Estimating the specific gravity of a few drops of urine has always been a difficult problem. This difficulty arises more particularly during ureteral catheterization, when only a few drops of urine can be obtained. By the method described here, the specific gravity of a few drops of urine from each kidney can be determined. It will be found applicable in estimating the specific gravity of small samples of voided urine.
This method for the determination of the specific gravity of urine is made possible by the utilization of a non-water-soluble mixture. We use for this purpose a mixture of a high specific gravity chemical (carbon tetrachloride), and a low one (xylene). It can be prepared quickly and cheaply from materials ordinarily at hand in the laboratory.
Hammerschlag1 has adapted this principle to determine the specific gravity of blood. But he has used a mixture of chloroform and benzine.
John Kirkpatrick, David H. Kling. A SIMPLIFIED METHOD FOR DETERMINATION OF THE SPECIFIC GRAVITY OF A FEW DROPS OF URINE. JAMA. 1926;87(7):487–488. doi:10.1001/jama.1926.92680070001009