimen is alkaline, it is rendered slightly acid with acetic acid. 



The method is applicable in the case of human urine, but in 

 that of dogs with a high specific gravity it is very difficult to remove 

 the phosphates. In such an event SalkowskVs method is best 

 employed. 



SALKOWSKI'S METHOD. If the urine is concentrated (sp. gr. 

 1.040-1.050), it is treated with 20 c.c. of hydrochloric acid (sp. gr. 

 1.12) for 200-250 c.c., and extracted in a separating funnel three 

 times with alcoholic ether (5-10 per cent, alcohol). The ethereal 

 extract is filtered through a dry filter, the ether is distilled off, the 

 remaining fluid evaporated to 20 c.c., and filtered on cooling. The 

 filtrate is rendered alkaline with ammonia, and is then treated with 

 12 c.c. of a 10 per cent, solution of calcium chloride and acetic 

 acid. The process is continued as described. 



With human urine larger quantities, such as 500 c.c., are em- 

 ployed, which are first concentrated to about one-third of their 

 original volume. 



Allan toin. 



Allantoin is a normal constituent of the urine of man, as also 

 of various animals, but is usually present only in traces in the 



