Urometer

UROMETER is a hydrometer designed specifically for testing the specific gravity of urine. The hydrometers (floats) of Geissler or Vogel used for this purpose are equipped with a scale on a thin, long neck with graduation marks from 1.000 to 1.040, which are spaced 1-1.5 mm apart from each other. The immersed part of the urometer is equipped with a thermometer marked with a red line indicating the temperature at which the instrument is calibrated. When determining the specific gravity of urine with such a urometer, either the urine is brought to this specially marked temperature, or for every 3 degrees of temperature above the one marked with the red line, 1° is added to the specific gravity read on the urometer, and conversely, the same amount is subtracted for each drop in the temperature of the tested urine by 3° below the temperature indicated on the scale by the red line. To achieve more accurate readings, specific gravities from 1.000 to 1.040 are distributed across 2 or 4 instruments. The scale of the urometer proposed by Heller has different divisions graduated according to Baumé. Heller's urometers present the inconvenience that the figures obtained with their help must be converted to the readings of the aforementioned hydrometer; each division of Heller's urometer corresponds to 7 divisions of Geissler's urometer. In addition, the instrument is less accurate. The source of errors when using a urometer is the capillarity of the instrument or its inaccurate calibration. To eliminate the latter, it is necessary to check each newly acquired hydrometer against a reliable standard or with a 0.2% sodium chloride solution, the specific gravity of which at 15° is 1.000. Lohnstein proposed a weight urometer to avoid errors arising from capillarity when using ordinary urometers. For clinical purposes, using an ordinary Vogel urometer is sufficient. To determine the specific gravity of urine using a urometer, carefully (to avoid foaming) fill a cylinder up to ⁴/₅ of its capacity with urine, into which a clean and dry urometer is immersed, and read off the scale to what degree it has sunk. A temperature correction is then applied. The cylinder must be wide enough so that the urometer does not touch its walls.