By what means do chymists effect a change in the qualities or states of natural bodies?

It is generally effected by means of heat*, or by the mixture† of some other matter with the matter intended to be examined‡. How does the application of beat and mixture enable chymists to examine the properties of bodies?

By these means chymists effect the decomposition of compound bodies, and thus acquire a knowledge of the nature of the ingredients of which they are composed§.

necessary to discover the means of analysing these substances, and of ascertaining wherein their difference consists. This we find in chymical re-agents. It may be considered as an axiom in the science of which we are treating, that whenever chymical action takes place, a real change is produced in the substance operated upon, and that its identity is destroyed. An example will place this in a clear point of view. If a little whiting be put into a glass of water, the whiting will sink to the bottom of the vessel. Though it should be mixed with the water, if left at rest it will soon subside. No chymical action has taken place; therefore the water and the whiting both remain unaltered. But if a little whiting be put into a glass of diluted sulphuric acid, a violent effervescence will commence the moment they come in contact with each other; a chymical union of the two substances will be the consequence of this chymical action; the identity of each substance will be destroyed; and sulphate of Time (a body entirely different to either of the substances employed) will be produced.

* Heat has a tendency to separate the particles of all bodies from each other. Hence nothing more is necessary to effect the decomposition of many bodies than to apply heat to them, and to collect the substances which are separated by that means. The mixture of two or more compounds often produces a decomposition in each by means of chymical affinity, a property of bodies which will be more fully explained hereafter.

It is owing to the laws of affinity that we are enabled to examine natural bodies by means of re-agents, or chymical tests. Some of these are simple, and act by single affinity; others, which are compound, act by producing a double decomposition.-See Chap. xiii.

Some idea of this mode of examination may be given by the following experiment :-Take camphor, which is a solid substance, put it into a phial half filled with spirits of wine; in a short time the camphor will be dissolved in the fluid, and the spirit will be as transparent as at first. This solution is owing to the affinity which subsists between these two substances. If water be now added (which has a greater affinity for the spirit than the camphor has) the water will unite with the spirit, and the camphor will be precipitated. In this way the camphor may be nearly all recovered, as at first. By distillation the water may also be separated from the spirit, and exhibited in a sepa

rate state.

This is called analysis. It is distinguished by chymists into the simple and the complicated analysis. The former is effected whenever a body is so decomposed that its elements may be exhibited in a separate state, and by reuniting them the body may be reproduced, Where the elements of a body form new compounds during its decomposition, and cannot be reunited to Ance a similar substance to that, which has been operated upon, it is an of complicated analysis.

to ascertain the exact nature of bodies, chymists have recourse to well as analysis. Whenever the component parts of any body are

What is meant by decomposition?

In chymical language decomposition means the act of dividing a body into its simple elements*. Thus water may be decomposed, and reduced into oxygen and hydrogen, which are simple substances, incapable of further decomposition.

What are the different states of natural bodies?

All bodies are either solidt, liquid, or aëriform‡.

reunited in order to form a similar substance, and a similar substance is produced, the nature of that body is said to be proved by synthesis. When a body admits of being examined in both these ways, the result is very satisfactory.

The examination of those substances which we receive from the hand of nature, if conducted on these principles, may sometimes be tedious, but the consequences will be pleasing; the processes may be slow, but they will be sure; and the acquisition of truth, by patient investigation, and by means of our own exertion, affords to a cultivated mind the most delightful gratifi-

cation.

*Take sulphate of magnesia (Epsom salt) as an instance of the decomposition and re-formation of a substance by chymical means. Make a solution of this salt in hot water, and pour into it a little of a solution of carbonate of soda; the soda will precipitate a white powder, which, on examination will be found to be carbonate of magnesia. When settled, decant the supernatant liquor, evaporate it till a pellicle rises on its surface, and set it aside to crystallize. When cold, crystals of sulphate of soda (Glauber's salts) will be found in the vessel. In this decomposition, the sulphuric acid of the Epsom salt combines with the soda to form sulphate of soda, and the carbonic acid of the soda combines with the magnesia to form carbonate of magnesia. In this way Epsom salt may be analysed, and proved to consist of sulphuric acid and magnesia.

In order to prove the composition of this salt by synthesis, dissolve magnesia in diluted sulphuric acid, saturate the liquor, and crystallize. Epsom salt will be the result.

It may be remarked, that chymists have not only the power of decomposing natural bodies, but of producing, by combination, various other substances, such as are not presented to us by the hand of Nature. Alcohol and ether are of this class.

We have many reasons for believing the original particles of all matter to be impenetrably hard, both from experiment and the necessity of the case, that nature might be incapable of wearing out. If water falls through a vacuum on metal, or on any hard body, it will strike it with as loud a noise as if one piece of iron fell upon another, A small instrument, which is sold by the mathematical instrument makers, called a water hammer, shows this very satisfactorily.Mr. Walker.

The force of cohesion increases in a substance in proportion as its moleculæ are brought nearer together. Thus alumine, which has shrunk considerably in bulk, by being submitted to a high degree of heat, has not only experienced much mechanical cohesion, but has thereby acquired the power of resisting acids and alkalies.-Berthollet's Chymical Statics, vol. 1, 3.

When attraction prevails in bodies they become solid; when caloric prevails they become gas: fluidity seems to be a medium between the two. The ultimate particles of matter existing in these separate states escape the cognizance of our senses. They are so infinitely small, as not only to escape the scrutiny of the highest magnifying powers in glasses, but even imagina

What do you mean by a solid body?

Solidity is that quality of bodies whereby their parts cohere firmly, so as to resist impression*.

What are liquid substances?

Liquid substances are those whose parts do not cohere firmly, but have free motion among themselvest.

What occasions the difference in these bodies?

Liquid substances are nothing more than solids converted into

tion itself is incapable of forming any idea of the size of an original particle of matter. When we have reduced matter to the most impalpable powder, we are far, very far, from the atoms which compose that powder. Musk, camphor, and several essences, will exhale for weeks, and throw off their particles to the distance of several yards, without losing any sensible weight.—(Mr. Walker's Lectures.) Even gold, when dissolved in aqua regia, assumes a gaseous state, with a small degree of heat. How minutely must the gold be divided by the acid, for its particles to exhale in atmospheric air!

A new theory, to account for the phenomena of matter, has been proposed by the celebrated Boscovich, and admitted by many philosophers An account of this system may be seen in the Supplement to the Encyclopædia Britannica, under the article Boscovich.

Sir Isaac Newton has said, that the primary particles of all bodies are bard, whether solid or fluid; and that if the particles be so disposed or fitted to each other as to touch in large surfaces, such body will be hard, otherwise it will be soft.

Perhaps it would be more philosophical to say, that when the attraction of aggregation is strong enough to resist the motion of the particles of a body among themselves, that body will be solid, otherwise it will be soft.

Mr. Lavoisier has explained solidity thus :-" The particles of all bodies (says he) may be considered as subject to the action of two opposite powers, repulsion and attraction, between which they remain in equilibrio. So long as the attractive force remains stronger, the body must continue in a state of solidity; but if, on the contrary, heat has so far removed these particles from each other as to place them beyond the sphere of attraction, they lose the cohesion they before had with each other, and the body ceases to be solid.”

† We have no reason to suppose that fluidity is an essential property of any liquid substance whatever; but rather that solidity is the natural state of all bodies, for we are able to reduce most substances to a state of fluiditý by the combination of caloric. In general, bodies treated in this way expand in all their dimensions, and the attraction of aggregation is so much weakened thereby, that the particles of the body slide over each other, and are put in motion by the slightest impulse. This is the only distinguishing character of fluidity that we are acquainted with.

On the contrary, the greatest number of liquid substances take a solid form by reduction of temperature. Thus water congeals, and forms ice. Even the gases show this disposition. The oxy-muriatic acid gas becomes concrete, and crystallizes at a temperature near to that at which water congeals. All the gaseous substances, when they have lost their elasticity by forming some combination, are disposed to assume the solid state, if the temperature allows it. Ammoniacal gas and carbonic acid gas become solid as soon as they enter into combination; and hydrogen gas, the most subtle of the ponderable elastic fluids, forms, with oxygen gas, the water which becomes ice.Berthollet's Chymical Statics, vol. 1, 2.

liquids by heat*. A larger portion of the matter of heat would convert them into vapour.

What other name is given to liquids?

They are likewise called fluids: we call the air a fluidt.

Why is the air called a fluid?

Because it flows like a fluid‡, and light substances will swim

in it.

Fluidity is owing to the matter of heat being interposed between the particles of the fluid; which heat would dissipate all fluids onto the air, were it not for the pressure of the atmosphere, and the mutual attraction which subsists between those particles. Was it not for this atmospheric pressure, water would not be known in any other states than those of ice and vapour; for, as soon as ice had acquired caloric enough to give it fluidity, it would begin to boil, and would be dispersed into the regions of space. This may be proved by direct experiment, as will be shown in the following chapter. The constitution of the world in this respect exhibits a beautiful instance of the harmony of nature, and of the exquisite contrivance of its divine Author. On the other hand, could we totally abstract the matter of heat from any fluid, no doubt but that fluid would, by that mean, be changed to a solid; the lightest vapours being nothing more than solids combined with heat.

Not only fluids, but all those substances which are soft and ductile, owe these properties to the chymical combination of caloric. Metals owe their malleability and ductility to the same cause.

The following experiment will prove, that it is caloric which converts solids to fluid-Expose a pound of water and a pound of ice, both at 32o, in a room, the temperature of wh ch is above the freezing point. The water will arrive at the temperature of the room several hours before the ice is melted. The caloric, therefore, which has all the time been entering into the ice, but is not to be found in it by the thermometer, must have become chymically combined with it in order to give it fluidity. The caloric appears to be lost; its properties are merged in the fluid just as muriatic acid, by union with lime, loses all its characteristic properties(Henry.) See this further explained in the chapter on caloric.

Steam is an

† Atmospheric air is one of the permanently elastic fluids. elastic fluid, but atmospheric air in all states, and in all seasons, is permanently elastic. This elasticity arises from caloric being chymically combined with the solid substances of which it is composed. I say solid, because we have abundant evidence that oxygen and nitrogen are both capable of taking a solid form, and actually do, in many instances, exist in a state of solidity. Nitrogen is a component part of all animal substances, and exists in a solid state in all the ammoniacal salts Oxygen takes the same state when it combines with metals and other combustibles; and in the composition of the nitrous salts, they both take the same state of solidity. These facts surely evince that atmospheric air owes its fluidity to caloric.

One of the general laws discovered by Dr. Black, and which he laid down as a chymical axiom, was, that "whenever a body changes its state, it either combines with caloric, or separates from caloric." The great number of natural appearances which are explained by this general law, renders it important, and it ought to be remembered by all those who wish to make a progress in the science.

The air is also known to be a fluid, by the easy conveyance which it affords to sound.

What is the cause of bodies swimming in fluids?

All substances will swim in fluids which are lighter than the fluid they swim in*.

Is this universally the case?

Yes; this is an established law of nature +. Thus a cork swims upon water, while a stone sinks in it.

Have you a clear idea of the cause of these substances sinking and swimming in fluids?

The one sinks because it is heavier, the other swims because it is lighter, than the water.

What do you really mean when you say that a stone is heavier than

water?

In chymical laboratories a vacuum is often formed in the retorts and other glass vessels, which occasions frequent explosions, and sometimes dreadful accidents. These are produced by a torrent of atmospheric air rushing into these vessels. If the air did not possess the common properties of fluids, these effects could not take place. It is a property of fluids to press in all directions, upwards as well as downwards; so does atmospheric air. * This may be shewn to a child at the breakfast table, by placing a teacup upon a bason of water, and informing him that it swims there because it is specifically lighter than a body of water of its own bulk. Water may then be gradually poured from the tea-pot into the cup; and he may be directed to observe how the cup sinks in the bason as it becomes loaded with water, untill the united weights of the water and the cup are too great for the wate in the bason to support, and the whole sinks.

Here the pupil may be informed that it is on this principle that ships and other vessels are constructed, and that it is this property of fluids which enables us to visit foreign countries, and bring our vessels back laden with their productions. The wisdom and goodness of the Almighty in imparting this property to water, may be insisted upon with great advantage. An enumeration of some of the consequences which would have resulted from an opposite constitution of things, would furnish matter for many interesting conversations.

The weight of goods in a vessel is indicated by the depth to which the vessel sinks in the water. In canal boats this is shown by graduated brass plates affixed to the sides of them. An account of a curious method of ascertaining the tonnage of ships hydrostatically, may be seen in the first number of the Retrospect. It is founded on the different draught which a ship will have in salt and in fresh water, owing to the different specific gravity of the two fluids. That nautical men should be acquainted with this hydrostatical axiom, is certainly of importance; for, should a captain load his vessel with a full cargo at any sea port, his vessel would inevitably sink when brought into the Thames.

Some of the questions in this introductory chapter may perhaps be thought trifling and insignificant; but the reader is requested to consider nothing unimportant which can tend to lay a just and stable foundation for the superstructure of an interesting science. The generality of elementary writers presume too much when they suppose that what they omit is universally known. Many things which they consider to be of public notoriety are known perhaps to few who have not paid a particular attention to the subject. Hence many works which are called elementary, disappoint the expectation of the student, and are laid by with distaste, for want of the first rudiments of the science being detailed with minuteness and simplicity.