130 OXALIC ACID. 



Hydroxy-butyric acid. 1 CH 8 . CH (OH) . CH 2 . COOH. 



This acid is the next homologue to the lactic acids in the 

 glycolic series. It is frequently found in the urine of acute dia- 

 betes, usually accompanied by aceto-acetic acid [CH 8 . CO . CH 2 . 

 COOH]. The pure acid is sirupy and laevo-rotatory. (a) D = -23'4. 

 For its separation from urine and estimation see Kiilz 2 and 

 Stadelmann. 3 



OXALIC ACID SERIES. 

 Oxalic acid. (CO . OH),. 



This acid does not occur in the free state in the human body. 

 Calcium oxalate, however, is a not unfrequent constituent of urine, 

 and enters into the composition of many urinary calculi, the. so- 

 called mulberry calculus consisting almost entirely of it, and it is 

 very commonly found in urinary deposits. As ordinarily precipi- 

 tated from solutions of calcium salts by the addition of a salt 

 of oxalic acid, the calcium oxalate is usually amorphous. To 

 obtain it in the crystalline form dilute solutions of the two 

 reagents must be allowed to mix very slowly, as by diffusion. In 

 urine the case is different ; the oxalate is at first in dilute solution, 

 probably dissolved by the sodium dihydric phosphate (NaH 2 P0 4 ) 

 to which the acidity is normally due. On standing the urine 

 cools and the oxalate separates out in a crystalline form, viz. 

 rectangular octohedra, which is characteristic and striking, and 

 usually unlike that of any other constituent of urinary deposits. 



FIG. 4. CALCIUM OXALATE. (After Funke.) 



In some cases it presents the anomalous forms of rounded 

 lumps, dumb-beils, or square columns with pyramidal ends, but 

 these forms are uncommon. 



The crystals are insoluble in ammonia and acetic acid, but 

 readily soluble in hydrochloric or other mineral acid, also 

 slightly so in solutions of acid phosphates and urates of 



1 See Neubauer u. Vogel, Analyse d. Earns, 1890, S. 110. 

 a Zt.f. Biot. Bd. xxni. (1887), S. 329. 

 Ibid. S. 456. 



