Degree

DEGREE, a conventional unit used in the measurement of the most diverse quantities, for example: temperature, hardness, acidity, salinity, strength; a degree as a unit of measurement for angular quantities, a geographical degree, etc. Temperature degree is a conventional difference in temperatures, depending on the choice of scales for a thermometer. At the present time, three scales are commonly used. 1. In the Réaumur scale, the basic points are the melting point of ice, taken as zero, and the boiling point of water, taken as 80° (changes in the volume of mercury occurring between these two points are evenly divided into 80 separate parts, and 1/80 of the increase in volume between points 0 and 80 corresponds to 1° Réaumur). 2. In the Celsius thermometer, the expansion of mercury between the boiling point of water and the melting point of ice is conventionally divided into 100 parts (1/100 of the increase in mercury volume between these points corresponds to 1°). 3. Fahrenheit scale. The 0° point of Celsius and Réaumur corresponds to 32° in Fahrenheit, the boiling point of water corresponds to 212°; the space between 32° and 212° is divided in Fahrenheit into 180 parts. (Used mainly in England and America.) For precise work, one must account for the not entirely uniform expansion of liquids from which thermometers are usually constructed, and therefore the degree of an air thermometer is taken as the basis for the thermometric scale. This degree corresponds to the expansion of a gas by 1/273 of its initial volume or, which is the same, an increase in the elasticity of the gas by 1/273 of its initial value. Previously, various gases were used, since the expansion of all gases is very close to one another (see Gay-Lussac's Law). At the present time, for scientific experiments, either a thermometer in which the expanding body is hydrogen is used, or—for lower temperatures—helium. With such thermometers, one can conduct research down to the lowest temperatures, which are only 1° from absolute zero; on the other hand, one can go up to very high temperatures necessary in modern technology. P. Lazarev. Degree of hardness, a conventional unit for denoting the degree of water hardness, which depends on lime and magnesium salts dissolved in the water. German, French, and English degrees of hardness are distinguished: 1° German corresponds to a content of 0.01 g of CaO in 1 liter of water; 1° French—0.01 g of CaCO3 in 1 liter of water; 1° English—0.014 g of CaCO3 in 1 liter of water. If hardness is caused by magnesium salts, then to calculate the degree of hardness, one converts the magnesium salts to an equivalent amount of calcium salts according to the equation: 1 part MgO = 1.4 parts CaO. In view of the fact that German, French, and English degrees of hardness are not equal to each other, the following table is usually used to convert one degree to another: 1° of German hardness = 1.79° French = 1.25° English. 1°

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= 1.43° French. Drinking waters having a hardness of less than 10 German degrees are classified as 'soft' waters; waters with a hardness of 10–20 German degrees are considered 'moderately hard'; waters above 20 German degrees are 'hard'. However, such a division has a very conventional sanitary significance, and in many cases, it is more expedient to make a sanitary assessment of water regarding its suitability in terms of hardness not according to a general scheme, but by conforming to local conditions. The most accurate method for determining the degree of water hardness is the gravimetric method, i.e., the quantitative gravimetric determination of calcium and magnesium salts contained in 1 liter of water. Volumetric analyses according to the methods of Clark, Winkler, Blacher, Wartha-Pfeiffer, and others, which are common in sanitary practice, are inferior in their accuracy to the gravimetric method.