an instrument that is used to determine the quantity of hemoglobin in the blood. In practice the hemoglobinometer proposed in 1902 by the Swiss scientist H. Sahli is used. It is based on comparison of the color of the tested blood, which is treated with hydrochloric acid, with the color of standards. In the USSR the GS-2 model of hemoglobinometer is produced. It consists of two color standards and test tubes with two calibrations to determine hemoglobin in gram percent and percent (100 percent corresponds to 16 gram percent; each gram corresponds to 6 percent). In many countries hemoglobinometers are used in which 100 percent on the scale corresponds not to 16 gram percent, but to 14.8 gram percent, 17.3 gram percent, and so forth. When blood is treated with a hydrochloric acid solution, the hemoglobin is converted to hematin hydrochloride, and the solution turns brown. The solution in the test tube is diluted by gradually adding distilled water until the color of the solution is the same as that of the standard. The quantity of hemoglobin is determined by reading the level of the solution on the scale of the test tube.

The amount of hemoglobin in the blood can be determined by the gasometric method, according to the quantity of absorbed oxygen or carbon dioxide gas, or by the chemical method, which is based on the determination of iron in the hemoglobin molecule. Although these methods are more accurate than the hemoglobinometer, they are not widely used because of their laboriousness. Photoelectrospectrometry is used to standardize the hemoglobinometer.