Make a hypobromite solution by dissolving 100 parts of caustic soda in 250 parts of water, and adding when cold 25 parts of bromine. Keep the bromine separate until the test is made, as the solution must be fresh.

The test depends on the fact that urea mixed with alkaline hypobromites is decomposed and yields nitrogen, from the amount of which gas the quantity of urea is estimated. The necessary apparatus consists of a tube in which the urine is placed (four or five times as much of the solution being added), and a pneumatic trough with a measuring tube graduated to show the amount of nitrogen gas. ‡

Fowler's Test based on the loss of specific gravity, is easier of application. The specific gravity of the urine is carefully determined as well as that of the liq. sodae chloratse (U. S. P.) to be used. One volume of the urine is mixed with exactly seven volumes of the liquor chloride of soda, and set aside for two hours, or until effervescence ceases. The specific gravity is again taken. As the reaction begins immediately on mixing the fluids, the specific gravity of the mixture must be calculated. This is done by adding to the specific gravity of the urine seven times that of the liquor chloride of soda, and divide the sum by eight. Each degree of difference in specific gravity of the mixture before and after the decomposition represents three and a half grains of urea to the fluid ounce of the day's urine.