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physical character, usually colour; thus one sometimes speaks of the brown oxide of chromium, the black, or the magnetic, oxide of iron.

The various systems of naming binary compounds are summarised in the following examples.

Sulphur oxides. SO Sulphurous oxide; Sulphur dioxide; Sulphurous anhydride.

So, Sulphuric oxide; Sulphur trioxide; Sulphur peroxide;
Sulphuric anhydride.

Chromium oxides.
Cro Chromous oxide.
Cr, Chromo-chromic oxide.

Cro Chromic oxide; Chromium sesquioxide; Green oxide of chromium.

Cro, Chromium dioxide ; Brown oxide of chromium.

Cro Chromium trioxide; Chromium peroxide; Chromic anhydride ; Red oxide of chromium.

The nomenclature of many compounds of three or more 145 elements is based on the relations which exist between acids and salts. To each acid is given a name indicative, as far as possible, of its composition. Prefixes and terminations are used as in the naming of binary compounds. Thus all acids obtained by combining sulphur with hydrogen and oxygen are called sulphur acids; those formed by the combination of chlorine with hydrogen and oxygen are called chlorine acids; those produced by uniting nitrogen with hydrogen and oxygen are called nitrogen acids; and so on.

The following examples shew how one acid is distinguished
from others of the same series.
Sulphur acids.

Chlorine acids.
H SO, Hyposulphurous acid. HCIO Hypochlorous acid.
H SO, Sulphurous

HCIO. Chlorous
H S Sulphuric

HCIO; Chloric

HCIO, Perchloric
Nitrogen acids.

Phosphorus acids.
HNO Hyponitrous acid. H PO, Hypophosphorous acid.
HNO, Nitrous

H POZ Phosphorous
HNO Nitric

HPO Phosphoric

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The three acids H PO,, HPOZ, H,P,0, are all called phosphoric acid because they are all obtainable from the same oxide or anhydride, P,0s. The composition of the acid formed by the interaction of this oxide with water varies according to the relative masses of the interacting compounds, and the temperature; thus

(1) P,0, +H,O (cold) = 2HPO
(2) PO +26,0 (cold) =H PO,

(3) PO: +3H hot) = 2 PO
That acid of the three from which the greater number of well
known and stable salts are obtained, viz. H PO,, is called ortho-
phosphoric acid (óptos = right or true); the acid HPO, may be
obtained from H. PO, by removing water (H, PO, -H,O=HPO.),
it is generally called metaphosphoric (metà implies change of
composition); the third acid HP O, may be produced by
heating H, PO, (2H,PO, heated = 8,8,0, +7,0), it is called
pyrophosphoric acid.

The names of the salts obtained from a given acid by causing
it to interact with metals, basic oxides, or alkalis, are derived
from the name of the acid; each salt is distinguished from
others by the name of the metal or metals which form part of
its composition. Thus the salts obtained from sulphurous
acid are called sulphites, those from sulphuric acid are called
sulphates, and so on.
Hypochlorous acid; HCIO, Chlorous acid; HCIO,
KCIO Potassium hypochlorite. AgC10 Silver chlorite.
NaC10 Sodium

Pb2010, Lead
Perchloric acid; HCIO
Ba(C10), Barium perchlorate.
RbC102 Rubidium perchlorate.

Sulphuric acid; H SO,
Iron sulphates.

Mercury sulphates.
Feso Ferrous sulphate. Hg,SO, Mercurous sulphate.
Fe,350, Ferric

HgSo, Mercuric
Nitric acid; HNOz.
Tin nitrates.

Iron nitrates.
Sn2NO, Stannous nitrate.

Fe2NO, Ferrous nitrate.
Sn4NO, Stannic

Fe3NO; Ferric These examples shew the use of the adjectival form of the name of the metal, and the meaning of the terminations -ous


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and -ic, in naming salts. A salt whose name ends in -ous is composed of less of the non-metallic elements, relatively to a fixed mass of the metal, than a salt of the same acid and the same metal whose name ends in -ic.

Ternary compounds (compounds of three elements) which 147 are not salts, as we are using this term, are generally named on the same principle

as that which guides the nomenclature of binary compounds. Thus BioCl is called bismuth oxychloride; BiSci, bismuth sulphochloride ; HgBrl, mercury bromoiodide, or i odobromide.

The nomenclature of carbon compounds cannot be discussed 148 here ; suffice it to say that a name is usually given to each class of these compounds and that the individual members of this or that class are distinguished according to their composition. Thus, as we have a large class of acids, so we have a class of carbon compounds shewing certain common properties and certain well marked analogies in composition called alcohols; to another group of carbon compounds the name aldehydes is given; and so on.

M. E. C.





We have now gained some fairly clear notions of the methods adopted in chemistry for classifying elements and compounds. Similar elements are put into the same class. Similar elements are those which interact with other elements and with compounds under similar conditions to produce similar compounds.

Compounds again are said to be chemically similar or analogous when their compositions and their properties are similar.

The questions to be answered with regard to any element before its position in a scheme of chemical classification can be determined are such as these ;-Does the element combine with oxygen? Under what conditions are its oxides formed ? What is the composition of each of these oxides? Are its oxides basic or acidic? Does it combine with hydrogen ? What is the composition of its hydride or hydrides? Does it form any acids ? Under what conditions are these acids produced, and what are their compositions and properties? Does it interact with acids to form salts? What are the products of its interaction with water? Or is it unchanged when brought into contact with water or steam? Does it form chlorides, bromides, oxychlorides, &c. ? Under what conditions are these compounds produced? What are their compositions, and how do they interact with other bodies ?

As chemistry is the study of the connexion between changes of composition and changes of properties, the subject of classification must be all important in chemistry. We must therefore proceed to examine a few classes of elements that we may learn how answers are gained to such questions as these just proposed, and what kind of answers they are which are gained.

The three elements chlorine, bromine, iodine, are placed in 150 the same class.

gases; air=1.


Chlorine, Bromine. Iodine. Combining Weights. 35.5


127 Specific gravities as


Specific gravities as
gases; hydrogen=1. 35.5

80 Specific gravities as solids or liquids; water=1.

3.18 (liquid) 4.94 (solid) Melting points ( (approxi

- 220

1150 Boiling mate). points

--- 350


above 2000 Appearance and pro- Yellow-green gas, Dark-reddish- Grey, lustrous minent physical pro- liquified at 00 black liquid; solid; vapour is perties,

under pressure of solidifying at deep violet
6 atmos. to a yel- about – 25o to colour. Odour
low, very refrac- reddish-brown less marked
tive, liquid. Very crystals. than that of

the two other

strong; rapidly elements.

corrodes ani- Poisonous.
mal aud vege-
table tissues.

Odour very

Occurrence. None of these elements is found uncombined 151 with others. The commoner compounds are those with sodium, potassium, calcium, and magnesium. Chloride, bromide, and iodide of potassium, sodium, calcium, or magnesium occur in sea water, in mineral waters, and in some rocks. Chlorides of some or all the metals named are widely distributed; bromides occur in smaller quantities; and iodides, with iodates (salts of the acid HIO), are found only in very small quantities.

Preparation. Sodium (or potassium) chloride, bromide, or 152 iodide, is mixed with manganese dioxide and sulphuric acid, and the mixture is heated; manganese sulphate, sodium sulphate, water, and chlorine, bromine, or iodine, are formed. Putting X as = Cl, Br, or I, the change may be thus expressed ;2NaX + 2H SO, + MnO, = MnSO, + Na SO, + 2H,0 + 2X.


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