The Elements of Chemistry (Muir)

The Elements of Chemistry was written by Matthew Moncrieff Pattison Muir and published in 1904. Muir was a Praelector and Fellow of Gonville and Caius College, Cambridge and head of their Caius Laboratory.

Sourced

• I hope I have not merely added one more illustrated catalogue of chemical odds and ends to the many which have already appeared under the title of A text book of Chemistry.
  • Preface

Ch.I Some of the Marks of those Changes the Elucidation whereof is the Object of Chemistry

Separation of substances into unlike parts by mechanical methods

• The "blue earth" of the diamond fields of South Africa is shaken with water, and the earthy matter, which sinks slowly, is poured off in the water; by repeating this process several times, the diamonds are obtained apart from the earth wherewith they were mixed in the material dug from the soil.
  • Separation of substances into unlike parts by mechanical methods

• The crude sulphur found in Sicily and other places is heated in pots, whereupon the sulphur melts and floats on the surface of the earthy matter which remains at the bottoms of the pots; the melted sulphur is poured into moulds, where it solidifies, and the earthy matter left in the pots is thrown away.

• In some parts of the East, sulphur is separated from the earthy matter wherewith it is mixed in the soil, by heating the crude material very strongly in earthen pots, each covered with another similar pot inverted on it. The sulphur melts and then becomes gaseous and the gaseous, sulphur condenses in the upper pots, which are comparatively cool; the fine yellow powder which condenses is approximately pure sulphur; the earthy impurities remain in the lower pots.

• The juice which is expressed from sugar-canes is boiled in vacuum-pans until it becomes thick, and is then allowed to cool, when crystals of sugar separate from it; the thick, dark-coloured, liquid which refuses to crystallise is drawn off and sold as molasses. This separation of the juice of the cane into two different substances is effected by making use of a property of sugar, namely its readiness to crystallise, and a property of molasses, namely, its inability to crystallise. These properties belong to the two substances whether they are or are not mixed.

• The upper layers of the soil in certain districts of India contain nitre [ or saltpetre ]; the nitre is separated from earthy matter by washing the soil with water, and evaporating the watery liquor until nitre separates therefrom. Nitre dissolves in water, and separates again in crystals when much of the water has been removed by evaporation; but ordinary soil is insoluble in water.

• One of the peculiar properties of gold is that it readily amalgamates, that is, forms an alloy, with mercury; when this amalgam is heated, the mercury is driven off as a vapour, and the gold remains: quartz is not affected by contact with mercury. Gold is sometimes separated from the quartz wherein it is found by making use of the behaviours of gold and quartz with mercury: the auriferous rock is crushed and mixed with mercury; the amalgam which is a liquid, is poured off from the quartz, and is separated into gold and mercury by heating; the mercury vapour is condensed, and the liquid mercury is used again.

• Petroleum-oil is a mixture of several liquids, each characterised by its own properties, one of which is its boiling-point. The oil can be separated into its constituent liquid substances by heating it in a vessel attached to a condenser, and fitted with a thermometer; the portions which distil at certain definite temperatures are collected separately, and each is again distilled. These processes are repeated until the various liquids, the mixture whereof is petroleum, have been separated from one another. This separation is effected by using a certain property peculiar to each constituent of the petroleum, namely, its boiling-point, as a means for removing each from the other constituents.

• The separations which have been described are... comparable with that whereby a fine powder is separated from a coarse powder by the use of a sieve. A property of the fine powder is that it passes through the meshes of the sieve; a property of the coarse powder is that it does not pass through the sieve; the powders retain these properties when they are mixed and are separated by making use these properties.

Changes of homogeneous substances

• Although homogeneous substances cannot be separated into unlike portions by any process of the nature of sifting or sorting, they can be changed into other homogeneous substances different from themselves.

• When water is dropped on to an exceedingly hot [2500º C] surface, the water (or some of it) disappears and two gases are produced which are entirely different from water and from one another.
  • See also water splitting & hydrogen production by thermolysis

• When a strong electric current is passed through melted salt, a light, shining, metal-like solid [ sodium ], and a yellow gas [ chlorine ], having a very penetrating odour, are formed in place of the salt.
  • See also electrolysis, Humphry Davy's discovery of new elements and chlorine & chlorine production by gas extraction

• When chalk is heated in a lime-kiln, a gas [ CO, in addition to CO₂ ], which is colourless, odourless, and poisonous, escapes from the top of the kiln, and lime is found in the hearth.
  • See also thermal decomposition

• When sulphur is burnt in the air, a suffocating gas is produced in place of the sulphur, which gradually disappears.
  • See also sulfur dioxide production)

• When red lead is heated, it is changed into litharge, and a gas [oxygen] wherein a lighted taper burns rapidly and brilliantly.

• When a diamond is very strongly heated in a stream of the gas [oxygen] obtained from red lead, it is changed into the gas [carbon dioxide] which is formed by heating chalk.

• When calcined mercury is raised to a high temperature, it is changed into mercury and the gas [oxygen] which is formed by heating red lead.

• The processes wherein homogeneous substances are changed into other homogeneous substances different from themselves are more far-reaching, more penetrating, than any process which can be described as sifting or sorting. These changes are so great that we cannot describe their characteristic features except by saying that one substance appears to be destroyed, and another, or others, to be formed.

• When iron is immersed in warm diluted oil of vitriol [ sulfuric acid ], the iron gradually disappears, gas [hydrogen] being given off as long as any iron is visible; when the liquid which is thus produced is evaporated, a greenish crystalline solid ferrous sulfate separates from it, and this substance has none of the characteristic properties either of iron or oil of vitriol. ...The new substance produced by this reaction is homogeneous, that is, by no process of sifting, sorting, or picking, has it been separated into unlike portions.

• When sulphur is heated in the air, it takes fire, and gradually burns away, and the sense of smell tells us that a penetrating, choking, and most objectionable gas [ sulfur dioxide ] is produced. This gas has none of the properties that characterise sulphur, and none of those that distinguish air from other substances. Sulphur is a yellow, crystalline, nearly odourless, solid which is insoluble in water; air is a colourless gas, without smell or taste, which is slightly soluble in water; the new substance is a colourless, strongly smelling, gas which dissolves very readily in water to produce a solution which has an acid taste and a marked odour. The new substance is homogeneous; it is produced by a reaction between sulphur and the air, but it is not separable into these substances... by any operation which can be described as sifting, sorting, or picking.

• It is a property of the system iron plus diluted oil of vitriol to change into another system, one component of which is a green solid with certain definite properties, and it is a property of the system sulphur plus air (at a certain temperature) to change into another system, one member of which is a colourless, badly smelling gas with certain definite properties. What has become of the iron, the sulphur, the diluted oil of vitriol, the air? These are chemical questions.

Other examples of changes of homogeneous substances

• When steam is passed over red hot iron, two other homogeneous substances are produced; one of these is a black solid, and the other is a colourless, very light gas. The system composed of steam and iron has changed into a system composed of magnetic oxide of iron and hydrogen.

• When nitre (potassium nitrate) is heated with oil of vitriol (sulphuric acid) as long as any change happens, both of these homogeneous substances disappear, and a system of homogeneous substances is produced composed of a white solid (sulphate of potassium), a colourless, very corrosive liquid (nitric acid), a colourless gas (oxygen), a reddish brown [toxic] gas (nitrogen dioxide with a sharp, biting odor] and water.

• When salt is heated with oil of vitriol until the reaction is finished, one system of homogeneous substances is changed into another system; in place of salt (sodium chloride) and oil of vitriol (sulphuric acid), there are found a white solid (sodium sulphate) and a fuming, strongly acid-smelling gas (hydrochloric acid).

• Equal masses of iron and cheese weigh the same, although they differ in all their other properties: all the substances which we class as different would appear identical to a being who could compare the weights of substances, but was unable to recognise any other properties of them.
  • Note on mass and weight

Characteristic features of chemical changes

• A chemical change is a change of certain homogeneous substances into certain other homogeneous substances: whatever masses of the original substances are brought into contact, the masses which interact are in a definite and unchangeable proportion to one another, and to the masses of the products of the change; and the sum of the masses of the substances which form the initial system is equal to the sum of the masses of the substances which form the final system.

• However different may be the properties of the products of a chemical reaction from the properties of the substances which reacted to form these products... the substances which are formed are formed by the union, or coalescence, or incorporation, of those which reacted.

Can all homogeneous substances be separated into unlike parts?

• No one of the four substances mercury, oxygen, sulphur, or iron, has been formed, or synthesised, by putting together two or more other substances; chalk and litharge have been formed, or synthesised, by uniting different substances chalk by combining lime and carbonic acid-gas [ carbon dioxide ], litharge, by combining lead and oxygen.

Two kinds of homogeneous substances. Elements and compounds.

• Whether a homogeneous substance is an element or a compound can be determined only by a series of quantitative experiments: if it has been separated into two or more homogeneous substances, and formed by the union of two or more homogeneous substances, it is a compound; if it has not been separated into unlike portions, nor formed by the union of unlike substances, it is an element.

Fuller examination of a few chemical changes

• What happens when iron changes to rust? A small muslin bag is filled with iron-filings which have been thoroughly wetted with water; the bag is hung on a stand and the stand is placed in a basin containing water, and is covered with a glass cylinder. An examination of the apparatus after 24 hours or so shows that the water has risen about one-fifth of the distance from the lower to the upper end of the glass cylinder, and the iron-filings are covered with rust. The air which now remains in the cylinder is about four fifths of the volume of the air which was in the cylinder when the experiment began. The air in the cylinder is transferred to a smaller cylinder of glass (standing in water) wherein wetted iron filings, free from rust have been placed; the water does not rise in the second cylinder, nor does the iron rust, even after several days. ...by inverting the second cylinder, and plunging a lighted taper into it; the taper is extinguished; but if the same taper is lighted, and plunged into a similar cylinder full of ordinary air, it continues to burn.

Fig.1 Lavoisier measures oxygen in formation of mercuric oxide

Fig.2 Lavoisier measures oxygen from thermal decomposition of mercuric oxide

• When mercury is heated nearly to its boiling point in air, it is very slowly changed to a red powder, which used to be called calcined mercury. Lavoisier made a quantitative study of this change. ...(Fig. 1) The mercury was heated nearly to its boiling point by a furnace; red specks appeared on the surface of the mercury, and the volume of air in the bell-jar gradually decreased. The production of the red solid seemed to cease after some days, but the heating was continued for a few days longer (12 days in all). The volume of air in the bell-jar at the end of the experiment was noted; the red solid was collected, and weighed, and placed in a small glass bulb... (Fig. 2). When the red solid was strongly heated, mercury appeared on the upper and colder parts of the glass bulb, and a colourless gas collected in the graduated vessel. The heating was continued until the whole of the red powder disappeared... An examination of the gas collected in the cylinder proved it to be the substance which is now called oxygen.

• Lavoisier's quantitative examination of the change... proved that the total mass of the reacting substances mercury and air, remained unchanged. ...the masses of the two elements which combine are always in the ratio of one of oxygen to 12.5 of mercury. When the compound mercuric oxide is strongly heated, it is changed into the elements mercury and oxygen; the sum of the masses of the two elements obtained is exactly equal to the mass of the compound changed; the masses of the mercuric oxide, mercury, and oxygen, are always in the ratio of 13.5 to 12.5 to 1.

Summary

• The constituents of certain substances retain... the properties or most of the properties which they have when they are separated from one another. Such substances can be separated into their constituents by sifting, sorting, or picking; they are said to be heterogeneous substances, or mixtures.

• There are other substances which cannot be separated into unlike portions by any process that can justly be described as sifting; these are said to be homogeneous substances.

• Chemistry is not directly concerned with heterogeneous substances. This branch of natural science examines the changes which happen when homogeneous substances interact.

Ch.II The Study of Composition the Laws of Chemical Combination

• The law of chemical change... includes two statements which are generally known as the law of fixity, or constancy, of composition, and the law of conservation of mass. The former states that the composition of every compound is constant; the latter asserts that the sum of the masses of all the substances concerned in a chemical process is constant.
  • Presentation of chemical changes in terms of the laws of combination

• The law of conservation of mass was first put into definite form by Lavoisier, in the eighties of the eighteenth century. ...The prolonged and exhaustive experiments of Stas proved the strict accuracy of the law of conservation of mass; the law is confirmed by every quantitative experiment made in chemistry.
  • Law of conservation of mass

• There is always a very simple relation between the volumes of homogeneous gases which react, and between these volumes and those of the gaseous products of the reactions. The generalisation may be expressed in this form: the volumes of the homogeneous gases concerned in any chemical change are always equal to, or small whole multiples of, the volume of one of the gases taken as unity.
  • Law of gaseous combination

• The laws of chemical combination may be accepted as veritable laws of nature they are the foundation of the science of chemistry.

Summary

• The composition of a compound is stated in terms of the elements which unite to form it, and can be obtained by its decomposition.

• The laws of chemical combination may be expressed in one statement, which asserts the fact that all homogeneous substances interact in the ratios of certain fixed masses, or in the ratios of whole multiples of these masses. We have agreed, provisionally, to call the smallest values which can be given to these fixed masses, in terms of hydrogen as unity, or of oxygen as eight times unity.

Notes to Chapter 2

• In... A New System of Chemical Philosophy published in 1808, John Dalton laid the foundations of the atomic theory: he assumed chemical action to be an action between very minute particles of elements and compounds, and all the minute particles of the same element, or compound, to be exactly the same size and weight. ...his hypothesis assumed the accuracy and universal applicability of those generalisations which are now called the laws of chemical combination.

External links

• Matthew Moncrieff Pattison Muir, The Elements of Chemistry (1904)