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CHAPTER VII.

PHLOGISTON PERIOD AND PROGRESS OF THE BALANCE.

In the 17th century innovations were beginning in chemistry, as we have already seen, but as usual, these did not all take one direction. Van Helmont put his little archaeus, a kind of intelligent agent, but with less independence than that of Paracelsus, into the stomach, to do the work which he could find no way of accomplishing by merely physical means. Thus things began a new mystical direction. Becher, in the Physicae Subterraneae, ridicules his archaeus and chimeras, and the whole host of “impudent chemists" also, who assert that they obtain salt, sulphur, and mercury, from all bodies, even animals and vegetables. He does not hesitate to call these the greatest falsehoods. He calls “elements the genuine and true things of which bodies consist, and from which others are made and prepared." * But as he held on by the four elements, we are not able to find in him much material.

He had the merit of raising inquiry in a high degree, and of bringing forward his great admirer, Stahl, who introduced phlogiston. In this chapter we have a class of men who have made another advance in experimenting, and whose works are the first which living chemists can, without difficulty, peruse. The advent of oxygen into science was preceded by a century of vague prophesyings. The use of the balance was becoming general, but men had no idea of the accuracy with which nature weighed, although they had long used the proper principle of making the earth the arbiter, by trying which side of the scale she drew most willingly towards her. They

Phys. Sub. Lib. i., sect. iii., cap. i., No. 12.

had no idea of the fineness of her touch, and her absolute refusal to make any allowance for inaccuracy in the construction of instruments. It was not even known that all bodies could be compared by their weights; why should they not as well be known by their lightness ? This plan had its fair trial. By a curious circle of reasoning, it was decided, that what we call oxygen, which makes an oxide, or calx of a metal, was sulphur; afterwards it was the principle of combustion ; not such an erroneous idea. Now oxides or earths were, of course, simple bodies; when they were reduced to metals in the fire, they combined with phlogiston; they became lighter. Therefore phlogiston had the principle of lightness in it. The rule generally is, that we should begin wrong. We now say the metal is simple, and by uniting with oxygen, it becomes a compound, and is heavier. As the metal burns and gives out heat, they said it gives out its phlogiston, and loses its principle of lightness.* Stahl calls it sulphur. This would scarcely come under our view had it not been the cause of so many inquiries in the same direction, as to bring about a result, derived from an analysis of all the oxides, and a careful comparison of the weight of the metals, with the weight of the oxides, whether produced by combustion or oxidation in the fire, or precipitated from their acid solutions. Even this strange theory tended in the right direction, although at first threatening to take a mystical course. We could scarcely have anticipated this difficulty of proving that all bodies have weight and not lightness, but our forefathers encountered it, and it may yet come to the struggle again, renewed in a higher form, when we have to deal with those physical existences, now called imponderables.

I am not aware that any one went into the subject with care before Bergman. He may be said to have introduced modern analysis. Before him analyses were not superior to

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p. 277. “ Traité de Soufre" Traduit de l'Allemand de Stahl. Paris, 1767.

those speculations about the constitution of bodies which in former chapters have been passed over.

I may indeed cite here Roger Bacon's syntheses of bodies from the four elements, as the earliest examples of an endeavour to shew how so many bodies can be formed from few elements, and on the other side, as the fullest example I know of early analysis, and perhaps the very first in which numbers are used in connection with elements. They are intellectual strivings after quantitative analysis.

“ There is, therefore, one different kind where fire and air are greater; 2ndly, where fire and air are less ; 3rd, where fire and water are greater; 4th, where fire and water are less; 5th, where fire and earth are greater; 6th, where fire and earth are less; 7th, where air and water are greater; 8th, where air and water are less; 9th, where air and earth are greater; 10th, where air and earth are less; 11th, where water and earth are greater; 12th, where water and earth are less; and so you have two diversities. Next you have three diversities; 1st, where fire, air, and water are greater; 2nd, where fire, air, and water are less ; 3rd, where air, water, and earth are greater; 4th, where fire, water, and earth are greater; 5th, where air, water, and earth are less; 6th, where fire, water, and earth are less; and in this manner, if you divide those methods, you obtain from the first 16, from the second 64, from the third 47, from the fourth 18, in all 145. I will now speak of the fourth diversity, fire much, air less, water much, earth less; second, air much, water less, earth less, fire less, and so being ingenious, you may draw out all these diversities to light.”

A manuscript copy of Dr. Cullen's lectures in 1762-3 in the laboratory of Owens College, Manchester, from the late Dr. Henry's library, mentions four elements, which, by simple combination, could be formed into seven, but any proportionate combination to account for the number in nature, is not given.

These lectures shew him to have been an exceedingly clear and rational expounder of science. With good common sense he waits for more knowledge when science fails, fully shewing why he became famous, although he published very little. Reasoning on the state of things at the time, he says, “ It appears, then, that we know of no physical element, nor any chemical principle, nor are we acquainted with any body which has fixed and permanent qualities.”

He afterwards adds, “Having laid down and demonstrated this fundamental proposition, viz., that the changes of the qualities of bodies are all of them produced by combination or separation, I now proceed to inform you that combination depends upon attraction, that is, the attraction of cohesion, whereby the small particles of bodies very near each other are disposed to approach, and in a certain contiguity to remain coherent together."

He then goes on to explain simple elective attraction and double elective attraction by diagrams, like those below, where the lines ought to be drawn straight from C to B, and from A to D. This appears to be earlier than Bergman, who at that time had published nothing on chemistry. I can find no internal evidence of their being written later than they profess to be, the binding itself being old.

Dr. Cullen was professor of chemistry at Glasgow, and Dr. Black attended his lectures, before being appointed his successor, on the removal of Dr. Cullen to Edinburgh, in 1756. In the Annals of Philosophy, Vol. III., p. 554, Dr. Thomson says:—“My knowledge of Dr. Cullen's opinions was derived from the late Professor Robison, of Edinburgh, who had the means of information, and, as he was a particular friend and great admirer of Black, is entitled to credit. Now, he informed me that Dr. Black's explanation of double decompositions, which he annually gave in his class, had been originally broached by Dr. Cullen. This was the circum

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stance that induced me to broach Dr. Cullen's name along with Black and Bergman.

As to Dr. Black, I consider myself as acquainted with his opinions, because I attended his lectures; and there are thousands in Great Britain who did the same, and who cannot but recollect the facts that I shall state. Dr. Black taught that bodies combine in definite proportions, and he explained double decomposition by means of diagrams, not, indeed, the same as those of Mr. Higgins, but much simpler and more elegant. I have been informed by Prof. Robison, that he employed these diagrams from the very beginning of his career, as a professor. One of them is given in page 554, Vol. I., of his printed lectures. I have no doubt that all similar diagrams, published in London, by Fordyce, &c., were derived from the same source. Now, could the doctrine of definite proportions be taught, and could double decomposition be explained in this way (I quote Dr. Black's explanation), let the bodies A and B be 10 united with a force, 10; and the bodies C and D with a force, 6. Suppose the attraction of A for C to be 8, and that of B for D to be 9, if we mix 6 these bodies, A will unite with C, and B with D. To me they conveyed just as much of the atomic theory as the perusal of Mr. Higgin's book did.”

Dr. Robison edited the lectures of Black in 1803, and in a note gives the above diagram and some judicious remarks, shewing, at the same time, that although definite proportion was taken for granted, no general law to account for it had been given.

But the question cannot be as to whether Dr. Cullen discovered the atomic theory, (indeed, this extract might have been brought on somewhat later), but whether Dr. Cullen had so far advanced our knowledge of matter as to be the first who gave out the ideas of single and double elective attractions, such as have been attributed to Bergman.

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