CHEMISTRY. It is impossible in this article to do more than briefly describe some of the most important of the numerous changes Which have been introduced into the science of chemistry within the last few years.
1. The system of measuring temperature, lengths, weights, and volumes has been altered. The centigrade has completely superseded the Fahrenheit thermometric scale in all recent chemical works, and the French metric (which is a decimal) system has been adopted for all measurements and weights, inches and their fractions being replaced by 10ths or 100ths of a meter, and grains by grams. It has this advantage over all the other systems, of possessing one fundamental linear unit, from which all the ramifi cations of linear, superficial, or solid dimensions, and of weight are derived. See METER, LITER, GRAM, FRANC. This unit is the 10-millionth part of a quadrant of the meridian, or of the distance from the pole to the equator. It is only to measures of weight and capacity or volume that we need here refer. "Multipt,y," says Dr. Hof man in his energetic appeal in favor of the metric system, " the cubic meter by one million, and you have a fit measure in terms of which to express the capacity of the Atlantic, or its cubical contents of brine; divide the cubic meter by one million, and you arrive at the petty volume of the gambler's ordinary die."—Ifodern, Chemistry, P. 124. This last-named volume, the millionth of a cubic meter, taken as so much distilled water at a temperature of 4° C. (its point of greatest density), furnishes the metrical unit of weight called the gram, which thus forms a link connecting weight with meas ure. Again, dividing the edge of a ?rider cube, which is a linear meter, into 10 parts, called decimeters, and cubing one of these parts, we obtain a unit of volume or capacity to which the term liter is applied. The various weights in use are all multiples or divi sions by tens. Thus, 10 meters form a decameter, 100a hectometer, and 1000 a kilo meter; while of a meter is called a decimeter, a centimeter, and a millimeter, the Greek prefixes in all cases denoting multiplication, and the Latin divi sion. The reader will do well to recollect the following rough comparisons between the chief French and English measures chiefly used in chemistry, as otherwise he can form no conception of the length, size, or weight of the substances treated of A meter = nearly 1.1 linear yard = 39.37 in.; a millimeter = 0.039, or nearly it th of an in. ; a centi meter = 0.39, or nearly 5th of an in.; and a decimeter = 3.94, or nearly 4 in.; a gram = 15.43 gr.; and a liter = rather more than 61 cubic in., or a pint and three-quarters. The accompanying figure represents a cubic decimeter. Two of the edges of the front side are divided, as may be seen, into 10 linear centimeters: and the space occupied by a cubic centimeter is shown on the upper right-hand corner of the tube. Now, a
cubic decimeter is employed as a unit for measures both of weight and of volume, for in the former capacity it contains, at 4° C., 1 kilogram, or 1000 grams of dis tilled water, and in the latter it loses its name of kilogram and receives the appel lation of liter, which corresponds to 1000 cubic centimeters, or iaaath of a cubic meter. Chemists have long felt the want of an appropriate volume, with its corresponding weight, to serve as standard units of measurement, and prof. Holman has selected 1 cubic decimeter = 1 liter, as the most appropriate unit of volume, and the weight of this measure of pure hydrogen as the unit of weight, hydrogen being taken at 0° C. temperature, and 0rP76* pressure. To this standard weight-unit, which = 0.0896 of a grain, he assigns the name of crith, from the Greek krithe, a barley-corn, signifying figuratively a small weight; and the weight is now in universal acceptation amongst modern British chemists. There is probably no figure in chemical science more impor tant than this one (0.0S96 of a gram) to be remembered and kept ready for calcula tion; for it is the standard multiple or co-efficient by means of which the weight of 1 liter of any other gas, simple or compound, is computed. "For example, the relative volume-weight of chlorine being 35.5, that of oxygen 16, and that of nitrogen 14, the actual weights of 1 liter of each of these elementary gases at 0° C. and 0n176 pres sure, may be called respectively 35.5 criths, 16 criths, and 14 criths. So again with reference to the compound gases, the relative volume-weight of each is equal to half the weight of its product-volume. Hydrochloric acid (HC1), for example, consists of 1 volume of hydrogen 1 volume of chlorine = 2 volumes, or by weight, 1 + 35.5 = 36.5 units; whence it follows that the relative value-weight of hydrochloric acid gas is 36.5 = 18.25 units; which last figure therefore expresses the number of criths which 1 liter of hydrochloric acid gas weighs at 0° C. and 0m76 pressure, 18.26 X 0.0896 = 1.6352 as the actual weight in grams of hydrochloric acid gas. Again, as the product-vol ume of water gas (H20),1 taken at the above temperature and pressure, contains 2 vol umes of hydrogen + 1 volume of oxygen, and therefore weighs 2 + 16 = 18 units, the single volume of water-gas weighs = 9 units, or substituting as before the concrete 2 for the abstract value, 1 liter of water-gas weighs 9 criths; that is to say. 9 X 0.0896 gram = 0.8064 gram."—Op. cit. p. 131. In concluding this subject we will only further remark, that when a closely approximative result suffices, the crith may be esti mated at 0.09 gram.