considered himself as entitled, by the results which he has obtained, to establish two propositions which he considers as axioms or chemical first principles, and which have a prodigious influence on the whole doctrine. These axioms are the following:

1. In all compounds of inorganic matter one of the constituents is always in the state of a single atom. According to this axiom, no inorganic compound is ever composed of two atoms of a united with three atoms of b, or of three atoms of a united with four atoms of b, &c.; but always of one atom of a united with one, two, three, four, &c. atoms of b. This axiom, if it hold good, which Berzelius thinks it will, greatly simplifies the doctrine of atomic combination, as far as inorganic bodies are concerned, and reduces the whole to a state of elementary facility.

2. When an acid unites to a base, the oxygen in the acid is always a multiple of the oxygen in the base by a whole number, and generally by the number denoting the atoms of oxygen in the acid. Thus sulphuric acid contains three atoms of oxygen: 100 parts of it contain 60 oxygen; and 100 parts of sulphuric acid combine with, and saturate, a quantity of base which contains 20 oxygen. Now 20 multiplied by three, the number of atoms of oxygen in sulphuric acid, makes 60 the quantity of oxygen in 100 of sulphuric acid.

Such are the two axioms of Berzelius, which he has made the foundation of his whole reasoning, and from which he has deduced his rules for determining the proportion of oxygen in bodies, and the number of atoms of which they are composed. If they hold good, and hitherto they have answered wonderfully well, they must be admitted to be of the utmost importance, and to give a facility and elegance to our chemical investigations which could scarcely have been looked for.

Mr. Dalton, the founder of the atomic theory, has not adopted either of these axioms. At the same time he has not advanced any fact in opposition to them; but only that there is nothing in the atomic theory which necessarily leads to their adoption. This is doubtless true. The axioms are merely empyrical, and deductions from analyses. Yet if they hold in all the analyses hitherto made, we cannot well refuse them a good deal of generality; and the best mode of proceeding seems to be to admit them till some exception to them be discovered.

Berzelius, considering the atomic theory to labour under difficulties, which in the present state of our knowledge we are not able to surmount, has substituted in its place another, which he conceives to be easier and simpler. This may be called the theory of volumes. He conceives bodies to be all in the gaseous state, and embraces the opinion of Gay-Lussac, that gaseous bodies always unite in volumes that are aliquot parts of each other. One volume of one body always unites with one, two, three, &c. volumes of another. How this alteration, which consists merely in the substitution of the word volume for atom, simplifies the atomic theory, or

removes any of the difficulties under which it labours, is, I own, beyond my comprehension. But Berzelius has deserved so well of chemistry, that he may be indulged in any innocent whim which produces no deterioration.

I should take up too much room were I here to give a table of the weights of the atoms of bodies. I must satisfy myself with referring to the different papers which I have inserted in the Annals of Philosophy on the subject, to the paper of Berzelius in the third volume of the Annals, in which will be found his table of the weights of an atom of the simple substances, and to Dr. Wollaston's scale of chemical equivalents. The weights given in these three different tables do not always coincide with each other; but in general a very near approach to coincidence will be perceived. In some cases the weights that I have assigned are half those given by Berzelius. The reason of this is obvious; and the circumstance can occasion no difficulty or ambiguity.

II. Light and Heat.

In the account of the progress of chemistry which I gave at the beginning of last year, I had to state a considerable number of important additions to the doctrine of heat, and its connection with light; but at present this department of the science is nearly barren. M. Berard has repeated and confirmed the experiments of Dr. Herschel on the heating power of the different rays of solar light. He found the greatest heating power at the extremity of the red ray. He likewise repeated the experiments of Wollaston, Ritter, and Böckman, on the deoxidizing power of the solar rays. He found it greatest, as they had done, in the violet ray; and traced it in a diminishing rate to the middle of the spectrum, where it disappeared.

Morichini, a Roman chemist, announced some time ago that, when steel needles are exposed to the action of the violet ray, they are converted into magnets. This experiment has been repeated in France, but has not been attended with success.

III. Simple Supporters and Combustibles with their Compounds. There are a considerable number of facts to relate respecting this branch of chemistry.

1. Iodine. This singular substance was discovered some years ago by M. Courtois, a saltpetre manufacturer in Paris. It was first examined by Clement and Desormes, then by Sir H. Davy, and lastly by Gay-Lussac. It is obtained from kelp by a very easy process, which has been described in the Annals of Philosophy. French kelp yields it in much greater abundance than British kelp. Hence it would appear that the sea plants that yield it are more abundant in the English Channel than on the east or west coast of Britain. Iodine is in small crystals, which Dr. Wollaston has ascertained to be octahedrons. It has the metallic lustre, and resembles plumbago in colour, though its lustre is considerably

greater. It has a peculiar smell, is very volatile, and very poisonous in its nature when taken internally. Its specific gravity is rather less than four, that of water being one.

Iodine, as far as experiment has hitherto gone, must be considered as a simple substance; and it belongs to the class of supporters, though it is by far the worst supporter known. Its vapour supports the combustion of potassium, and it combines rapidly with phosphorus, evolving much heat, though no light. When iodine is heated, it is volatilized at rather a low temperature, and converted into a beautiful violet-coloured vapour, from which it has received its name. This vapour, as far as I can find, possesses very little elasticity at the temperature of 212°.

Iodine combines with chlorine, and forms a peculiar acid. It does not appear to combine with oxygen. With hydrogen it unites, and forms an acid very much resembling muriatic acid in its smell, though I consider it as rather more pungent than that of muriatic acid. It unites with sulphur, phosphorus, and the metals; and forms a class of bodies, analogous to the oxides, called iodes. Some of these possess the properties of acids. It combines with alkalies and earths, and forms with them two classes of salts. The first, consisting of iodine and the base, may be considered as analogous to the iodes; the second, consisting of iodine, oxygen, and the base, have been called oxiodes, and may be considered as analogous to the hyper-oxymuriates. It scarcely possesses the property of separating carbonic acid from the bases, and cannot therefore be united with the carbonates so as to form salts; though these bodies readily dissolve a portion of iodine. An atom of iodine weighs about

12.5.

2. Chlorine.-Chlorine has the property of combining with two different proportions of oxygen, and of forming two new acids, which have received the names of chloric and chlorous acids. The first was discovered by Gay-Lussac; the second, by Sir H. Davy. The Germans have given to chlorine the name of halogen.

It is scarcely worth while to notice the experiments of the Dutch chemists L. A. Von Meerten and S. Stratingh on this gas, as I do not perceive any thing new in them. Meerten says that chlorine has the property of converting sulphurous acid into sulphuric acid, and nitrous gas into nitric acid. These were the first two experiments that I tried; when Davy published his paper to show that chlorine is still an undecomposed substance; and I soon procured the fullest evidence that neither of these gases is altered by pure chlorine; but when chlorine contains a mixture of common air, which it usually does, it renders nitrous gas yellow in an instant. Meerten found likewise that ether burns in chlorine gas. This discovery was made many years ago by Cruickshank, and published by him in the last volume of Nicholson's quarto Journal, and by myself in the second and subsequent editions of my System of Chemistry; nor is there any thing new with respect to the burning of the metals in chlorine gas, as far as tried by these chemists.

Christian Frederick Bucholz made a set of experiments, in 1812, to determine the quantity of oxygen which can be obtained from hyper-oxymuriate of potash. His experiments were not attended with much success; but he ascertained that a red heat is necessary to drive off this gas. I have myself repeated this experiment more than once, and obtained a result which approached very near to that previously established by the experiments of Chenevix.

3. Fluorine-Sir H. Davy has published several papers upon this hypothetical basis of fluoric acid; but all attempts to obtain it in a separate state have hitherto failed. Indeed, supposing it to exist, its action upon all other bodies seems necessarily to be so violent that there can be little hopes entertained of ever procuring it except in a state of combination.

4. Azote. The two laws of Berzelius relative to chemical proportions do not hold when applied to the combination of azote with oxygen. The reason of this he conceives to be, that azote is not an element, but a compound of oxygen and an unknown base, to which he has given the name of nitricum. He has calculated from his theory the quantity of oxygen which azote must contain; and he shows that when this correction is made, the nitrates, as well as other bodies, come under the dominion of his two laws.

Mr. Miers, of London, had been of opinion for several years that azote is a compound of oxygen and hydrogen, and that the experiments of Girtanner were not so inaccurate as has been supposed. In a paper published in the Annals of Philosophy, vol. iii. p. 364, he shows that the supposition, that it is a compound of one atom oxygen and six atoms hydrogen, will tally exactly with the atomic theory, and give the weight of the different atoms into which. azote entered the very same as they are at present, supposing azote to be a simple substance. This ingenious paper was sufficient to show us that the opinion of Mr. Miers was neither impossible nor improbable. It was not, however, sufficient to determine the opinions of chemists in favour of an hypothesis of so much importance, that the consequence of admitting it would be an almost entire change in the notions at present entertained respecting chemical combination.

Mr. Miers, sensible of the necessity of direct experimental proof in order to give currency to an opinion of such magnitude, has had recourse to direct experiment, and has published a very curious and valuable paper on the subject in the Annals of Philosophy, vol. iv. p. 180 and 260. His object in these experiments was to deprive water of a portion, but not the whole, of its oxygen, and thus to convert it into azote. The experiments of Girtanner were directed to precisely the same view. It occurred to Mr. Miers that sulphureted hydrogen gas would probably answer the purpose. Accordingly he passed a mixture of vapour of water and sulphureted hydrogen gas through a copper tube. In one experiment the whole gas that came over possessed the properties of common air, and was a mixture of 80 azote and 20 oxygen. In another a gas was formed, which Mr. Miers considered as sulphureted azotic gas. In a third

there was formed an acid gas resembling sulphureted hydrogen in smell, but possessing very different properties. Water absorbed twice its bulk of it. With potash it formed a black insoluble compound, not decomposed by any acid. Such were the different results obtained by Mr. Miers. They are highly curious and interesting; but it is obvious that they require to be followed farther before they can be considered as establishing the compound nature of azote, and that it is composed of oxygen and hydrogen. The inconsistency of the results with each other, the new facts brought to view by every repetition of them; and, above all, the circumstance of the gas, in the most decisive of all the experiments, possessing the properties and composition of atmospherical air, lead to suspicions which require to be obviated. It would be requisite, likewise, to account for the sulphur of the sulphureted hydrogen, and to show that the copper tube can have no influence on the decomposition of this gas. I hope, therefore, Mr. Miers will resume his experiments, and prosecute them till he obtains results free from all such anomalies, and leading to conclusions that cannot be controverted. The investigation is indisputably an object of importance; and he has made such progress in it, that he ought to enjoy the reputation that would infallibly result from so interesting a discovery.

5. Phosphorus.-The facts respecting phosphorus, published by Thenard in the Annales de Chimie, had been almost all anticipated long ago by Proust. Hence I conceive it to be unnecessary to detail them here. Heinrich, in his treatise on the phosphorescence of bodies, has stated some facts respecting the temperature at which phosphorus burns in various circumstances, which perhaps may be worth transcribing. When phosphorus is put into the bottom of a narrow glass tube, it may be heated to 482° without taking fire. In the open air phosphorus burns at 99°, and in oxygen gas at 72°. I cannot avoid observing that these determinations are far from precise. Indeed, nothing definite can be established respecting the combustion of phosphorus, because the degree at which it catches fire depends upon its purity. Pretty pure phosphorus I found did not begin to burn rapidly till heated to the temperature of 148°; but if you keep it long in the temperature of 990, its temperature gradually increases by its slow combustion, and it will, after a cer¬ tain time, burn rapidly. According to Heinrich, a compound of equal parts phosphorus and sulphur becomes luminous at 30°.

6. Ammonia.-The important experiment of Berzelius, who converted mercury into an amalgam, by causing the galvanic battery to act upon it when in contact with ammonia, has not yet been cleared up in a satisfactory manner. It follows from it that am- monia contains a substance of a metallic nature as its base, and that when this base is deprived of oxygen by the influence of the galvanic battery the metal amalgamates with mercury. On the other hand, the analysis of ammonia by means of electricity, and the resolution of it into hydrogen and azote without the least trace of