75

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 no 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.

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

29.5
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.

A.

=

Oxides of chromium. c. ws. of oxygen : c. ws. of chromium = 2:3

in compound a, 8:9 in b, 1:1 in c, 4:3 in d, 2:1 in e. Chlorides of antimony. c. ws. of chlorine: c. ws. of antimony=1:1

in compound a, 5:3 in b. Bromides of tin, c. ws. of bromine : c. ws. of tin 1:2 in

compound a, 1:1 in 6. Iodides of mercury:

c. ws. of iodine : c. ws. of mercury = 1:2 in compound a, 1:1 in 6. Sulphides of copper. c. ws. of sulphur : c. ws. of copper 1:2.

in compound a, 1:1 in b.

The composition of all compounds may be stated in this way. Let us use a symbol to represent one combining weight of an element. Let N represent one combining weight of nitrogen; Ng, two c. ws. of nitrogen; Ng, three c. ws. of nitrogen; generally N X c. ws. of nitrogen : let O represent

of
oxygen ;

Ö

2 c. ws. of oxygen : Cr, one c. w. of chromium : Sb, one c. w. of antimony: Sn, one c. w. of tin: Hg, one c. w. of mercury : Cu, one c. w. of copper : Cl, one c. w. of chlorine : Br, one c. w. of bromine: I, one c. w. of iodine: and S, one c. w. of sulphur. Then the compositions of the above compounds may be represented thus ;

Oxides of nitrogen. ON, ON2, O, N, ON
Oxides of chromium. 0,Crą, o Cr, Cr, Ö, Cry, 0Cr.
Chlorides of antimony. ŚCISb, &L Sb,
Bromides of tin. BrSn, BrSn.
Iodides of mercury. IHS, IHg.
Sulphides of copper. SCu

,

SCu.

one c. W.

3

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.

31

Co

59

Mass of

Mass of element

element Name. Symbol. expressed Name. Symbol. expressed by sym

by syinboll

boll Aluminium Al 27 Molybdenum Mo 96, Antimony Sb 120 Nickel

Ni 58.6 Arsenic As 75 Niobium Nb 94 Barium

Ba 137 Nitrogen N 14 Beryllium

Be

9 Osmium Os 193 Bismuth Bi 208 Oxygen O

16 Boron

B
11 Palladium Pd

106
Bromine Br 80 Phosphorus P
Cadmium Cd 112 Platinum

Pt

194 Caesium Cs 133 Potassium K 39 Calcium Ca 40 Rhodium Rh

104 Carbon

С

12 Rubidium Rb 85.4 Cerium

Ce 140 Ruthenium Ru 104.6 Chlorine Ci 35.5 Scandium Sc 44 Chromium Cr 52.2 Selenion Se 79 Cobalt

Silicon

Si 28 Copper Cu 63.2 Silver

108 Didymium Di 144 Sodium

Na 23 Erbium

Er 166 Strontium Sr 87 Fluorine F 19 Sulphur S

32 * Gallium Ga 69.9 Tantalum Ta 182 Germanium Ge 72.2 Tellurium

Te

125 Gold

Au 197 Terbium Tr 148 Hydrogen H 1 Thallium

204 Indium

In 113.4 Thorium Th 232
Iodine
I 127 Tin

118 Iridium

Ir

192.6 Titanium Ti 48 Iron

Fe 56 Tungsten W 184 Lanthanum La 139 Uranium U 240 Lead

Pb

207 Vanadium V 51.2 Lithium Li

7 Yttrium

Y 89 Magnesium

Mg

24 Ytterbium Yb 173 Manganese Mn 55 Zinc

Zn 65 Mercury Hg 200 Zirconium Zr

90 i The values in this table are given in round numbers; they are only approximately correct.

Ag

ΤΙ

Sn

68