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2 AsC1, + 3H,0 + Aq = As, O,Aq + 6HCIA.
BCI, + 3H2O + Aq = H BO,Aq + 3HClAq.
PBr, + 3H 0 + Aq = H PO Aq + 3HBrAq.
2SBr, + 3H,0 + Aq=H_SO, Aq +39 + 4HBrAq.

25e,1 + 3H2O + Aq = H SeÒ, Aq + 3Se + 4HIA.
In some cases the products of the interaction of a non-
metallic haloid compound and water are HX and a compound
of the non-metal with oxygen and halogen; thus

l SbI+H,O + Aq=SbOI + 2HIAą. Most of the haloid compounds of the metallic elements are chemically unchanged when brought into contact with water; several dissolve in water. In some cases however chemical change occurs; the usual products are haloid compounds of hydrogen (HX) and an oxychloride, oxybromide, or oxyiodide, of the metal :--thus,

BiCl + 2H 0 + Aq = BioCl + 2HCIAT;

2SnCl, + H,0+ Aq = Sn,OCI, + 2HCIA. Interactions with water. The three elements dissolve in 157 water, chlorine very freely, bromine less freely, and iodine only in small quantities. By cooling aqueous solutions of chlorine or bromine crystals separate having the composition Cl.5H,0 and Br.5H.O respectively: no hydrate of iodine-i.e. compound of iodine with water-has been obtained. Aqueous solutions of the three elements contain small quantities of hydrochloric, hydrobromic, and hydriodic acids, respectively; i.e. the water and chlorine &c. interact as shewn by the equation

2X + H,0 + Aq=2HXAq +0. This reaction proceeds more rapidly when X=Cl than when X = Br. When X = I but very little reaction occurs. These reactions are hastened by sunlight. If some easily oxidised substance is dissolved in water and chlorine is passed into the liquid the substance is usually oxidised; thus a solution of sulphur dioxide reacts with chlorine to produce sulphur trioxide, a solution of phosphorous oxide reacts with chlorine to produce phosphoric oxide :—or, in equations

(1) SO, Aq+H,0 + 2Cl = 2HClAq + SO,Aq.

(2) P,O,Aq + 2H,0 +4Cl = 4HCIAq+P,0 Aq. The bleaching action of chlorine depends upon its interacting with water to produce oxygen. Dry chlorine does not bleach a piece of madder-dyed cloth ; but if water is present

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143

BEFORE proceeding further with the examination of the properties of classes of elements and compounds with the view of tracing connexions between changes of composition and changes of properties we must acquaint ourselves with the system of nomenclature used in chemistry.

Many names of elements, and such names of classes of compounds as oxides, hydrides, &c. have been incidentally employed.

A name is given to each element. Sometimes the name expresses a characteristic chemical or physical property of the element; e.g. oxygen=acid-producer, hydrogen=water-producer, bromine, because of its powerful and obnoxious smell (Bpwuos), iodine, because of the violet colour of its vapour (iwons), chromium, because of its many-coloured compounds (xowua). Sometimes the name is that which was used by the ancients or is a modification of this name; e.g. arsenic (apo evikov), copper (cuprum). Sometimes the name is derived from the name used by the alchemists, many of which were derived from the names of the planets; e.g. mercury. The names of many recently discovered elements are derived from the names of the minerals from which they were first obtained, or from the names of the districts, or in some cases countries, in which these minerals were found ; thus strontium (from the mineral strontianite found near the village of Strontian in Argyleshire), beryllium (from the mineral beryll), ytterbrium, yttrium, erbium (from Ytterby the district in Sweden where the minerals were found from which the three elements were obtained), gallium, germanium (the former was discovered by a French, the latter by a German, chemist).

Some names are purely fanciful; e.g. tellurium, selenion, uranium, vanadium, (from tellus = the earth, oelnun = the

moon, the planet Uranus, and the Scandinavian deity Vanadis, respectively). The names of the more recently discovered metals all end in um.

The name given to a compound expresses the qualitative 144 composition of that compound; if more than one compound of the same elements is known, names are given indicative of the relative quantities of the elements which unite to form reacting weights of the compounds.

The name of every compound of two elements ends in ide. Thus all compounds of oxygen with one other element are called oxides. The variety of oxide is indicated by prefixing the name of the element united with oxygen; thus we have iron oxides, zinc oxides, sulphur oxides, &c.

Similarly we have sulphides, i.e. compounds of sulphur with one other element; chlorides, i.e. compounds of chlorine with one other element; bromides, fluorides, hydrides, &c. &c. We say hydrogen oxide, hydrogen chloride, hydrogen sulphide; not oxygen hydride, chlorine hydride, sulphur hydride: oxygen, chlorine, and sulphur, are all more negative, or more nonmetallic, elements than hydrogen. The name of the more negative of the two elements of a binary compound is changed into a qualifying term ending in ide. Thus it is better to say oxide of chlorine-or chlorine oxide—than chloride of oxygen (or oxygen chloride).

When two oxides, chlorides, &c. of one element are known, the general custom is to form an adjective from the name of the element other than oxygen, &c. and to modify the termination of this adjective so as to express that one compound is composed of more, or less, oxygen, relatively to a fixed mass of the other element, than the other compound is. A comparison of the following names with the composition of each compound as expressed by its formula will illustrate this method of naming pairs of oxides, &c. of the same element. Iron oxides

Sulphur oxides
Ferrous oxide Feo

Sulphurous oxide SO,
Ferric Fe,Og.

Sulphuric
Chromium chlorides

Tin bromides
Chromous chloride CrCl, Stannous bromide Sn Br,
Chromic

Crcl Stannic
Copper sulphides
Cuprous sulphide Cus
Cupric

Cus.

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Sn Br

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The termination -ous always indicates less of the nonmetallic or negative element than the termination -ic, relatively to the same mass of the metallic or positive element.

When more than two oxides, &c. of the same element are known, two methods of naming are adopted. Four oxides of bismuth are known. Their compositions, and the names given to each, are as follows:

Hypobismuthous oxide; or Bismuth dioxide Bi,o
Bismuthous oxide; or Bismuth trioxide

Bi o Hypobismuthic oxide; or Bismuth tetroxide Bi, o Bismuthic oxide; or Bismuth pentoxide

Bio
Five oxides of nitrogen are known :
Nitrous oxide; or Nitrogen monoxide NO
Nitric oxide

NO
Nitrogen trioxide

N.O
Nitrogen tetroxide NO

Nitrogen pentoxide NO One oxide gets the termination-ic; another, with relatively less oxygen, the termination -ous; the prefix hypo- is used to express relatively less oxygen than that of the -ic or -ous oxide. The prefix per- is sometimes employed to designate that oxide of a series which has relatively most oxygen.

Or the number of combining weights of oxygen in a reacting weight of each oxide is expressed by the prefixes mono, di, tri, &c. Unfortunately neither system is very strictly carried out. We shall have further examples of each system as we proceed.

The composition of one oxide of series is sometimes expressed by a name formed from the names of other two oxides of the series ; thus FeO is ferrous, Fe,0, is ferric, and Fe,O, is ferroso-ferric, oxide.

The name sesquioxide is frequently used; it implies that a positive element and oxygen are united in the ratio of 1:11 combining weights; thus Fe,O, is often called iron sesquioxide, Cr, O, chromium sesquioxide, &c.

Acidic oxides are sometimes named so as to indicate the acid obtained by interaction of each with water; thus SO, is called sulphuric anhydride, because it interacts with water to produce sulphuric acid. On this system of naming, the term anhydride means an acidic oxide. Lastly an oxide, chloride, &c. is sometimes distinguished from another oxide, chloride, &c. of the same element by a term indicating some prominent

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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,O, Chromo-chromic oxide.

Cr 0Chromic oxide; Chromium sesquioxide; Green oxide of chromium.

Chromium dioxide; Brown oxide of chromium. Cro Chromium trioxide; Chromiumi 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
HSO, Sulphuric

HCIO Chloric

HCIO, Perchloric Nitrogen acids.

Phosphorus acids. HNO Hyponitrous acid. H PO

Hypophosphorous acid, HNO, Nitrous

H POZ Phosphorous
HNO, Nitric

H PO
HPO

Phosphoric
HP ON

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