nt with the greatest attenity of laying the improveeader,

, and is cultivated by so ual progress is exceedingly

of perspicuity, arrange the Is; because I consider any as greatly preferable to no

a

1815.)

in the Physical Sciences. employing galvanism as an instrument of analysis, and the proba bility by means of it of decomposing many bodies which had

previously resisted all the efforts of chemical experiment.

In this dissertation the author showed that bodies which have a chemical affinity for each other are in different states of electricity the one being negative, and the other positive. Thus' when quicklime and oxalic 'acid are brought' in contact, and separated, the acid is found to he negative, and the lime positive. Hence the reason why oxygen and acids are attracted by the negative pole of the battery. They are charged positively; and it is a law in electricity that bodies in different states are attractel by each other. Hydrogen, alkalies, earths, and oxides, are in a positive state of excitement; therefore they are attracted to the negative pole of the battery. Sir H. Davy conceives, with Volta, that there is a peculiar state of electricity, cither positive or negative, which belongs to every body ; that bodies which have an affinity for each other are in different states, and that the degree of affinity is proportional to' the intensity of these different states : or, in other words, the more positive one body is, and the more negative another, the greater is the affinity between them. If we bring them into the same state, that is, render them both positive or both negative, they will no longer remain in combination, but will separate from each other. Hence the reason why common electricity and the galvanic battery decomposes bodies; and it is probable that by its means most bodies may be decomposed, because the affinity between all bodies must be definite, whereas the galvanic intensity may be increased at pleasure almost to any amount. According to this view of the subject, chemical affinity is the same power with the attraction which exists between bodies in different states of electrical excitement; and if any means can be fallen upon to measure this power, we shall at the same time have a measure of chemical affinity..

Such is an outline of the hypothesis of Sir Humphry Davy. Every one, I conceive, who has considered it with attention, must admit the great importance of it as a means of advancing our knowledge of the constituents of bodies, and be aware that it was in consequence of it that Sir H. Davy was led to attempt the decomposition of the alkalies and earths, and to obtain the splendid success with which these fortunate attempts were attended. He will recollect also the facts advanced in support of it by Volta and Mr. Brande, and the happy facility with which it enables us to explain many things that formerly appeared exceedingly obscure.

I am far from pretending to call in question the probability that this hypothesis may ultimately turn out accurate, and think it entitled to the closest attention of every chemist and electrician; but if it be correct, I conceive that the theory of electricity, which at present prevails, will not be able to stand its ground. If negative and positive electricity be qualities inherent in bodies, and continuing in them after they unite together, I cannot for my part conceive the one to consist in a deficiency of electric matter, and the

A 2

w in his celebrated lecture tricity, published in the os, and which gained the st important discovery in in every point of view, to

Sir Humphry Davy's ple t discoveries were more , but they were all derived, pointed out the means of

der Chemie,'i, 116. neralogi, i. 1.

other in an excess of it. Neither can I conceive with M. Dufay, the Abbe Haüy, and some other French electricians, that negative electricity consists in one fluid, and positive electricity in another, which have an attraction for each other, and neutralize each other when they come in contact. But I can conceive negative and positive electricity to be two attractions inherent in different bodies, which make them unite with each other, and keep them united. But if we adopt this view of the subject, we are not only embarrassed by the difficulty of explaining many electrical phenomena, but we lose the benefit of all the facts stated by Volta, and of most of those advanced by Sir H. Davy in favour of his hypothesis. I myself, therefore, though disposed to think favourably of the Davian hypothesis of chemical affinity, consider it as very far from being sufficiently established to constitute the basis of our researches and our arrangements.

This, however, has been done by Berzelius, who has bestowed much attention on it, and is certainly far better acquainted with the facts brought to light in support of it than I can pretend to be. His view of the subject does not differ much from that of Sir H. Davy; but the additions which he has made when we come to compare them with the present theory of electricity, or with any theory hitherto proposed, are sufficiently puzzling. According to him the acid or alkaline nature of a body depends upon the state of its electricity. If it be permanently negative, it is of an acid nature ;

if it be permanently positive, it is alkaline. But when he adds that a body may be positive with respect to one body, and negative with respect to another; though nothing is more easy than to reconcile this with the common doctrine of chemical affinity, it would be somewhat difficult to reconcile it with the theory of etectricity. I am far from saying that the thing is impossible; but in order to attempt an explanation of it with success, it would be necessary to make very sweeping changes in the electrical doctrines at present admitted.

Berzelius has given a table of the chemical substances in the order of the intensity of their electricities, beginning with the one attracted most strongly to the positive pole, or the most intensely negative substance; and terminating with the body which is attracted most strongly to the negative pole, and therefore is most intensely positive. The negative intensity diminishes as we proceed downwards in the table, and at last in the centre finally disappears. Then the positive intensity begins ; at first very weak, but it gradually increases as we go downwards, and becomes greatest at the lower end of the table. Hence the affinity of the two substances at the two extremes of the table is greatest of all; and as we advance to the middle of the table, that affinity gradually diminishes, and at last disappears. As I do not know the data from which Berzelius constructed his table, I have no means of judging of its accuracy; but I shall give the table in this place, as being well entitled to the attention of the chemical reader. It is doubtless

supporters and combustibles. Those of the one series, according to bim, do not combine with those of the other; except sulphur and phosphorus, which combine both with the metals and alkalies, and therefore constitute, as it were, the transition from the one series to the other. He endeavours to distribute the bodies in these series in a kind of arithmetical progression, beginning with the most com-, bustible bodies, as hydrogen, ammonia, potassium; and continuing to the least combustible, as platinum, rhodium, iridium. If we suppose the series continued farther, we are led to the idea of a body absolutely incombustible. This body must possess in the highest degree the properties which are the opposite to combustibility, and in consequence of the attraction which exists between it and combustible bodies, it must produce the strongest action, which is that of combustion. This incombustible body, in the present state of our knowledge, is oxygen.

Between oxygen and iridium the author places carbon, phosphorus, and sulphur. This last substance, though heat makes it pass into the state of a combustible, ought to be considered as a negative body.

The products constitute a similar series, which commences with the most energetic alkalies, and passes to those which are more feeble, till we come to bodies such as alumina, in which that property is balanced by the opposite property having the same force. Then come bodies of a predominating acidity. This is at first feeble in the bodies nearest the point of equilibrium, but it becomes of an extreme activity in the bodies at the greatest distance from that point. We see that each series commences with a certain sum of a property, which diminishes in arithmetical progression, and terminates by leaving the bodies possessed of the opposite property.

Two bodies which belong to the opposite extremes of a series combine with great force; but the energy of this action seems to change their state, since the product of the combination no longer belongs to the same order of affinities. The compounds of oxygen and a combustible body pass into the series of products, as likewise do tlrose of hydrogen and sulphur, of tellurium, and without doubt those of various other bodies. The compound of an acid and alkali no longer belongs to the series of products, but to that of the salts. On the other hand, compounds between bodies at no great distance from each other, as between two acids or two alkalies, do not go out of the series.

This law embraces all the bodies having the same preponderating forces; so, however, that these bodies cannot be confounded. It presente, says the author, under a simple expression this truth, that the same force may exist in a state so different that all its attraetion for the opposite force will not be sufficient to make it enter into combination. The two most different states are found in the supporters and the products. The third state is in the neutral salts; but they bar a close resemblance to those products that are placed near the point of equilibrium.,, Combustibility, then, is the pres

e one series, according to ther; except sulphur and

metals and alkalies, and con from the one series to e bodies in these series in sing with the most comotassium; and continuing hodium, iridium. If we e led to the idea of a body st possess in the highest Ete to combustibility, and ists between it and comgest action, which is that y, in the present state of

places carbon, phosphohough heat makes it pass e considered as a negative

ponderance of the positive force in a particular state, which M. Oersted calls the state of supporters, or of the first class of bodies. Alkalinity presents the same force, but in a different state, which he calls the state of products, or of the second class. We do not know the nature of this difference, but we know that it exists, and that the forces are in a state of greater liberty in the first class than in the second.

Combustion sometimes gives us alkaline products, sometimes acid, and sometimes neutral ones. The product, by combining with oxygen, loses either in part or entirely its free positive force, and passes to the order of bodies of the second state. The same thing happens to the negative force of the oxygen. If the body be combustible in high degree, and does not combine with too much oxygen, the positive force still preserves the preponderance, and the body is alkaline. If, on the contrary, the body be but little combustible, and combine with a great deal of oxygen, the negative force remains preponderant, and the body is acid.

In oxygenated bodies we find of necessity a combustible body and oxygen united together, and constituting a body of the second class. Hence we must conclude that these bodies unité together the two opposite properties, the alkaline and acid, one of which is often rendered insensible by the other. However, in a great number of other combinations, boch properties subsist together. This is the case in the oxides of lead, copper, &c. In some bodies we find the positive or negative force in both státes at the same time. Thus ammonia possesses both the positive force of the first class and that of the second; while the nitric and oxymuriatic acids possess the negative force both of the first and second class. This is the natural effect of a combination, either feeble or far from the point of saturation, by which à force is reduced to an inferior state. In the combination of tellurium with hydrogen, the negative force of the metal is sufficiently changed by the positive force of the hydrogen to occasion a state of acidity. The positive force contained either in the hydrogen or in the tellurium bas not suffered enough of change to come to the state of acid. Hence we find in tellureted hydrogen gas a strong combustibility, and a very distinct acidity, existing together.

It is well known that electricity produces heat. M. Oersted ascribes this effect to a union between the two opposite electric forces; and it is so much the more intense, the greater obstacles the transmission of the electricity meets with, provided that these obstacles may be overcome. The transmission of electricity consists in a series of attractions and repulsions, or in the undulatory movement experienced by the peculiar forces of the body. Chemical union between electro-negative and electro-positive bodies excites always heat, and none of the electrical forces escapes in a state of liberty. However, the increase of conducting power may counterbalance this effect, and even overcome it, and then cold is excited.

There exists three principal combinations between the electrical

which commences with

those which are more cuina, in which that prohaving the same force. ty. This is at first feeble im, but it becomes of an atest distance from that s with a certain sum of a

progression, and termi: opposite property. site extremes of a series

of this action seems to e combination no longer le compounds of oxygen of products, as likewise ium, and without doubt ipound of an acid and ducts, but to that of the veen bodies at no great cids or two alkalies, do

a

he same preponderating not be confounded. It pression this truth, that ut that all its attraction to make it enter into ; are found in the supis in the neutral salts; roducts that are placed lity, then, is the pre