Part 11
But now, to sum up the evidence, which these experiments, taken all together, do afford, concerning the mineral ingredients of this Spaw; I think they determine, with some degree of certainty, that it contains two different principles of iron, both of which are fixed. The one, which is the ochrous earth, is a true _minera ferri_, and, altho’ it be a crude mineral, exists in the water in a very fine and subtile form; the other, which is the cremor or pellicle, whose parts are also extremely attenuated in the water, appears to be iron, not in its mineral, but in its metalline form, and, when thrown up upon the surface of the water, shews itself like an extreme thin _lamina_ of that metal. There seems also to be some small proportion of sulphur joined with the metalline cremor. The other mineral ingredient, which enters into the composition of this Spaw, is a considerable proportion of an aluminous salt, which is conjoined with a small quantity of a light brown-coloured earth (probably a part of the matrix whence the salt is formed), and still more intimately connected with some of the chalybeat parts of the water, which are not separable from it either by elixation or evaporation. Whether these be saline or terrestrial, I cannot determine.
Having thus endeavoured to discover, by some plain and simple experiments, the mineral principles, with which this medicinal water is impregnated; I shall now only add some observations, with respect to the origin of steel waters, and particularly of this Spaw, whose origin, I think, is thereby discovered and ascertained in a very obvious manner.
Among several things, that are still deficient in the history of mineral waters; an exact knowlege of their origin seems to be the chief; that is, from what fossils, and in what manner, these waters do acquire the mineral substances, with which they are impregnated. As this happens in the bowels of the earth, and is therefore far removed from our view, it is not surprising, that there has been so little discovered concerning it; tho’ indeed there have been many elaborate hypotheses framed in order to account for it.
The writers on mineral waters have been of very different and opposite opinions concerning their origin. They have disagreed widely amongst themselves; and I very much suspect, that the accounts, which most of them give of this matter, are not agreeable to truth: particularly with respect to chalybeat waters, I have seen none, who have given a satisfactory account of their origin. They have all agreed, that iron, or the vitriol of that metal, does exist in mineral waters; but they have never yet agreed, how they came to exist in them, or in what manner mineral waters come to be imbued with these fossils.
Some of the more ancient writers cannot comprehend, how simple water should be intimately impregnated with so many different kinds of minerals, except by the means of some powerful agent. And as they thought nothing more proper for communicating and mixing mineral substances with water, than violent heat, they therefore termed all mineral waters, of whatever kind, by the name of _thermæ_. They saw some spring from the earth extremely hot, others moderately hot, others tepid, others excessively cold: they concluded from this, that all such various degrees of heat in these waters were owing either to the different degree of subterranean fire, which they had undergone; or else to the great distance, which some of them had run in the earth, after they had been sufficiently heated. They therefore maintained, that those waters particularly termed _acidulæ_ (the greatest part of which are impregnated with iron), or those, which, tho’ intensely cold, contained a large proportion of mineral matter, had in some part of the earth been impregnated with it, by means of an intense heat, which they had been gradually deprived of by a long passage thro’ the colder parts of the earth.
Some naturalists again, of a later date, having exploded the former notion as chimerical, have thought, that a vapour rising from vitriolic minerals, and mixed with the neighbouring streams of water in the bowels of the earth, has imbued them with some of the parts, and with the properties, of vitriol.
Others are of opinion, that the exhalations of vitriolic minerals, passing thro’ the cavities of the earth, are there condensed by the subterraneous cold into a limpid fluid, containing the very finest parts of that mineral salt: which fluid, mixing with the præterlabent streams of water, and issuing out of the earth with them, produce those mineral springs called vitriolic.
The last opinion I shall mention on this subject, and which indeed appears the most plausible, is of those, who think, that the iron is corroded and dissolved in these waters by means of an acid: for, as they imagine simple water incapable of doing this, they suppose, that it is first imbued with an acid in the bowels of the earth; and then, by the corrosion of the chalybeat minerals, thro’ which it runs, it comes to be impregnated with them. I once received this opinion, as the most probable I could then observe, concerning the origin of these springs: yet not as being satisfactory; for there are many objections against it, which it is difficult either to elude or to answer.
The supposition of an acidity in ferrugineous waters, I thought but ill confirmed, because, upon trial, they discover no vestiges of it, but rather appear to be alkaline. Besides, in considering the causes of mineral waters, it seems more probable, that whatever minerals they contain, they must be such, as can be received or extracted by common water in its passage thro’ the earth, by solution, abrasion, or the like simple operations; and in this way alone I think we may come to account not only for the commixtion of the saline and terrene minerals, which are found in medical waters, but likewise of those, that are metalline or sulphureous; for which simple water, at first sight, may perhaps seem to be an insufficient solvent.
It was this notion, that first induced me to make trial upon various mineral and metallic bodies, in order to know how far they could communicate their virtues to common water by infusion. I thought this might throw some light upon the origin of mineral waters; yet, tho’ I made a great many experiments of this sort, and particularly upon several kinds of native chalybeat minerals, I was as little satisfied concerning their origin as before. I at length, however, met, by accident, with what I had inquired after with so little success.
As I happened to be at a gentleman’s house near Edinburgh, in whose estate there was a great deal of coal, and who was at that time working a level or adit, in order to drain off the water, I observed, that the current of water, which flowed from this level, separated a great quantity of ochre, and, emptying itself into a river soon after it came from the entry of the level, tinged all the stones and the channel of the river, for a good way, of an ochrous colour. The taste of this water was exactly like that of a common steel Spaw; and it afforded a purple colour with galls[55]. As I knew, that this water flowed off a great body of coal, I often infused that fossil, taken from the pits near this level, in common water; but the infusions never yielded any tincture with galls. I tried in the same way another mineral, that the miners call _blaes_; which is a cliffery stratum of a blueish colour, that often lies both above and below the coal: also another fossil of a brown colour, which is very ponderous, and is called by the miners _dogger_; a thin seam of which often lies in the midst of the coal. However, neither of these would afford an infusion, that would tinge with galls. At last I got another mineral out of these coal-pits, which is sometimes found amongst the coal, but is not so frequent as any of the former; and this fully answered my expectation. It is found either in round or broad pieces, is exceeding ponderous, and of a shining yellow colour, and is called by the miners _brass lumps_. When I infused this mineral for a short time in common water, it communicated to it all the properties of a steel Spaw; its taste was exactly the same; and it received a tincture from galls, which was of a more diluted or intense purple, according to the proportion of the mineral added to the water, or to the time of the infusion. This simple experiment does therefore clearly discover to us the origin of steel waters, and the manner, in which they are impregnated with their mineral contents in the bowels of the earth.
This observation, which I had made concerning the origin of steel waters, led me, when I first visited Hartfell-Spaw, to inquire into the adjacent fossils: which was the more easily done, as the strata of the earth about the well, for a considerable depth, are exposed to view. After some search among these, I found a stratum of cliffery rock, about three or four feet thick, of a grey colour, and, I think, about twenty paces from the spring. In some of the hollow places of this rock, where the rain and wind did not reach, I observed a white saline efflorescence on its surface, which when I had taken off and tasted, I concluded, from its styptic and chalybeat taste, that it was a native vitriolum Martis, notwithstanding its white colour; but I found it, upon trial, to be alum, having some fine attenuated parts of iron conjoined with it, and the same salt with that contained in the Spaw water.
Having taken some pieces of this rock, which were quite free from the saline effervescence, and infused them in common spring-water for some hours, this water did thereby acquire the true taste of the Hartfell-Spaw. It likewise in the same manner received a deep blue tincture with galls, and contained all the other qualities of that mineral water, without the least difference, that I could observe: which, I think, ascertains the true origin of this mineral spring in the most obvious and undeniable manner.
I am persuaded, that this plain and easy method of investigating the origin of mineral springs is not only superior to the most learned discussions and elaborate theories, but will be found to be the surest, yea, the only way of extending and compleating our knowlege concerning them. As I have not yet had the opportunity of making the experiments, which I designed, upon the two fossils, that we find to be the cause of the above mineral waters, and which will be necessary to elucidate and compleat these observations, which we have made concerning their origin; I shall now only add one thing, and recommend it to the observation of others: “_Whether or not, from such a knowlege of the origin of mineral waters, we may not acquire artificial ones of as great, or perhaps of greater, medicinal use, than those, which are naturally produced?_”
XVIII. _An Account of the State of the Thermometer at the_ Hague _on the 9th of_ January 1757. _Extracted from a Letter of Mr._ Abraham Trembley, _F.R.S to_ Tho. Birch, _D.D. Secret. R.S._
[Read Mar. 3, 1757.]
Hague, Febr. 15. 1757.
I Carefully observed the thermometer during the cold days, which we have had this winter. I made use of the same thermometer, with which I made my observations in 1740, and for that purpose fixed it in the same place, where it was that year, _viz._ in a window directly exposed to the north, and open to a large square. In 1740 I saw Fahrenheit’s thermometer at two degrees below 0. This year, on the 9th day of January in the morning, it was at three degrees above 0; that is, only five degrees higher than in 1740.
XIX. _Experimental Examination of_ Platina. _By_ William Lewis, _M.B. F.R.S._
[Read Mar. 17, 1757.]
PAPER V.
THE account of this extraordinary mineral, formerly read to this illustrious Society, and honoured with their approbation, being since published in the _Philosophical Transactions_, renders any recapitulation of the discoveries hitherto made unnecessary.
The near and remarkable relation betwixt platina and gold, not only in point of gravity, but in many less obvious properties, hitherto supposed to belong to gold alone; and their as manifest disagreement in others, particularly colour, ductility, and fusibility; induced me to examine, what effects they might have in combination with one another in different proportions; and whether there is reason to credit the report of great frauds having been committed by mixing them together; how far such abuses are practicable; and, what is of more importance, the means by which they are discoverable.
_Experiments of the Mixture of Platina and Gold._
+EXPERIMENT+ I.
1. Twelve carats[56] of fine gold, and the same quantity of the purer grains of platina, were urged in a blast-furnace, for near an hour, with a fire so strong, that a slip of Windsor brick, with which the crucible was covered, tho’ defended by a thin coating of pure white clay, had begun to melt. Upon breaking the vessel, the metal was found in one smooth lump or bead; which, after being nealed by the flame of a lamp, and boiled in alum-water, appeared, both in the mass, and upon the touchstone, of a pale bell-metal colour, without any resemblance to gold. It bore several strokes, and stretched considerably under the hammer, before it begun to crack about the edges. On viewing the fracture with a magnifying glass, the gold and platina appeared unequally mixed; and several small particles of the latter were seen distinct: nor was the mixture intirely uniform after it had again and again been returned to the fire, and suffered many hours of strong fusion.
2. Eighteen carats of gold and six of platina (= 3:1) were melted together as the foregoing, in an intense fire continued about an hour. The bead, nealed and boiled, was less pale-coloured than the former, but had nothing of the colour of gold. It forged tolerably well, like coarse gold. To the naked eye it appeared uniform; but a good magnifier discovered in this, as well as in the other, some inequality of mixture, not withstanding the fusion was two or three times repeated, with the strongest degrees of heat we were capable of exciting by large bellows.
3. Twenty carats of gold and four of platina (= 5:1) were kept in strong fusion for above an hour and a half. These united into an equal mass, in which no granule of platina, or dissimilarity of parts, could be distinguished. The colour was still so dull and pale, that the compound could scarcely be judged by the eye to contain any gold. It hammered well into a pretty thin plate; but we could not draw it into wire of any considerable fineness.
4. Twenty-two carats of gold were melted in the same manner with two of platina (= 11:1) the same that standard gold contains of alloy. The mixture was uniform, of a tolerable golden colour, but easily distinguishable from that of standard gold by a dingy bell-metal cast. It worked well, was forged into a thin plate without cracking, and drawn into moderately fine wire.
5. Twenty-two carats and a half of gold, and one and a half of platina (= 15:1), melted into an uniform mass, which, after the usual nealing and boiling, proved somewhat tougher than the preceding, and of a better colour.
6. Twenty-three carats of gold were melted with one of platina; which is nearly half the proportion, that standard gold contains of alloy. The compound worked extremely well, but was distinguishable from gold by a manifest dinginess, which it retained after repeated forgings, fusions, nealings, and boilings.
7. Twenty-three carats and one-fourth of gold, and three-fourths of a carat of platina (= 31:1), formed an equal mixture, very malleable, ductile like the three foregoing whilst hot as well as cold, but not intirely free from their peculiar dingy colour.
8. A mixture of twenty-three carats and a half of gold, with half a carat of platina (= 47:1), was very soft and flexible, of a good colour, without any thing of the disagreeable cast, by which all the foregoing compositions were readily distinguishable, in the mass as well as on the touchstone, from fine or standard gold.
9. A mixture of twenty-three carats and three-fourths of gold, with one-fourth of a carat of platina (= 95:1), could not be distinguished by the eye or hammer from the fine gold itself.
In all these processes, even where the proportion of platina was small, the fusion was performed by a vehement fire, that the mineral might be the more intimately dissolved, and equally diffused thro’ the gold. The necessity of this precaution appeared from an experiment formerly related; in which one of platina having been melted with four of gold, the button appeared not much paler than standard gold with silver alloy. On a second fusion it lost its yellow colour, which had at first been only external, from an imperfect mixture, great part of the platina being concealed in the internal part of the mass, and covered as it were by a golden coat.
The crucibles were rubbed on the inside with chalk, to prevent any particles of the metal from lodging in their cavities. A little borax was employed in each as a flux; with the addition of nitre, by which the colour of gold is somewhat heightened. On remelting some of the mixtures with sundry other additions, powdered charcoal seemed to improve the colour most.
+EXPERIMENT+ II.
The preceding compositions, after being gently hammered and boiled, were weighed hydrostatically with great care, by a very tender balance, in distilled water, wherein the gravity of standard gold turned out 17.788.
All the mixtures proved heavier than standard gold. Their gravities were nearer to the medium of the gravities of the ingredients, than those of the compositions of platina with any of the other metals formerly given an account of; none falling considerably short of the mean gravity, and some rather exceeding it.
+------------------------+ | Gravity. | | By | By | |Experiment.|Calculation.|Difference. Platina | 17.000 | | Platina 1 Gold 1 | 18.140 | 18.142 | 0. 02} Platina 1 Gold 3 | 18.613 | 18.714 | 0.101} Platina 1 Gold 5 | 18.812 | 18.904 | 0.092} Platina 1 Gold 11 | 18.835 | 19.094 | 0.259} Diminution. Platina 1 Gold 15 | 18.918 | 19.142 | 0.224} Platina 1 Gold 23 | 19.089 | 19.189 | 0.100} Platina 1 Gold 31 | 19.128 | 19.213 | 0.085} Platina 1 Gold 47 | 19.262 | 19.237 | 0.025} Platina 1 Gold 95 | 19.273 | 19.261 | 0.012} Increase. Gold | 19.285 | | +-----------+------------+
+EXPERIMENT+ III.
As a mixture of platina with an equal quantity of gold has been reported to be specifically heavier than gold itself, but turned out otherwise in the above experiments; some further trials were made on that head.
1. Instead of the crude mineral, whose gravity is but 17, we took platina, that had been cupelled with lead, one of the neatest of the buttons formerly mentioned, which, tho’ retaining a portion of the lead, was nearly as ponderous as fine gold, _viz._ 19.240. This was melted with equal its weight of the gold, in a strong fire, and continued in fusion for about an hour: the mass proved spongy, and very light. We remelted it several times with vehement degrees of fire, suffering it to cool leisurely in the crucible, and, in order to separate as much as possible of the lead, to which its sponginess seemed owing, boiled it in aqua-fortis, and repeatedly injected corrosive sublimate upon it during fusion: the mass, nevertheless, still turned out cavernulous and brittle, and specifically lighter than either the gold or platina by themselves.
2. I likewise endeavoured to combine platina with small proportions of gold. By vehemence of fire, it was made to unite, tho’ not perfectly, with half its weight and less: but the mixtures were extremely spongy and brittle; in specific gravity one scarce 16, another less than 15.
3. As a cast metalline body from the Spanish West Indies, of which some account will be given hereafter, appears to have been confounded with the mineral platina, this also was melted with an equal quantity of gold. They united with great ease, by a moderate fire, into an uniform compound, tolerably compact, but whose specific gravity was only 16½; which is nearly the mean gravity of the two ingredients.
+EXPERIMENT+ IV.
As a small portion of copper somewhat heightens the colour of pale gold, platina was melted with eight times its weight of standard gold made with copper alloy. The fusion was performed, as in the preceding experiments, in a close crucible, with a strong fire, but without any flux, and continued for about an hour. The metal appeared covered with a black scurf, and had lost about ⅟200. It was much duller coloured, harder to the hammer, and cracked sooner about the edges, than mixtures of fine gold with a larger quantity of platina. By repeated fusion, and frequent nealing, it became a little softer and tougher, so as to be drawn into pretty fine wire; but the colour was still exceeding dull, more resembling that of bad copper than of gold.
The specific gravity of this compound was 17.915; a little less than the medium of the three ingredients unmixed, and a little greater than the mean gravity resulting from the platina by itself, and the copper and gold mixed; for copper, in the standard proportion, appears to diminish the gravity of gold more than it ought to do according to calculation.
From the foregoing experiments it appears, that platina is miscible with gold, in certain proportions, without injuring either its colour or ductility, or occasioning any considerable alteration in the gravity: experiments related in former papers have shewn, that it stands aqua-fortis, and the other trials by which the purity of gold is estimated. It is to be hoped, that the abuses manifestly practicable by this mineral have hitherto been but rarely made use of. To guard against them is the object of this paper; to detect them, of the next.
XX. _Experimental Examination of_ Platina. _By_ William Lewis, _M.B. F.R.S._
+PAPER+ VI.
_Experiments of distinguishing and purifying Gold mixed with Platina._
[Read Mar. 31, 1757.]
1. _By Amalgamation with Mercury._
IN an experiment related in the fourth paper, an amalgam of one part of platina and two of gold with a suitable quantity of mercury, having been triturated with water for a considerable time, and occasionally washed over, the platina was gradually thrown out, and the gold retained by the quicksilver.
Repetitions of this experiment have shewn, that tho’ the separation succeeds in some cases, it does not perfectly in all: that if there is any particle of the platina imperfectly dissolved in the gold (which will generally be the case, unless the quantity of gold is three or four times greater than that of the platina), this part will be retained, after long trituration, undissolved by the mercury, uncomminuted by the pestle, and too ponderous to be washed off in its gross form. A variety of mixtures of platina and gold were treated in the manner above described; and the gold, recovered from the amalgams, submitted to further examinations. Where the proportion of platina was large, the microscope almost always discovered still some granules of it on the fracture of the ingot: where the proportion was small, the recovered gold was frequently, but not constantly, found to be pure.