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A note gives a fuller account of Dr. Cullen's views; it was written in the year 1759. Elective attractions were in reality definitely laid down and presupposed in Geoffroy's tables ; but the investigation and elaboration was needed.* sent we must consider Dr. Cullen as the first who used the words and explanations in the manner afterwards made so famous by Bergman.
* Note E., p. 45., Cullen's Life, by Thomson, p. 570. Appendix. - The following passages from a letter, written by Dr. Cullen to his friend and former pupil, Dr. George Fordyce, of London, in October, 1759, contains his own statement of his views with regard to double elective attractions. “I must give you the manner of considering the subject, which I fell upon last session, and shall continue to employ as the most easy and simple. I begin with your third and fourth cases, and to these one general rule applies, viz., that when two mixts (compounds) are applied to each other, if in each mixt there is a substance, that from the table of elective attractions, is by itself capable of decomposing the other mixt, the attractions between these substances and the substances they attract in the opposite mixt, must always be greater than the attractions subsisting in the mixts applied to each other; and therefore, &c. Thus, if nitrum argenti and common salt are applied to each other, as by the table of elective attractions, the nitric acid in nitrum argenti, is by itself capable of decomposing the other mixt, common salt; and the muriatic acid in common salt is capable of decomposing nitrum argenti: the attractions between the nitric acid and the soda, with the attraction of the muriatic acid and the silver must be always greater than the attractions subsisting in the mixts, nitrum argenti and common salt, that were applied to each other. This I illustrate by the diagram adjoined. Let there be two rods intersecting one another, and moveable on a common axis at the point of intersection. At the extremities of each let there be placed substances that have an attraction for each of the substances on the extremities contiguous to them, and let the attractions be expressed by the letters W, X, Y, Z. The rest of the illustration will readily appear from the diagrams.
Ergo Y + 2 7 X - W You see that the prevailing attractions are here determined from the table of single elective attractions.
We are now come to the only difficulty in the affair of double elective attractions in instance past. To this our general rule does not apply.
There is no doubt that, however these opinions might be at the time floating amongst chemists, the works of Bergman were both the fullest and the most important on this subject. From them I shall give rather long quotations.
“On the different amount of phlogiston in metals, he says; calces (oxides) do not displace each other, as experience shows, at least, not in the same order as the metals do. May not therefore the quantity of reducing phlogiston in any metal be determined by a comparison of the weights of the precipitated and the precipitating metal? The following experiments will show the answer, but let us first examine, in a general way, those cases which may possibly occur :
“ Let A be the precipitating metal, m the weight of acid necessary for dissolving 100 of A, x the quantity of reducing phlogiston in 100 of A; B the metal to be precipitated, nm the weight of the solvent mentioned necessary for dissolving 100 B, and y the amount of reducing phlogiston in 100 B. n may be equal to unity, or it may be more or less than unity.”
“ Let, I., n = 1 then m = nm.”
(In other words, if n = 1 the quantity of acid necessary for dissolving the precipitating metal, it will be equal to the quantity necessary for dissolving the precipitated metal.)
“ In this case, if x=y there is no difficulty, because the solvent of each dissolves an equal weight, and B is able to take from A as much of the inflammable material as is necessary for its reduction.
See how it comes out when my new scheme is applied to it. Y and Z are by the table of elective attractions each of them less Vitriolic
Acid. than W, but greater than X. If, therefore, Y and Z are exactly as much greater than X, as they are less than W, the four attractions would be exactly
Nitric balanced; but if Y and Z exceed in any degree more Silver. X Acid. than they fall short of W, than Y + Z must be greater than W + X.
* Torberni Bergman, Opuscula Physica et Chemica, pleraque ante seorsim edita, jam ab auctore collecta, revisa et aucta. Holmiae, Upsaliae Aboae, &c. Vol. I., 1779, II., 1780, III., 1786, IV., 1787, V., 1758, VI., 1790.
+ Vol. III., p. 156.
“ If x is greater than y there appears still no obstacle to prevent complete precipitation.
“ But if x is less than y, so that only a part of B can be displaced, a portion of the dissolved precipitant must be sensibly thrown down, so as to act anew, or some other assistance must be given.
66 II. Let n 71 et m nm
“ With respect to phlogiston, this is the same result as in case I., but the obstacles are less.”
(That is, if the acid for dissolving the precipitating metal is less than the acid which dissolves the metal to be precipitated, as in this case, the precipitating metal would not cease its action for want of acid.)
III.) Let n < I then is m 7 nm. In this case B cannot be entirely thrown down, unless nx = y or nx 7 y, because only n 100 of the precipitant A is dissolved.”
(That is, if it requires more acid to dissolve the precipitating metal than the one in solution, then the metal in solution cannot be quite thrown down, unless it should be 'found that the amount of phlogiston in the precipitant is equal to the amount in the precipitate, or greater than it.)
Then, after recounting experiments, the first of which are made with a nitric acid solution, he says, p. 139 ;
“ Therefore 135 parts of mercury have reduced completely into the metallic form by means of their phlogiston, 100 parts of silver which had been dissolved and calcined. This had united with four times its weight of mercury, and crystallized in an arborescent form.
“ The amount of lead necessary for precipitating 100 lbs. of dissolved silver, amounts to 234 lbs.
“ C. 375 lbs. of shining plates of copper were put into a solution of silver, and were soon covered with a crystalline silver coating. When all the silver had fallen, the copper plates, when well cleaned, were found to have lost 31 lbs. The precipitated silver was found to amount to a cwt. (100 lbs.)
“ In order to examine into the power of different solvents, we precipitated with copper a hundredweight of silver, which was dissolved in vitriolic acid, but there were only 30 lbs. of
This, then, enables us, to some extent, to measure the great avidity with which nitric acid seizes on phlogiston, so much excelling the vitriolic acid.”
The amount of each metal needed to precipitate 100 lbs. of silver, is given with the experiments, but to save room, I add
Amounts of zinc used to precipitate 100 lbs. of metals. 217 lbs. Zinc precipitated.....
100 lbs. of pure Gold. 416
ditto Bismuth. 70 (the solution was difficult)
ditto Antimony. Scarcely any precipitation appears with Iron.” Then, at p. 150, there are certain corollaries, of which the following sentences suit best the subject in hand :
COROLLARIES. “ A. That dephlogisticated metals unite with different acids in a variable manner (i. e., that different amounts of metal unite to different acids). Thus, 100 parts of silver, dissolved in
nitric acid, are reduced by 31 of copper, but if united to vitriolic acid, they want only 30 of copper. In the same way 100 parts of copper, in a vitriolic solution, are restored to a metallic form by 146 pounds of zinc, but in a nitric acid solution, 164 lbs. of zinc are wanted. Therefore nitric acid dephlogisticates the metals most, vitriolic acid less, and muriatic acid still less.
“ B. Since we added the solutions in a saturated state, it is clear that the mutual quantities of phlogiston in the precipitate and the precipitant are in inverse proportion to the weights. Let the quantity of the phlogiston in a hundredweight of silver be 100, and the amount in a hundredweight of mercury will be 74, in lead 43, in copper 323, in iron 342, in tin 114, in bismuth 57, in nickel 156, in arsenic 109, in cobalt 270, in zinc 182, in antimony 120, in manganese 196.
“ D. Let us see then how those principles before-mentioned may be applied. With respect to silver, which answers to B, there is no precipitant or A, which acts so as to make n= 1. If mercury or lead is used, then n 7 1, but if copper, iron, tin, bismuth, nickel, arsenic, cobalt, zinc, antimony, or manganese is used, the case is n < 1. In the zinc precipitates n = 1 is also wanting. Gold, platinum, iron, and antimony, make n 7 1, all the rest n <l.
“ Page 155. According to the experiments produced, the metals richest in phlogiston, are platina, then gold, iron, copper, cobalt, manganese, zinc, nickel, antimony, tin, arsenic, silver, mercury, bismuth, and lead, so that, in some order, it approaches nearer to the first metal. The relative numbers designating the amount found in each, are to be sought by other methods. A trial of each of the metals, so as to obtain the attractions sought for, would be a great labour, if done with sufficient care and sufficiently repeated, but if the work were divided it would be easier. If one would choose for examination mercury, another lead, a third copper, and so on, so as to see their relation with respect to the others, then we