FOOTNOTES:
[1] I have been favoured by the Rev. C. Val. Le Grice, of Trereiffe, with the following extract from the Parish Register, kept at Madron:—"Humphry Davy, son of Robert Davy, baptized at Penzance, January 22, 1779." The house in which he was born has been pulled down and lately rebuilt.
[2] Soon after the days of Gibbons, the art of ornamental carving in wood began to decay, and it may now be considered as nearly lost. Its decline may be attributed to two causes. In the first place, to the change of taste in fitting up the interior of our mansions; and in the next, to the introduction of composition for the enrichment of picture-frames and other objects of ornament. "Robert Davy," says a correspondent, "has been considered in this neighbourhood as the Last of the Carvers, and from his small size, was generally called The little Carver.
[3] For these materials I acknowledge myself indebted to Dr. Penneck of Penzance, and to Mrs. Millett, Sir H. Davy's sister. The facts were communicated in letters to Lady Davy, by whom they were kindly placed at my disposal.
[4] Life of Sir William Jones, by Lord Teignmouth.
[5] Here, as Mrs. Ratcliffe would say, the Legend is so effaced by damp and time, as to be wholly illegible.
[6] "Were the enquiry diligently made," he says, "it would be found that the Goddess of Harmony has exercised more influence, however latent, over the dispensations of Themis, than her most diligent historiographers, or even her most passionate panegyrists, seem to be aware of. Every one knows how, by the ministry of Orpheus, it was she who first collected the sons of men beneath the shadow of the sceptre: yet in the midst of continual experience, men seem yet to learn with what successful diligence she laboured to guide it in its course."
[7] The original indenture, now in the possession of Mr. R. Edmonds, solicitor, of Penzance, is dated February 10th, 1795.
[8] Davy appears to have been more fortunate than his prototype Scheele; for on one occasion, as the latter was employed in making pyrophorus, a fellow apprentice, without his knowledge, put some fulminating powder into the mixture; the consequence was a violent explosion; the whole family was thrown into confusion, and the young chemist was severely chastised.
[9] M. de Bourrienne, in his "Private Memoirs of Napoleon Buonaparte," appears to have justly appreciated the influence of circumstances upon the destinies of great men. In speaking of Buonaparte at the Military College of Brienne, he says, "If the monks, to whom the superintendence of the establishment was confided, had engaged more able mathematical professors, or if we had had any excitement to the study of Chemistry, or Natural Philosophy, I am convinced that Buonaparte would have pursued those sciences with all the genius and spirit of investigation, which he displayed in a career more brilliant, it is true, but far less useful to mankind."
[10] The Land's End in Cornwall.
[11] The granite of Cornwall is generally found incumbent on primitive schistus. This is the case in many of the cliffs at the Land's End. The upper stratum is composed of granite, the lower with the surrounding rocks of schistus. D.
[12] The Islands of Scilly.
[13] A rock near the Land's End, called the 'Irish Lady.']
[14] The Irish Lady was shipwrecked at the Land's End, about the time of the massacre of the Irish Protestants by the Catholics, in the reign of Charles the First.
[15] I cannot allude to this name, without paying a tribute of respect to the memory of one who, for more than half a century, practised the profession of a surgeon in Penzance with as much credit to himself, as advantage to his neighbourhood.
[16] Bergman, Professor of Upsal, was informed of a young man who resided in the house of an apothecary, and who was reproached for neglecting the duties of his profession, while he devoted the whole of his time to Chemistry. Bergman's curiosity was excited; he paid him a visit, and was astonished at the knowledge he displayed, and at the profound researches in which he was engaged, notwithstanding the poverty under which he laboured, and the restraint under which his situation placed him. He encouraged his ardour, and made him his friend. This young man was the celebrated Scheele.
[17] No man ever entered upon an undertaking with less apparent means of success, than did Priestley upon that of Chemistry. He neither possessed apparatus, nor the money to procure it. These circumstances, which at first sight seem so adverse, were in reality those which contributed to his ultimate success. The branch of Chemistry he selected was new; an apparatus had to be invented before any important step could be taken; and as simplicity is essential in every research, he was likely to contrive the best whose circumstances obliged him to attend to economy.
[18] Dialogus de Oratoribus,—Tacit.
[19] Plutarch, in expressing the opinion of Asclepiades upon this subject, represents him as saying, that the external air, by its weight, opened its way with force into the breast. Seneca also was acquainted with the weight and elastic force of the air; for he describes the constant effort by which it expands itself when it is compressed, and affirms that it has the property of condensing itself, and of forcing its way through all obstacles that oppose its passage.—Quæst. Nat. lib. v. c. v. and vi.
[20] Here the reader will recognise the force of early associations.
[21] Brugnatelli considered that oxygen, in certain cases of combination, entered into union with different bodies, without parting with its caloric; and in that state he gave it the name of Therm-oxygen; so that Davy had a precedent for his nomenclatural innovation.
[22] Breath and life are synonymous. In the Greek, the most philosophically constructed language with which we are acquainted, this first and last act is expressed by a verb composed of alpha and omega—αω. In the Latin, the connexion between spiro and spiritus, breath and life, is evident.
[23] The only pun Davy is said to have ever made was upon the occasion of Mr. Sadler being appointed by Dr. Beddoes as his successor. "I cannot imagine," said he, "why he has engaged Sadler, unless it is that he may be well bridled."
[24] The following is the account given in his Essay. "When sulphuric acid was poured into a solution of this salt in water, a beautiful and unexpected phenomenon took place. The room was accidentally darkened at the moment this experiment was made, so that we were enabled to perceive a vivid luminous appearance. This experiment, independent of its beauty, is extremely pleasing as affording an instance of true combustion, that is, the production of Light and Heat by the mixture of two incombustible bodies." It may be presumed, that this phenomenon arose from the developement and decomposition of a portion of Euchlorine, a compound which he subsequently discovered in 1811. In the year 1813, Chevreul announced, as a new discovery, that if strontian be heated in contact with muriatic acid gas, the gas is absorbed, and the earthy salt becomes red hot.—See Annals of Philosophy, vol. ii. p. 312.
[25] It is very common, after the burning of a hay-stack, to find glass in the ashes. P.
[26] From his visit to London, as noticed at page [62].
[27] With respect to the metaphysical speculation contained in this paragraph of his letter, had he not written it in haste, we might presume he would have given a more exact expression to his ideas. By the misapplied term "Feeling of Procrastination," he doubtless meant to describe that aversion to labour which becomes habit by indulgence, and the perception of which, so far from increasing in vividness, actually languishes to obtuseness. To borrow an expression from Dr. Johnson, Davy, in his metaphysical speculations, not unfrequently trod upon the brink of meaning, where light and darkness begin to mingle.
[28] Davy here alludes to the fact of magnesian earth being prejudicial to vegetation.
[29] Lettres sur l'Angleterre, 1802.
[30] "I believe it had never been breathed before by any individual in a state so little diluted."
[31] It would thus appear that carbonic acid, in its most concentrated form, may kill by exciting a spasmodic action, in which the epiglottis is closed, and the entrance of air into the lungs altogether prevented. In a diluted form, it may destroy by its specific influence upon the blood, which would seem to be of a highly sedative character. Death produced by such an agent is probably attended with little or no suffering. The younger Berthollet destroyed his life by inclosing himself in an atmosphere of this description; and on commencing his fatal experiment, he registered all the successive feelings he experienced, which were such as would have been occasioned by a narcotic:—a pause, and then an almost illegible word occurred: it is presumed that the pen dropped from his hand,—and he was no more.
[32] On conversing with Mr. Gilbert on the above passage, I understand that it is an allusion to his opinion, that the discovery of Galvanic power would ultimately lead to a knowledge of the nature of light and heat.
[33] Mr. Gilbert no sooner discovered the tendency of Davy's opinions respecting the immateriality of Caloric, than he urged him to communicate them to Count Rumford, but he considered himself pledged to Dr. Beddoes, and his Essays were accordingly printed in the West Country Contributions. Count Rumford, it may be observed, maintained that Caloric, like Phlogiston, was merely a creature of the chemist's imagination, and had no real existence. He considered heat as nothing more than the motions of the constituent particles of bodies amongst themselves,—an hypothesis which has no claims to novelty, being perhaps one of the most ancient on record.—See his paper on Heat, Phil. Trans. for 1804.
[34] Amongst other celebrated chemists who had become acquainted with Davy at Bristol, and subsequently spoken of his extraordinary genius, was Dr. Hope. He informs me that Count Rumford had applied to him to find some chemist who would undertake the office of lecturer at the Institution; but that he failed in discovering such a person as he could, with propriety, introduce; some time afterwards, however, he became acquainted with Davy, and having soon perceived his talents, recommended him without any hesitation to the patronage of the Count. This circumstance, combined with several others, no doubt might have had its influence in deciding the fate of Davy.
[35] In England, politics so constantly mix themselves up with all our institutions, while science unfortunately finds so few disciples and patrons in the ranks of aristocracy, that every new society is viewed with jealousy and party spirit. Johnson says, in his Life of Addison—"It has been suggested that the Royal Society was instituted soon after the Restoration, to divert the attention of the people from public discontent."—P.
[36] He alludes to some calculations connected with light, and the imponderable fluids.
[37] He delivered his farewell Lecture on the 9th of the same month.
[38] From the following minute it would appear, that Dr. Young's connection with the Royal Institution was but of short duration. It will be remembered that his appointment took place on July 6, 1801.
"Resolved—That Dr. Young be paid the balance of two years' complete salary, and that his engagement with the Institution terminate from this time—July 4, 1803."
[39] I have lately been informed that the idea of constructing an instrument like the Camera Lucida, first suggested itself to Dr. Wollaston, on his noticing certain phenomena occasioned by a crack in the glass before which he was shaving himself.
[42] Récherches sur les Lois de l'Affinité.—Mém. de l'Institut National, Tome III. p. 5.
[43] The masterly manner in which he combated the successive arguments of Berthollet upon this question is admirable. In the first place, he attacked the theory upon general principles, and then exposed the fallacy of the several experiments adduced in its support. "Were the proposition correct, that in all cases of decomposition in which two bodies act upon a third, that third is divided between them in proportion to their relative affinities, and their quantities of matter, it is quite evident that there could be scarcely any definite proportions: a salt crystallizing in a strong alkaline solution would be strongly alkaline; in a weak one, less alkaline; and in an acid solution it would be acid." With regard to glasses and alloys, adduced by M. Berthollet as compounds of indefinite proportions, Davy answers—"It is not easy to prove, in such cases, that the elements are chemically combined, for the points of fusion of alkali, glass, and certain metallic oxides, are so near to each other, that transparent mixtures of them may be formed." The experiment upon which M. Berthollet laid great stress, viz. that a large quantity of potash will separate a small quantity of sulphuric acid from sulphate of baryta, Davy invalidates in a most complete manner. He says—"This experiment was made in contact with the atmosphere, in which carbonic acid is always present; and carbonate of potash and sulphate of baryta mutually decompose each other."
[44] Catechu is an extract obtained from the wood of a species of the Mimosa that grows in India, by boiling and subsequent evaporation. It is of two kinds; one from Bengal, the other from Bombay. The former contains rather less, the latter rather more, than half its weight of tannin. The remainder in both cases is a peculiar extractive matter mixed with mucilage.—P.
[45] In the 40th volume of the "Annals of Agriculture," an account is given of the Holkham Sheep-shearing for 1803, and in the list of the company is the name of "Mr. Professor Davy."—At the meeting of 1808, he was also present, and is mentioned as the great chemist, whose discoveries will immortalize his name. Mr. Coke, in the course of his speech after dinner, alluding to the question of long and short dung, said, "It is the opinion of a friend of mine, who sits near me, Professor Davy, and upon whose judgment, on account of his extensive chemical as well as other scientific knowledge, I place the highest reliance, that the manure carried immediately on the field, without being disturbed, will have a greater effect in exciting rapid vegetation, and in encouraging the growth of the turnip plant, than when applied in the ordinary manner; for, under such circumstances, it will not only be more moist and alkaline, but it will be protected from a loss of substance, amounting very nearly to one-third of its original bulk." Davy afterwards, in company with the Duke of Bedford, Lord William Russell, Lord Thanet, Sir Joseph Banks, and other agriculturists, inspected several farms.—In 1812, his health was drunk at the Woburn Sheep-shearing by the Duke of Bedford; and in the following festival it was proposed by Lord Hardwicke.
In the print of the "Woburn Sheep-shearing," published by Garrard, in 1811, No. 75 represents Davy; he is standing, in a listening attitude, behind Mr. Coke, who is conversing with Sir Joseph Banks, Sir John Sinclair, and Mr. Arthur Young.
[46] "The Honey Moon" was produced at Drury Lane, on Thursday, the 30th of January, 1805.
[47] The subject was "Julia's Eyes."
[48] I am assured by one of his earliest friends, that, at this period, he did not appear even to have an idea of the value of property. Any thing not immediately necessary to him he gave away, and never retained a book after he had read it.
[49] He alludes to a rich piece of land near the river Parrot; a specimen of the soil of which Mr. Poole had sent him for analysis.
[50] Gregory Watt was one of those philosophers to whose memory justice has not awarded its due. He was a meteor, whose light no sooner flashed upon us than it expired. His paper upon the gradual refrigeration of Basalt, alone entitled him to a distinguished rank amongst experimentalists. It was read before the Royal Society in May; and he expired in the following October.
[51] There are some circumstances of interest connected with the history of this young man. He possessed much chemical talent; but during his residence in Ireland he was converted to the Catholic religion, and is at this time a Catholic priest in some part of the Continent.
[52] He means that the middle-men being discontinued, their large allotments should be divided into farms of convenient extent, the occupiers of which should rent immediately from the owners of the soil.
[53] The simple fact relating to the action of metals on the animal organs was certainly not first observed by Galvani, but by Sulzer, who has described the sensation of taste produced by the contact of lead and silver with the tongue, in his Théorie des Plaisirs, in 1767.
[54] M. Humboldt (Ueber die gereize Faser, l. 473, 1797,) quotes part of a letter from Dr. Ash, in which it is said that, "if two finely polished plates of homogeneous zinc be moistened and laid together, little effect follows; but if zinc and silver be tried in the same way, the whole surface of the silver will be covered with oxidated zinc. Lead and quicksilver act as powerfully upon each other, and so do iron and copper. M. Humboldt says, that, in repeating this experiment, he saw air bubbles ascend, which he supposes to have been hydrogen gas from the decomposition of water.
[55] As this lecture will be frequently mentioned in the progress of these Memoirs, in connexion with most important discoveries, it may be interesting to the reader to learn something of its foundation and design. I have therefore collected the necessary information from the Minutes of the Royal Society. Mr. Baker is well known in the history of Science, as an accurate observer with the microscope, and as the author of several works on the subject. By his will, dated July 1763, he bequeathed the sum of one hundred pounds, the interest of which he directed "to be applied for an Oration or Discourse, to be read or spoken yearly by some one of the Fellows of the Royal Society, on such parts of Natural History, or Experimental Philosophy, at such time, and in such manner, as the President and Council of the said Society shall please to order and appoint; on condition, nevertheless, that if any one year shall pass after the payment of the said hundred pounds, without such oration or discourse having been read or spoken at some Meeting of the said Royal Society, the said hundred pounds shall then become forfeited, and shall be repaid by the said Society to his executors," &c. Baker died in November 1774, and in the following year a Fellow was nominated to read the lecture. It is a whimsical circumstance, that the first lecturer should have been Peter Woulfe, the last of the alchemists. The names of the successive lecturers were as follow:—Dr. Ingenhouz, Mr. Cavallo, Mr. Vince, Dr. Wollaston, Dr. Young, Sir H. Davy, Mr. Brande, Captain Kater, Captain Edward Sabine, and Mr. Herschel.
[56] Nicholson's Journal, vol. iv. p. 190.
[60] M. Bonijol of Geneva has lately succeeded in effecting the decomposition of Potash and the Chloride of Silver by ordinary electricity. His process consists in placing these substances in a very narrow glass tube, and in then passing a series of electric sparks from the ordinary machine through them. The electricity was conducted into the tube by means of two metallic wires fixed into the ends. When a quick succession of electric sparks had taken place for about five or ten minutes, the tube containing chloride of silver was found to contain reduced silver; and when potash had been submitted to the electric current, then the Potassium was seen to take fire as it was produced. The same philosopher has likewise contrived to decompose water by atmospheric electricity. The electricity, in this case, is collected from the atmosphere by means of a very fine point fixed at the extremity of an insulated rod; the latter is connected with the apparatus, in which the water is to be decomposed, by a metallic wire, of which the diameter does not exceed 1-50th of an inch. In this way the decomposition of the water proceeds in a continuous and rapid manner, although the atmospheric electricity be not strong. Stormy weather, it is said, is quite sufficient for the purpose.—Bib. Univers. 1830, p. 213. and Royal Institution Journal, No. 2.
[61] It is perhaps a fact not very generally known, that glass, to a certain extent, is decomposable by water: if some of it in a powdered state be triturated with distilled water, in a short time the turmeric test will indicate a portion of alkali in solution.
[63] It will be sufficient for my present purpose to point out those existing between Chlorine, Iodine, and Bromine.
[65] Reflecting upon this and similar facts, it has occurred to me that Voltaic electricity might be applied for removing the blue colour in the skin, occasioned by the internal use of nitrate of silver. I hope to be able very shortly to submit this theory to the test.
[66] During the contentions of the Neptunists and Plutonists, alluded to in a former part of this work, specimens were produced exhibiting the intermixture of mineral bodies, which was completely hostile to all theory. These anomalies now receive a plausible explanation from the agencies of Voltaic electricity.
[67] The History and Present State of Electricity; by Jos. Priestley, LL.D. F.R.S., &c. London, 1795.
[68] Dr. Priestley augured much from the talents of Davy. After the publication of his first paper on Galvanism, he wrote to him from America, and expressed the pleasure he felt on finding his favourite subject in such able hands. Priestley died in 1804, and therefore did not witness Davy's success.
[69] A most remarkable illustration of this fact occurs in the history of Locke, who certainly came as near to an important discovery as any philosopher who ever caught a glimpse of a truth without seizing it; but his statement did not, in any degree, hasten the developement of that new branch of science which was reserved for the genius of Dr. Black to investigate, and who a century later, by the discovery of fixed air, changed the whole face of Chemistry. The passage to which I allude is extracted from the Life by Lord King, and is so curious, that I shall give it a place in this note. "M. Toinard produced a large bottle of Muscat: it was clear when he set it on the table; but when he had drawn out the stopper, a multitude of little bubbles arose, and swelled the wine above the mouth of the bottle. It comes from this, that the air, which was included and disseminated in the liquor, had liberty to expand itself, and so to become visible, and, being much lighter than the liquor, to mount with great quickness.—Quere, Whether this be air new generated, or whether the springy particles of air in the fruit, out of which these fermenting liquors are drawn, have, by the artifice of Nature, been pressed close together, and there by other particles fastened and held so; and whether fermentation does not loose these bands, and give them liberty to expand themselves again? Take a bottle of fermenting liquor, and tie a bladder on the mouth.—Quere, How much new air will it produce; and whether this has the quality of common air?"
Another instance equally illustrative of the manner in which important truths will sometimes elude notice, even after Science has approached so near as to touch them, is presented in the history of the Barometer. Toricelli, the pupil of Galileo, while reflecting upon the phenomenon which had so greatly perplexed his master, viz. that water could not be raised above thirty-two feet in the body of a pump, rightly conjectured that the water, under such circumstances, was not drawn, but pushed up into the barrel, and that it could only be so pushed up by the force of the atmosphere. It then occurred to him, that if mercury were used instead of water, being heavier, it would not be pushed up so high by the weight of the air. So, taking a glass tube of about three feet in height, made air-tight at one end, he first filled it completely with quicksilver, and then closing it with his finger, reversed it in a basin containing that metal; when he had the gratification of seeing the liquid in the tube descend, as he had anticipated. Here then was the discovery of the Barometer; but it was reserved for another to find out that such an instrument had been actually invented. Pascal first made the remark, that the inference of Toricelli, if true, might be confirmed by carrying the mercurial tube to a considerable elevation; when the atmospheric column being diminished, that of the mercury, which was supposed to be its balance, ought likewise to be shortened in a corresponding proportion. It followed then, that a measure of the weight of the atmosphere, in all circumstances, had been obtained, and consequently that of the height of any place to which the instrument could be carried. In this manner was a discovery completed, which had for ages escaped the greatest philosophers who had made the nearest approaches to its developement.
[70] "À celui qui, par ses expériences et ses découvertes, fera à faire à l'Electricité et au Galvanisme un pas comparable à celui qu'ont fait faire à ces Sciences Franklin et Volta."
My French correspondent adds, "Ces soixantes mille francs n'ont pas été adjugés, le pas n'ayant point été fait."
[71] The propriety, and even the necessity, of such a compact become daily more apparent, as our knowledge of bodies extends. If we were to degrade a substance from its class, in consequence of the absence of some one quality which enters into its more perfect examples, we should soon find ourselves involved in paradoxes.—What idea, for instance, could we form of an acid?—Its sourness?—Prussic Acid—Arsenious Acid, are not sour.—Its tendency to combine with an alkaline or earthy base?—If so, sugar is an acid, for it combines with lime. I remember a chemist having been exposed to much ridicule from speaking of a sweet acid—Why not?
[72] In the language of Darwin, we should say, that the simple ideas of weight and lustre, which form the complex idea of a metal, have become so indissoluble, that they can no longer be separated by volition. The principle admits of many familiar illustrations, and is the source of numerous fallacies. When any one voluntarily recollects a Gothic window, which he had seen some time before, the whole front of the Cathedral occurs to him at the same time: in like manner, the taste of a pine-apple, though we eat it blindfold, recalls the colour and shape of it. Coleridge has made a good remark upon this subject. He says, "It is a great law of the imagination, that a likeness in part tends to become a likeness of the whole." It is thus that we trace images in the fire, castles in the clouds, and spectres in the gloom of twilight.
[73] If we are disposed to enter into a more critical examination of the subject, we shall find that, although the above is a general expression of the change produced, there are subordinate actions of a more complicated nature: the metal, in the first place, decomposes a portion of the water, in order to combine with its oxygen, and form potash, which in its turn has a powerful affinity for water; the heat arising from two causes, decomposition and combination, is sufficiently intense to produce the inflammation. Water is a bad conductor of heat; the globule swims exposed to air; a part of which is dissolved by the heated nascent hydrogen; and this gas, being capable of spontaneous inflammation, explodes and communicates the effect of combustion to any of the bases that may be yet uncombined. The manner in which the potassium runs along the surface of water may be compared to a drop of water on red-hot iron; in the one case the hot potassium, in the other the cold water, is enveloped in an atmosphere of steam.
[74] In his Bakerian Lecture of 1810, he informs us that he obtains Sodium by heating common salt, which has been previously ignited, with Potassium—an immediate decomposition takes place, and two parts of Potassium produce rather more than one of Sodium.
[75] Many years afterwards, when Davy was travelling on the Continent, a distinguished person about a foreign court, enquired who and what he was; never having heard of his scientific fame. Upon being told that his discoveries had revolutionized Chemistry, the courtier promptly replied—"I hate all revolutionists—his presence will not be acceptable here."
[76] On the same day he decomposed Soda with somewhat different phenomena.
[77] He alludes to a Paper, entitled "On the Quantity of Carbon in Carbonic Acid, and on the Nature of the Diamond; by William Allen, Esq. F.R.S. and William Hasledine Pepys, Esq." Communicated by Humphry Davy, Sec. R.S. M.R.I.A. Read June 16, 1807.
[78] He here alludes to a train of research, which will be considered hereafter.
[79] This observation relates to the magnificent battery constructed by Mr. Children, of which he presented an account to the Royal Society, in a Paper read in November 1808, entitled, "An Account of some Experiments, performed with a view to ascertain the most advantageous Method of constructing a Voltaic Apparatus, for the purpose of Chemical Research. By John George Children, Esq. F.R.S." The great battery described in this Paper consisted of twenty pairs of plates, each plate being four feet high by two feet wide: the sum of all the surfaces was ninety-two thousand one hundred and sixty square inches, and the quantity of liquid necessary for charging it, one hundred and twenty gallons. At the same time he constructed another battery, which consisted of two hundred pairs of plates, each being only two inches square. In the one case, then, he commanded extent of surface, in the other, extent of number; and by a series of comparative experiments, he fully established the theory of Davy (page [246]), that the intensity of Electricity increases with the number, and the quantity with the surface.
[80] The Pyrophorus of Homberg, of which a description is to be found in the Mémoires de l'Academie, for 1711, was made by mixing together any combustible body, as gum, flour, sugar, charcoal, &c. and alum, and then, after roasting the mixture till it was reduced to a dry powder, exposing it in a matrass to a red heat. In this process, the theory of which was first explained by Davy, the potash of the alum is converted into potassium, which, by its absorption of oxygen from the atmosphere, generates heat, and sets fire to the charcoal contained in the powder.
[81] The 'Potassa Fusa' of our Pharmacopœia generally contains a small proportion of the peroxide, and will therefore effervesce when thrown into water.
[82] I received the above jeu d'esprit from the late learned Orientalist, Mr. Stephen Weston, only four days before his death. Since its publication in the first edition of this work, a chemical friend sent me the following improved version of it.
Says Davy to Baryt, "I feel strong temptation
To effect by my art your deoxidation;
And the money I've got in my pocket I'll bet all,
I prove you a true, though disguised lad of metal."
Says Baryt to Davy, "A truce to your mirth;
If you turn me to metal, I'll turn you to earth;
So moisten your clay, don't improve Science daily,
Nor treat me as you've treated poor Soda and Kali."
[84] The late interesting experiments of Mr. Daniell "on the action of Mercury on different Metals," which have been recently published in the first number of a new series of the Journal of the Royal Institution, appear to throw much light upon this subject. By agitating a few grains of spongy platinum with mercury in water acidified with acetic acid, he obtained an amalgam of the consistence of soft butter, which retained its consistence for many weeks, and greatly resembled that formed by the electrization of mercury in contact with ammonia. When the amalgam was laid upon filtering paper, the moisture was gradually absorbed and evaporated, and the mercury returned to a fluid state. By a more refined experiment, Mr. Daniell ascertained that the process was accompanied by the evolution of hydrogen gas; whence he very fairly concludes, that, when minutely divided, platinum is agitated with mercury, and moisture is present, an electrical action takes place, which, when heightened by the addition of a diluted acid, or the solution of a neutral salt, is sufficiently energetic to decompose water and evolve hydrogen: the oxygen at the same time combines with the mercury, and a solution is effected by the acetic acid, which its unassisted affinity could not have produced. "It also appears," continues Mr. Daniell, "that this electrical action communicates an adhesive attraction to the particles of the metal, by which the particles of liquid and aëriform bodies are entangled and retained, a kind of frothy compound formed, and the fluidity of the mercury destroyed. The appearance of this amalgam is so very like that of the ammoniacal compound formed by exposing a solution of ammonia in contact with mercury to the influence of the Voltaic pile, or when an amalgam of potassium and mercury is placed upon moistened muriate of ammonia, that it is impossible not to be struck with the resemblance. Mr. Daniell is therefore inclined to believe that the production of the latter may be explained upon the same principles as that of the former. When the effect is produced by the direct application of the electrical current, by means of the battery, it ceases the moment the connexion between the poles is broken; and when brought about by the agency of the amalgam of potassium, the electrical action is doubtless excited by the contact of the two dissimilar metals, and the frothy compound lasts no longer than the existence of the potassium in the metallic state; whereas in the action between mercury and finely divided platinum, the permanence of the metals produces a much more lasting effect, and the soft amalgam may therefore be preserved for a greater length of time.
[85] "On the Electro-chemical Decomposition of the Vegeto-Alkaline Salts." In this communication, the Professor gives an account of some experiments of his own, with a view to ascertain whether the vegetable alkalies, if electrised in contact with mercury, would impart any principle to the latter metal. In experiments with morphia and cinchonia, in which the mercury in contact with the vegetable base was rendered negative, not the least change in the fluidity of the metal could be perceived. When, however, a similar experiment was made with quina, the metal became filmy, and acquired even a tendency to a butyraceous appearance, but the phenomenon was found to depend upon the presence of a minute portion of lime.
[86] The difficulty of seizing upon elementary forms, as well as the infinity of combinations of which they are susceptible, are supposed by Mr. Sankey to be allegorized in the fable of Proteus, Πρωτεισς, being derived from πρωτσς, signifying the first element. It is not a little singular that Mr. Leslie, to whom such a speculation was wholly unknown, should have recognised in the same fable a picture of the cautious but intrepid advances of the skilful experimenter: he tries to press Nature into a corner,—he endeavours to separate the different principles of action,—he seeks to concentrate the predominant agent, and labours to exclude as much as possible every disturbing influence. Notwithstanding the confidence with which modern philosophers have claimed the discovery, the experimental mode of investigation was undoubtedly known and pursued by the ancients, who appear, observes Mr. Leslie, to have concealed their notions respecting it under the veil of allegory. Proteus signified the mutable and changing forms of material objects; and the inquisitive philosopher was counselled by the Poets to watch their slippery demon, when slumbering on the shore to bind him, and to compel the reluctant captive to reveal his secrets.—Elements of Natural Philosophy.
[87] Berthollet first applied oxymuriatic acid for the purpose of bleaching, in France; from whence Mr. Watt introduced it into England.
[88] Dr. Thomson has more recently explained the operation, by supposing that water is decomposed, and that its hydrogen goes to the chlorine, and its oxygen to the water, forming with the latter a deutoxide of hydrogen, or the oxygenated water of Thénard, which he considers as the true bleaching principle.
[89] Experience has not confirmed the value of this suggestion. Davy imagined that the vegetable fibre was injured by the saline residuum; and having found that muriate of magnesia was less corrosive than muriate of lime, he was led to propose the substitute above stated. The fact, however, is, that the fibre is injured by the chlorine; and as this body has only a slight affinity for magnesia, it too quickly abandons it; and consequently the oxymuriate of lime is still preferred.
[90] From ευ and χλωρος.
[91] The most vivid effects of combustion known are those produced by the condensation of oxygen, or chlorine: but in this instance, a violent explosion with heat and light is produced by their separation, and expansion; a perfectly novel circumstance in chemical philosophy.
[92] A little reflection will convince us that such a nomenclature could never have been adopted with propriety. It is in direct defiance of the Linnæan precept, that a specific name must not be united to the generic as a termination; besides which, such terms could never have been preserved in translations into other languages.
[93] For an admirable paper upon this subject by Mr. R. Phillips, in which all the material points of the subject are considered with that acumen which distinguishes its author, see Annals of Philosophy, vol. i. New Series.
[94] Sir Humphry Davy, during some experiments on the diamond, subsequently ascertained that less than 100th of a grain of water is sufficient to produce a sensible dew on a polished surface.
[95] Royal Institution Journal, vol. i. p. 283.
[96] There were four hundred tickets issued for the Course, sixty of which were honorary; the produce of the remainder amounted to 672l. 5s. 3d. Davy received 525l.; and the surplus went to officers and servants, and for the discharge of incidental expenses.
[97] These Courses were more numerously attended than those in 1810, there having been issued about five hundred and twenty-five tickets; the proceeds of which were 1101l. 2s.
[98] In February 1812, he exhibited a model, in one of his lectures at the Royal Institution, in illustration of his plan; from which it appeared that the air deteriorated by respiration was conducted through three copper pipes, terminating in a single tube, to the roof of the building; and by means of ventilators below, there was a constant supply of fresh air, the circulation of which was promoted by a furnace.
[99] "Elements of Chemical Philosophy," to be presently noticed.
[100] Specimens of substances ejected from the crater in that island, which Mr. Clayfield forwarded to Davy, in consequence of having heard that he had been engaged in examining the sand collected at Barbadoes, and which was a product of the same eruption.
[102] Iodine, Fluorine, &c. had not been discovered at this period.
[104] See his Salmonia, Edit. 2. p. 9.
[105] Edinburgh Review, vol. 22, page 253.
[106] For example:—What weight of wheat is equivalent to a given weight of oats, barley, rye, &c.? Suppose three hundred pounds of potatoes feed twenty head of cattle for any given time, how many will the same weight of oats feed?
[107] The history of his native county would have furnished him with a parallel instance of the intelligence and design which Nature displays in connecting the wants and necessities of the different parts of creation, with the power and means of supplying them. In a primitive country like Cornwall, the siliceous soil necessarily requires much moisture, and we may perceive that the cause which occasions, at the same time supplies this want; for the rocks elevated above the surface, solicit a tribute from every passing cloud; while in alluvial and flat districts, where the soil is rich, deep, and retentive of moisture, the clouds float undisturbed over the plains, and the country frequently enjoys that uninterrupted series of dry weather which is so necessary to its fertility. Linnæus observes, that the plants which chiefly grow upon the summit of mountains, are rarely found in any other situation, except in marshes, because the clouds arrested in their progress by such elevations, keep the air in a state of perpetual moisture.
[108] January 1813.
[109] Edinburgh Review, vol. xxii. p. 270.
[111] These facts have been confirmed by agriculturists, who could not possibly have had any favourite theory to support. Dr. Fenwick tells us, (Essays on Calcareous Manures, p. 11. 1798,) that in the county of Durham, the farmers always distinguish between hot and mild limes. They never apply the former to exhausted lands, or to any soil that has been long under a course of tillage, unless it be very deep and rich. In peaty soils, and in new, sour, and wild lands, the hot limes, on the contrary, are preferred to the mild ones. Dr. Fenwick made some experiments to ascertain the cause of the differences between these varieties of lime; and though he failed to discover that by analysis which Mr. Tennant subsequently ascertained, he nevertheless arrived at a just conclusion by simple observation; and was led to believe, that "what farmers term hot limes, are such as re-absorb their fixed air more slowly, and therefore continue longer to exert the peculiar action of quicklime."
[112] When this substance was first introduced into America, which is nearly forty years since, it was imported from the quarries of Montmartre, and in such request was it, that a bushel of wheat was usually given for the same measure of gypsum: it is now, I believe, obtained from Nova Scotia; I have not heard that it has been found within the States. It may perhaps serve to convey some idea of the extent to which it has been applied, when I state, that Mr. Maclure assured me that not less than three hundred vessels are constantly employed in the traffic, and that in Philadelphia twenty merchants, at least, are engaged in supplying the demand for it. Its efficacy appears to be considerably increased by applying it in a minute state of division; and a want of attention to this circumstance may possibly have been one of the causes which have rendered its advantages less conspicuous in England. In America, three or four hundred mills, of a peculiar construction, have been erected in different parts for the purpose of grinding it.
[113] Gypsum is readily produced by the admixture of decomposing pyrites and calcareous matter: in proof of which the Mineralogist can produce specimens of oyster shells studded with crystals of selenite from Shotover; and alum from the aluminous shale at the Hurlet Mine near Glasgow.
Transcriber's note:
Minor spelling and punctuation inconsistencies been harmonized. Obvious printer errors have been repaired. Missing page numbers are page numbers that were not shown in the original text.
The formatting of the letters has been regularized.
Every effort to decipher the hand written letter by Sir Humphry Davy has been made, however, there are no guarantees that it is correct.