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These numbers represent parts by weight of each element which combine with 8 parts by weight of oxygen, 16 of sulphur, or 35.5 of chlorine; in other words these numbers represent the parts by weight of each element which combine with one combining weight of oxygen, or sulphur, or chlorine.

The conception of combining weight may be extended to all the elements. The combining weight of an element which forms a compound with hydrogen must be regarded by us at present as a number expressing the mass of the element which combines with unit mass of hydrogen. The combining weight of an element which does not form a compound with hydrogen we shall for the present regard as the mass of that element which combines with one combining weight of oxygen, or of sulphur, or of chlorine; i.e. with that mass of oxygen, sulphur, or chlorine, which combines with unit mass of hydrogen, i.e. with 8 parts by weight of oxygen, 16 of sulphur, or 35.5 of chlorine.

The laws of multiple, and reciprocal, proportions may now be put into one statement.

The elements combine in the ratios of their combining weights, or in ratios which bear a simple relation to these.

To illustrate this mode of expressing the laws of multiple and reciprocal proportions, let us tabulate (1) the combining weights of several elements, (2) the compositions of several compounds of these elements stated as so many combining weights of each element.

Combining weights of some elements.
A.

B.
Determined from composition Determined from composition of
of compounds with

compounds with elements in hydrogen.

column A.
Nitrogen = 4:6

Chromium= 17:46
Oxygen = 8

Tin = 295
Sulphur = 16

Copper = 31.7
Chlorine = 35.5

Antimony = 40
Bromine = 80

Mercury = 100
Iodine = 127
Composition of some compounds; stated as number

of combining weights of each element.
Oxides of nitrogen. c. ws. of oxygen : c. ws. of nitrogen =1:1

in compound a, 1:3 in compound b, 2:3 in compound c, 4:3 in compound d.

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CHAPTER VI.

SYMBOLS AND FORMULAE.

176

It is customary to express the composition of compounds in a kind of shorthand by a method the principle of which is the same as that we are at present illustrating.

A symbol is given to each element; this symbol is formed either of the first letter, or of the first and some other letter, of the name of the element. When the names of several elements begin with the same letter that element which has been longest known and best studied generally gets a symbol formed of the first letter only; but there is no universally applicable rule. Some of the symbols are derived from the names by which the elements were known to the ancients or in the middle ages. The symbols of two elements, potassium (K), and sodium (Na), are derived from the names kalium and natrium by which these elements are known to German chemists. The symbol W is given to the element tungsten, it is derived from the name (Wolfram) of the mineral from which tungsten was first obtained.

It is of the utmost importance to remember that each of these symbols represents a definite mass of the element; it represents either one, two, three, four, five, or six, combining weights, as we are at present using the term combining weight, of the element. The following table gives the names and symbols of the elements.

Elements.

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137

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Os

193

Bi

O

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194

12

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Mass of

Mass of element

element Name. Symbol. expressed

Name.

Symbol. expressed by sym

by symboll

boll Aluminium

27 Molybdenum Mo
Antimony Sb 120 Nickel Ni
Arsenic As 75 Niobium Nb 94
Barium

Nitrogen

14 Beryllium

Osmium Bismuth 208 Oxygen

16 Boron

11 Palladium Pd 106 Bromine 80 Phosphorus

31 Cadmium

112 Platinum Pt Caesium 133 Potassium K

39 Calcium

40 Rhodium Rh 104 Carbon

Rubidium Rb 85.4 Cerium 140 Ruthenium

104.6 Chlorine

Ci
35.5
Scandium

44 -
Chromium
52.2 Selenion

79 Cobalt

59 Silicon Copper

Cu 63.2 Silver Didymium Di 144 Sodium

23 Erbium

166 Strontium Fluorine

19
Sulphur

32
Gallium
69.9 Tantalum

182 Germanium

72.2 Tellurium Te 125 Gold 197 Terbium

148 Hydrogen H 1 Thallium

204 Indium 113.4 Thorium

232 Iodine : 127 Tin

118 Iridium 192.6 Titanium

48 Iron 56 Tungsten

184 Lanthanum 139 Uranium

240 Lead Pb 207 Vanadium

51.2 Lithium

Yttrium Magnesium Mg

Ytterbium Yb 173 Manganese Mn 55 Zinc

Zn 65 Mercury Hg

Zirconium Zr 90 1 The values in this table are given in round numbers ; they are only

Si

28

108

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