observed, to be another power in nature upon which the various forms of matter greatly depend. It is that power which occasions in us the sensation of heat, and is now called caloric.

While attraction of cohesion is always endeavouring to bring the particles of matter nearer to each other, caloric is endeavouring to separate them to a greater distance-hence result the various forms of solid, liquid, and gaseous bodies. When attraction of cohesion predominates, the substance acted upon is solid,when cohesion and calorific repulsion balance each other, the substance assumes a liquid state,-when calorific repulsion prevails, the substance becomes aëriform or gaseous. This is exemplified in the several states of ice, water, and steam.

Suppose the power of cohesion were suddenly withdrawn from the earth, leaving its antagonist, caloric, to exert its power uninfluenced, what would be the effect? The particles of matter of every kind, even of the hardest rocks, would separate from each other and be driven into the immensity of space, leaving no appearance of anything material. How easily by such an act might the Almighty destroy a world.

Mr. W. illustrated the nature of cohesion by a variety of experiments.

The next agent, observed Mr. W., is light-the influence of which upon the animal and vegetable kingdoms is particularly manifest. The infinite variety of colours in the vegetable kingdom, the delightful odours of flowers, and their delicious fruits, depend entirely upon the genial influence of the light and warmth of the sun. But even unorganized matter is in some degree under the influence of light, and many chemical phenomena are produced by its presence. The combination of chlorine and hydrogen gases, which constitute muriatic acid, does not take place without the presence of light. The crystallization of bodies is greatly influenced by light. Steel needles are rendered magnetic by the violet-coloured ray of light.

The last agent which it will be necessary to notice is electricity. The influence of this agent in the economy of nature is exceedingly important, and in many cases most surprising. Among the natural phenomena dependent upon electricity, we may enumerate the formation of clouds, of dew, rain, hail, and snow, and probably the aurora borealis. The vital principle of animals and of vegetables is considered by some physiologists as dependent upon electricity. The simplest mode of exciting the electricity of bodies is by friction, as was done in amber by the ancients. But it may also be made sensible to us by other means. By heating some crystalline bodies, as the tourmalin and boracite, they exhibit electrical phenomena; by the mere contact of two dissimilar metals, as was first shewn by Volta, and hence it has been called Voltaic electricity; and also by the mixture of bodies chemically. It is very probable, indeed, that what is called chemical attraction or affinity, is entirely dependent upon the electrical relations of bodies.

It has also been rendered highly probable by recent discoveries that magnetism is identical with electricity. Magnetic attraction may easily be communicated to a bar of iron by the influence of electricity. So extraordinary, indeed, is this influence, that a bar of iron about two feet long may be instantly rendered so powerfully magnetic as to support a weight of two or three hundred pounds, and by a combination of such bars a weight of more than two thousand pounds has been supported.

Mr. W. exhibited this experiment by a very simple but powerful apparatus. He then said, having briefly noticed the influence which attraction of gravitation, heat, light, and electricity, have in the various operations of nature, I shall proceed to consider more particularly what is called chemical attraction or affinity, upon which depends the immediate combination of the elementary bodies with each other.

Chemical affinity only takes place at insensible distances this may be shewn by putting carbonate of soda and tartaric acid in powder together. Although the particles of each appear to be in contact, yet no union takes place so long as they remain dry, but on the addition of water, which dissolves them, and brings their particles into closer contact, then chemical union is effected. Cohesive attraction must be overcome before chemical affinity can take place-this is sometimes effected by heat, as when copper and zinc are melted together to form brass. That one or both of the substances to be united should be in a liquid state, was formerly laid down as a chemical axiom, 66 Corpora non agunt nisi sint fluida ;" but to

this law there are some exceptions. Oxalic acid and lime unite in the dry state, and snow and salt will combine without being first melted.

That chemical affinity is dependent on the electrical states of bodies, has been rendered highly probable from the experiments of Sir H. Davy and others. Substances that have ordinarily powerful affinities for each other may be separated by the electric agency, and one body may be made to pass through another for which it has commonly a strong affinity, without combining it-thus acids will pass through alkaline solutions, and alkalis through acids, without combination.

A knowledge of chemical affinities enables us to separate substances from each other, and to unite others, so as to form new compounds.

When one substance is employed to separate another from its combination, it is effected by what is called single elective affinity, as when sulphuric acid is added to a solution of muriate of baryta-the baryta leaves the muriatic acid, combines with the sulphuric acid, and is precipitated as the insoluble sulphate of baryta.

When one compound, containing two substances, is employed to decompose another compound, and two new compounds result from the decomposition, the exchange is effected by what is termed double elective affinity: thus, when a solution of carbonate of potash, and a solution of sulphate of magnesia are mixed together, the carbonic acid leaves the potash to combine with the magnesia, and form the insoluble carbonate of magnesia which is precipitated-while the sulphuric acid leaves the magnesia to combine with the potash, forming sulphate of potash. Bergman, who introduced these terms, conceived that chemical action was, in all cases, owing to elective affinity, and, accordingly, he drew up tables of affinity between different bodies; but Berthollet pointed ont the error of Bergman's opinions, and shewed that chemical affinity is not invariably the same in all cases. He attempted to prove, indeed, that it is always influenced by modifying circumstances, such as temperature, cohesion, elasticity, and quantity of matter. But in this attempt Berthollet went rather too far. That chemical affinity is greatly influenced by them is true-but still chemical affinity exists independent of them. Thus when iron, lead, and silver are exposed to the action of oxygen or atmospheric air, the iron readily unites with the oxygen, the lead gradually combines with it, but the silver is scarcely affected by it; and under the same circumstances we find water much more disposed to combine with some substances than with others; with muriatic acid gas it combines much more freely than with carbonic acid gas, and with the latter gas still more freely than with oxygen. Oil has no disposition to combine with water, yet it readily unites with a solution of potash forming soap.

The effect of one of the modifying circumstances of Berthollet may be seen in the following experiment :-On passing a stream of hydrogen gas over the oxide of iron heated to redness, the oxygen of the iron will unite with the hydrogen, and form water; again, on passing the vapour of water over iron filings, heated to redness, the iron will separate the oxygen from the vapour of water. From the first experiment it follows that hydrogen has a stronger affinity for oxygen than iron has; but from the second, it would appear that iron has the strongest affinity for oxygen, because it separates that element from its combination with hydrogen. This alteration of affinities between hydrogen, oxygen, and iron, is probably owing to an alteration in their electrical conditions effected by the agency of caloric. The effect of heat and elasticity in modifying chemical affinity, is exhibited very clearly in the formation of carbonate of ammonia by sublimation, from muriate of ammonia and carbonate of lime. If a solution of carbonate of ammonia and muriate of lime be put together, a double decomposition will follow. The carbonic acid will leave the ammonia to unite with the lime, forming an insoluble precipitate of carbonate of lime, while the muriatic acid will leave the lime to combine with the ammonia, forming muriate of ammonia. From what takes place in this experiment it would scarcely be expected that carbonate of lime could be made to decompose muriate of ammonia; yet by putting these substances together and applying heat, a decomposition is effected, and the muriatic acid again combines with the lime, forming muriate of lime, while the carbonic acid leaves the lime, and again unites with the ammonia, forming carbonate of ammonia.

When bodies unite with each other, the resulting compounds always possess properties differing from those of their constituents. Thus, highly corrosive and pungent bodies often become tasteless and inodorous; and, on the other hand, tasteless and inodorous bodies become corrosive and pungent. Solids become

liquids, and liquids and gaseous bodies often become solid. Gypsum, or plaster of Paris, a perfectly tasteless substance, is composed of 40 parts of sulphuric acid, and 28 parts of quick lime, both highly corrosive bodies. Common salt is composed of 36 parts of chlorine, a very suffocating gas, and 24 parts of sodium; the metallic base of soda. The salt called salam moniac, is composed of two gases, viz., the muriatic acid gas and ammoniacal gas.

Mr. W. here illustrated the above remarks by numerous interesting experiments; among which were the following:

1. On mixing together sulphuric acid, and a solution of pure potash, both corrosive bodies, they formed a neutral solution of sulphate of potash, possessing a slightly saline taste, but neither acid nor alkaline.

2. On introducing ammoniacal gas and carbonic acid gas into a glass vessel, they combined and formed a crystalline solid. Carbonate of ammonia.

3. On mixing together solutions of muriate of lime and carbonate of potash, the two liquids instantly became solid.

4. On displaying about four ounces each of salammoniac, salt petre, and glauber's salt in about a pint of water, and introducing a glass of water into the solution, the water in the glass was speedily frozen, and a degree of cold produced as low as 20° below the freezing point.

5. On mixing sulphuric acid and water together, a temperature equal to that of boiling water was instantly obtained, and spirits of wine, contained in a long glass, boiled in it. Mr. W. then adverted to the proportions in which bodies unite in the formation of compounds.

Bodies appear to unite together in three ways. First, unlimitedly in every proportion, as when spirits of wine and water, or sulphuric acid and water, are mixed together; a drop of sulphuric acid may be combined with a gallon of water, or a gallon of water may be combined with a drop of sulphuric acid, and the two substances will be found intimately united in every portion of the liquid.

Secondly, in every proportion within a certain limit, as when salts are dissolved in water; thus 100 pounds of water will dissolve any quantity of salt not exceeding 40 pounds. These kinds of combinations, however, may be regarded rather as mixtures than as chemical compounds; these substances undergo no particular change by their union, and they still possess the separate properties of each of the components.

The third kind of combination always takes place between bodies in limited and definite proportions, the knowledge of which constitutes an exceedingly interesting and useful branch of study. The compounds thus formed always possess properties essentially different from their constituents.

In this way some bodies unite only in one proportion, as hydrogen with chlorine, forming muriatic acid; no other compound of these two elements being known. Other bodies unite in two proportions, as hydrogen with oxygen, forming water, and deutoxide of hydrogen; others unite in three, four, five, and, even, six proportions; but whenever two substances form more than one compound, the other compounds contain multiple proportions of one of the elements of the first compound; for instance, there are two compounds of mercury and oxygen, and they are thus constituted.

1st. 8 parts of Oxygen to 200 parts of Mercury.
2d.-16 parts of Oxygen to 200 parts of Mercury.

The first is called the protoxide, the second, the per-oxide, of mercury. Oxygen combines with nitrogen in no less than five distinct proportions, thus:

1.-Protoxide of Nitrogen,
2.-Deutoxide of Nitrogen,..

3.-Hyponitrous Acid,

4.-Nitrous Acid,

5.-Nitric Acid,

8 Oxygen, 14 Nitrogen.
16 Oxygen, 14 Nitrogen.
24 Oxygen, 14 Nitrogen.

32 Oxygen, 14 Nitrogen.
40 Oxygen, 14 Nitrogen.

It will be observed that each of the proportions of oxygen is a multiple of 8, while the proportion of nitrogen remains 14 in all the compounds. These numbers are the relative weights of each substance.

Occasionally, however, we meet with two compounds, the second of which contains only one-half more of one of the elements, for instance, the two oxides of iron and the three oxides of lead are thus formed:

If we consider the proportions in which bodies unite with each other, as representing the relative weights of their atoms, it would follow that the first oxide of iron is composed of one atom of metal to one of oxygen; and the second oxide, of one atom of metal to one and a half of oxygen, or, rather, (to avoid the absurdity of splitting an atom,) of two atoms of iron with three atoms of oxygen; and we may consider the three atoms of lead as similarly constituted. But it is not necessary to involve the question of the atomic theory, which is hypothetical, with the practical consideration of chemical equivalents. It has been ascertained, by direct experiment, that all bodies unite together chemically, in definite proportions, which are fixed and invariable; these proportions, when reduced to their smallest quantities, compared to some element as a standard, are called equivalent proportions, or combining proportions; thus taking hydrogen as unity, the following are the equivalent proportions of

The equivalent proportions of all the elementary bodies have been ascertained, as correctly as the present state of chemical science admits, and, although there is some difference in the estimations of different chemists, yet it seldom amounts to anything very considerable. (A table of the combining proportions of all the elementary bodies was exhibited in the lecture room.)

Whenever any of the elementary bodies unite together, they unite in equivalent proportions, or in multiples of those proportions; and even when two compounds unite together, the same order of definite and multiple proportions prevails; for example, there are two compounds of carbonic acid and potash; they are composed 1st.-Carbonic Acid, 22, Potash,.... 48 2nd.-Carbonic Acid, 44, Potash,.... 48

The second (bicarbonate of potash) contains twice as much carbonic acid as the first. In order to arrive at the equivalent proportions of carbonic acid and potash, it is necessary to refer to the equivalents of their elements, thus, carbonic acid is composed of one equivalent of carbon, 6, and two equivalents of oxygen, 16, making 22. Potash is composed of one equivalent of potassium, 40, and one of oxygen, 8, making its equivalent 48.

A knowledge of the laws of combination is of the greatest utility to the practical chemist. By knowing the equivalent or combining proportions, he can, with the greatest ease, tell the proportions of the elements which constitute any compound, the quantity of any substance necessary to decompose it, and the amount of the new products.

Mr. W. next proceeded to explain numerous applications of the laws of equivalent proportions, and pointed out their particular use to the manufacturer, as well as to the scientific chemist. He then concluded his lecture, which was evidently. received with great interest and satisfaction, by a most respectable audience.

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