Natural. Dry Residue. Urea 3.010 44.70 Lactic acid, lactate of ammonia,} 1.714 25.58 and extractive matter } Uric acid 0.100 1.49 Mucus 0.032 0.48 Sulphate of potash 0.371 5.54 Sulphate of soda 0.316 4.72 Phosphate of soda 0.294 4.39 Biphosphate of ammonia 0.165 2.46 Chloride of sodium 0.445 6.64 Muriate of ammonia 0.150 2.46 Phosphates of magnesia and lime 0.100 1.49 Silica 0.003 0.05 Water 93.300 ------- ------ 100.000 100.00 Among the special organic constituents of the urine are three substances, urea, uric acid, and hippuric acid, which are of much importance in a manurial point of view. The first of these is found in considerable quantity in the urine of all animals, but is especially abundant in the carnivora. Uric acid is found only in these animals, and is the most remarkable constituent of the excrement of birds, serpents, and many of the lower animals. Hippuric acid is most abundant in the herbivora. These substances are all highly nitrogenous. They contain-- Urea. Uric Acid. Hippuric Acid. Carbon 20.00 36.0 60.7 Hydrogen 6.60 2.4 5.0 Nitrogen 46.70 33.4 8.0 Oxygen 26.70 28.2 26.3 ------ ----- ----- 100.00 100.0 100.0 They are extremely prone to change, and in presence of animal matters readily ferment, and are converted into salts of ammonia. Thus human urine, which, at the time of emission is free from smell of ammonia, and has a slightly acid reaction, becomes highly ammoniacal if it be kept for a few days. This is due to the conversion of urea into carbonate of ammonia; and the same change takes place, though more slowly, with uric and hippuric acids.