A Dissertation of Elective Attractions

Torbern Bergman

• Publisher: Routledge
• Year: 2020
• eBook ISBN: 9781136956850
• Topic: History
• Subtopic: World History
• Index: History

First Published in 1970. This is the second edition of Dissertation of Elective Attractions, by Bergman, and includes a new introduction. The text was first published in English in 1785 after being translated from the original latin in 1775 by Thomas Beddoes. The text is an introduction to the table of elective attractions used in chemistry.

DISSERTATION, &c.
ON
ELECTIVE ATTRACTIONS.

Jamne vides igitur magni primordia rerum

Referre, in quali sint ordine quæque locata,

Et commista quibus dent motus accipiantque.

Lucretius.

This Dissertation was first printed in 1775, in the third volume of the New Upsal Transactions. It was afterwards translated both into German and French. The two annexed Tables, which exhibit the single and double attractions, were again engraved in London, by the care of Dr Saunders, for the use of those who attended the lectures which he read in conjunction with Dr Keir. The same year, Mr More, secretary to the Society for the Encouragement of Arts and Manufactures, published the table of elective attractions, on a large sheet, substituting English words in the place of the signs.

I.
There seems to be a Difference between Remote and Contiguous Attraction.

It is found by experience, that all substances in nature, when lest to them-selves, and placed at proper distances, have a mutual tendency to come into contact with one another. This tendency has been long distinguished by the name of attraction. I do not purpose in this place to inquire into the cause of these phænomena; but, in order that we may consider it as a determinate power, it will be useful to know the laws ta which it is subject in its operations, though the mode of agency be as yet unknown.

It has been shewn by Newton, that the great bodies of the universe exert this power directly as their masses, and inversely as the squares of their distances. But the tendency to union which is observed in all neighbouring bodies on the surface of the earth, and which may be called contiguous attraction, since it only affects small particles, and scarce reaches beyond contact, whereas remote attraction extends to the great masses of matter in the immensity of space, seems to be regulated by very different laws; it seems, I say, for the whole difference may perhaps depend on circumstances. Considering the vast distance, we may neglect the diameters, and look upon the heavenly bodies, in most cases, as gravitating points. But contiguous bodies are to be regarded in a very different light; for the figure and situation, not of the whole only, but of the parts, produce a great variation in the effects of attraction. Hence quantities, which in distant attractions might be neglected, modify the law of contiguous attraction in a considerable degree; and, moreover, the great power of our globe on all occasions influences and disturbs it. This force may therefore produce wonderful variations in the effects, according to circumstances. But as we are by no means able to ascertain the figure and position of the particles, it remains that we determine the mutual relations of bodies with respect to attraction in each particular case, by experiments properly conducted, and in Sufficient number.

As contiguous attraction Scarce extends beyond contact, it is obvious, that the former will be more intense in the same body, the more the latter is increased. Hence, in the following observations, many instances occur, which prove that a body has greater power in a liquid than in a solid state, and still greater when it is resolved into vapour. See, in particular, what is said of marine acid, with respect to phlogiston, in the forty-seventh paragraph; and of the matter of heat, in the forty-eighth.

In this differtation, I shall endeavour to determine the order of attractions according to their respective force; but a more accurate measure of each, which might be expressed in numbers, and which would throw great light on the whole of this doctrine, is as yet a desideratum^*.

* Mr Morveau, I believe, first determined and expressed in numbers the cohesion of quicksilver to some of the metals. Mr Achard afterwards published a large table,, in which the cohesive force of many bodies is investigated both by calculation and experiment, Mr Kirwan very lately began to measure the attractions, by the diminution of bulk that is produced by union; for he is of opinion, that the cause and quantity of contraction is to be sought in the force of attraction.

Several species of contiguous attraction may be distinguished. I shall here briefly mention the principal. When homogeneous bodies tend to union, an increase of mass only takes place, the nature of the body remaining still the same; and this effect is denominated the attraction of aggregation. But heterogeneous substances, when mixed together, and left to themselves to form combinations, are influenced by difference of quality rather than of quantity. This we call attraction of composition; and when, it is exerted in forming a mere union of two or more substances, it receives the name of attraction of solution or fusion, according as it is effected either in the moist or the dry way. When it takes place between three respectively, to the exclusion of one, it is said to be a single elective attraction; when between two compounds, each confiding of only two proximate principles, which are exchanged in consequence of mixture, it is intitled double attraction. I am particularly to consider the two lad species.

II.
Single Elective Attractions.

Suppose A to be a substance for which other heterogeneous substances a, b, c, &c. have an attraction; suppose, further, A, combined with c to saturation, (this union I shall call Ac), should, upon the addition of b, tend to unite with it to the exclusion of c, A is then said to attract b more strongly than c, or to have a stronger elective attraction for it; lastly, let the union of Ab, on the addition of a, be broken, let b be rejected, and a chosen in its place, it will follow, that a exceeds b in attractive power, and we shall have a series, a, b, c, in respect: of efficacy. What I here call attraction, others denominate affinity; I shall employ both terms promiscuously in the sequel, though the latter, being more metaphorical, would seem less proper in philosophy.

Geoffroy, in 1718, first exhibited at one view the series of elective attractions, by arranging in a table the chemical signs, according to a certain order; but this admirable contrivance, while it is commended by some, is blamed by others; one party contending, that affinities are governed by fixed laws, and the other affirming, that they are vague, and to be ascribed to circumstances alone.

Now, since all chemical operations consist either in analysis or synthesis, composition or decomposition, and both the one and the other depend on attraction, it will certainly be of great importance to determine this dispute. Let us not then lightly, and on account of one or two irregularities, perhaps ill understood, reject the whole doctrine, but let us rather proceed in our examination with caution and care. Should we even at lad find that attractions depend on circumstances, shall we therefore conclude, that it will be useless to know the several conditions that forward or impede or disturb them ? By no means, but rather that it will be of extensive utility. There does not exist in all nature a single phænomenon but what is so connected with certain conditions, that when they are absent, the phænomenon shall either not appear, or be varied occasionally. It is of consequence to science, that the changes and the combination of causes in every operation should be accurately known, as far as a knowledge of them is attainable; and the utility of a strict inquiry into attractions will, I hope, clearly appear from many instances in the following pages.

But if, on the contrary, a fixed order does really take place, will it not, when once ascertained by experience, serve as a key to unlock the innermost sanctuaries of nature, and to solve the moil difficult problems, whether analytical or synthetical ? I maintain, therefore, not only that the doctrine deserves to be cultivated, but that the whole of chemistry rests upon it, as upon a solid foundation, at least if we wish to have the science in a rational form, and that each circumstance of its operations should be clearly and justly explained. Let him who doubts of this consider the following observations without prejudice, and bring them to the test of experiment.

III.
Whether the Order of Attractions be constant.

This question can only be properly answered from what follows. But let us now slightly consider whether a constant series, such as is mentioned in the last paragraph, is to be expelled. Does a expel b, and b a reciprocally, according to circumstances ? Does c perchance expel a, while it always gives way to b ? Let us consult Experiment, the oracle of nature, with due care and patience, and we (hall doubtless find the proper clue to guide us out of this labyrinth.

I am far from approving of those general rules which affirm, that earths and metals are in all cases precipitated by alkalis, and metals by earths, for they are often fallacious. We have, however, many particular observations, which, when every thing is properly disposed, never mislead. We know, for instance, that volatile alkali is dislodged by fixed alkali and pure calcareous earth; that quicksilver and silver are precipitated from nitrous and vitriolic acids on the addition of copper, which is again separated by iron. Silver, quicksilver, and lead, which were called the white metals by the ancients, are separated from the nitrous acid both by the vitriolic and marine. Do not these, and other fads long since known, shew, that there prevails a constant order among these several substances ? Many other clear proofs occur in the explanation of the new table of attractions, which I shall reserve for their proper places, (XII.—LXX.). The difficulties, when closely examined, disappear; and none has yet, as far as I know, been pointed out which is really inconsistent with a continued series. But should here occur in this, as in other branches of natural philosophy, a few phænomena, which appear to deviate from the ordinary track, they should be considered as comets, of which the orbits cannot yet be determined, because they have not been sufficiently observed. Repeated observations, and proper experiments, will in time dispel the darkness.

That the effect: of three substances mixed together may appear at one view, I have contrived a way of representing it by symbols. It will be proper to illustrate it by an example.

Scheme 20. Pl. 1. exhibits the decomposition of calcareous hepar by the vitriolic acid. On the left fide appears the hepar, indicated by the signs of its proximate principles united; but within the vertical bracket these principles are seen separate, one above the other. On the right, opposite the calcareous earth, is placed the sign of vitriolic acid; in the middle stands the sign of water, intimating that the three surrounding bodies freely exercise their attractive powers in it. Now, as vitriolic acid attracts calcareous earth more forcibly than sulphur does, it destroys the composition of the hepar; the extruded sulphur being by itself insoluble falls to the bottom, which is signified by the point of the lower horizontal half-bracket being turned downwards; and as the new compound, vitriolated calcareous earth (gypsum), also subsides, unless the quantity of water be very large, the point of the upper bracket is likewise turned downwards. The complete horizontal bracket indicates a new combination, but the half-bracket serves merely to shew by its point whether the substance from which it is drawn remains in the liquor, or falls to the bottom. The absence of horizontal brackets indicates that the original compound remains entire. Such a combination only as continues unaltered can have a place on the right fide, for if it be likewise decomposed, a new case arises, which will be noticed hereafter, (V.). Those operations which are performed in the dry way, are distinguished by the character of fire, which is placed in the middle.

IV.
A Difference in the D...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Publisher’s Note to the 1970 Edition
• Introduction to the 1970 Edition
• Orginal Title Page
• Preface
• Contents
• A Dissertation on Elective Attractions
• Notes on the Preceding Dissertation
• Explanation of the Table of Double Elective Attractions
• Emendanda
• Appendix I: A Note on the Identity of the Translator
• Appendix II
• Index