Page images
PDF
EPUB
[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

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. 75 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.

[blocks in formation]

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.

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

compound a, 1 : 1 in b.

=

1: 2 in

Iodides of mercury. c. ws. of iodine: c. ws. of mercury = 1:2 in compound a, 1:1 in b.

Sulphides of copper. c. ws. of sulphur : c. ws. of copper in compound a, 1:1 in b.

=

1:2

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; N,, two c. ws. of nitrogen; N,, three c. ws. of nitrogen; generally N x c. ws. of nitrogen: let O represent one c. w. of oxygen; 0, x 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 ;

:

[ocr errors]

Oxides of nitrogen. ON, ON, ON, ON

ვ.

Oxides of chromium. O Cr, Cr, OC, O Cr1, O̟ ̧Cr.
Chlorides of antimony. CISb, C1 Sb.

Bromides of tin. BrSn,, BrSn.

Iodides of mercury. Iнg,, IHg.

Sulphides of copper. SCu,, SCu.

CHAPTER VI.

SYMBOLS AND FORMULAE.

76

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.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

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

« PreviousContinue »