Chapter XL: Appendix: B.--The Decimal System

The metrical system of weights and measures, and the Centigrade thermometer scale have been generally used throughout the book, as more international and scientific than the complicated systems still unfortunately in use in this country. They have been fully explained in the Author’s ‘Laboratory Book,’ p. 2; but as this is not always at hand, a short sketch may be permitted here.

The basis of the metrical system is the “meter,” which is approximately ¹⁄₁₀,₀₀₀,₀₀₀ of the distance from the earth’s pole to the equator, and is equal to 39·3708 English inches, and for many practical purposes may be roughly reckoned as 40 inches. The meter is divided into 10 parts or “decimeters,” 100 parts or “centimeters,” and 1000 parts or “millimeters.” The standard of capacity is a cube of 1 decimeter, or about 4 inches, and consequently contains 1000 cubic centimeters, and is denominated a “liter.” The standard of weight is 1 cubic centimeter of water (at 4° C.), which is called a “gram.” Hence 1 liter of water weighs 1 “kilogram,” or 1000 grams. 1 cubic meter of water contains 1000 liters, and weighs 1000 kilograms, or 1 metrical ton (2200 lb. English). For purposes of reduction, the following figures may be given:--

1 gram = 15·431 grains. 1 lb. av. = 453·6 grams.

1 liter = 0·22 gallon. 1 gallon = 4·543 litres.

Actual reduction is, however, generally unnecessary if the question be treated as one of proportion. Thus a solution of 1 gram per liter is of the same strength as one of 1 lb. per 100 gallons (1000 lb.), and very approximately, as one of 1 oz. avoirdupois per cubic foot. In the case of pits, it is often simplest to measure them directly with a meter rule; length, breadth and depth, measured in decimeters and multiplied together, giving the contents in liters, and, in the case of water, the weight in kilograms.

The Centigrade or Celsius thermometer divides the difference between the freezing and the boiling points of water into 100°. The following table gives the points at which its scale agrees without fractions with that of Fahrenheit:

COMPARISON OF CENTIGRADE AND FAHRENHEIT DEGREES.

°C. °F.
-20 -4
-15 +5
-10 14
-5 23
0 32
5 41
10 50
15 59
20 68
25 77
30 86
35 95
40 104
45 113
50 122
55 131
60 140
65 149
70 158
75 167
80 176
85 185
90 194
95 203
100 212
105 221
110 230
115 239