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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.
compounds with elements in hydrogen.
Tin = 295
Copper = 31.7
Antimony = 40
Mercury = 100
of combining weights of each element.
in compound a, 1:3 in compound b, 2:3 in compound c, 4:3 in compound d.
SYMBOLS AND FORMULAE.
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.
Mass of element
element Name. Symbol. expressed
Symbol. expressed by sym
27 Molybdenum Mo
Osmium Bismuth 208 Oxygen
11 Palladium Pd 106 Bromine 80 Phosphorus
112 Platinum Pt Caesium 133 Potassium K
40 Rhodium Rh 104 Carbon
Rubidium Rb 85.4 Cerium 140 Ruthenium
59 Silicon Copper
Cu 63.2 Silver Didymium Di 144 Sodium
166 Strontium Fluorine
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
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