, 1 ( IDS . I XI) 11 ) DROX \ \i CIDS. 
615 
To demonstrate the presence of oxalic acid, ami to estimate Lts amount, a 
litre of urine should be treated with calcium chloride and ammonia, and 
afterwards made acid with acetic acid. After twenty-four hours' standing, 
the crystalline precipitate, which contains uric acid crystals mixed with 
calcium oxalate, is filtered off and treated with dilute hydrochloric acid. The 
oxalate dissolves, and is reprecipitated, after filtering off the uric acid, by the 
addition of ammonia. At a dull red heat it is converted into calcium 
carbonate, and may be weighed as such. 
Fig. 56. — Calcium oxalate. 
Acids and hydroxyacids of the fatty series, with derived 
substances. — Normal urine contains minute quantities of the volatile 
fatty acids, especially acetic, but also formic, propionic, and butyric 
acids. 1 They do not, as a rule, amount collectively to more than some 
50 mgrms. in the day's excretion, and they arise doubtless from the 
bacterial decomposition of carbohydrates and proteids in the lower 
bowel. Fatty acids of low atomic weight, such as the above, are less 
easily oxidised in the organism than are those of greater complexity. 2 
The amount is considerable in the urine of herhivora, and in man it is 
increased by many diseases, especially by such as lead to increased decomposi- 
tion in the bowel, or to prolonged constipation. 
When a specimen of urine undergoes ammoniacal fermentation, the 
volatile acids are increased at the expense of the carbohydrates it contains. 3 
These acids are obtained from the urine by distillation with phosphoric 
J Cf. v. Jaksch, Zlschr. f. physiol. C'/iem., Strassburg, 1886, Bd. x. S. 536. The 
earlier literature is here summarised. 
-<_'. Schotten, ibid., 18S3, Bd. vii. S. 375. 
"Salkowski, ibid., 1S89, Bd. xiii. S. 264. 
