By density is meant the specific gravity of the urine, which is determined by an instrument for the purpose, called a urinometer. As the density of urine varies considerably during the twenty-four hours, being particularly great an hour or two after meals, the test should be applied to the whole amount of urine secreted in the twenty-four hours.

When this cannot be done, the first urine passed in the morning should be tested. The specific gravity of the urine in health is 1.015 to 1.025; when the urine is very abundant in quantity and of light color, its specific gravity is usually low; when scanty and high colored, the density is high. When the specific gravity is habitually as low as 1.006 to 1.012, and the quantity of urine secreted is not excessively large, it is probable that the patient is suffering with Bright's disease. In case the density is habitually 1.030 or more, and the quantity of urine is large, chronic diabetes may be suspected, and the urine should be examined for sugar. The specific gravity of the urine, of course, depends upon the amount of solid matter it contains. The more nearly it approaches to 1.000, the less excrementitious matter it contains. The approximate amount of solid matter in the urine can be ascertained by simply doubling the last two figures obtained in testing the specific gravity; for example, if the specific gravity is 1.025, the urine contains about fifty grains of solid matter in one thousand of urine.