812 model Das sind than silver. It is so malleable that even when alloyed with copper, in the proportion of three grains to an ounce, it can be beat so thin, that gold-leaf is only 1-282,000th of an inch thick. It would be still more malleable without the copper; and when employed to gild silver wire, it is found by computation to be only 1-12th part as thick as goldleaf. When viewed in this state with a microscope, it shows no cracks. An ounce of gold or silver wire is capable of being extended, according to the statement in Lewis's Philosophical Commerce, 1300 miles in length. In tenacity and strength gold comes after iron, copper, platinum, and silver. It requires a heat twice as great as mercury to melt it, and is so diffi cult of volatilization that for a long time it was regarded as perfectly fixed. It may be exposed for a long time to a great heat, and to air, without undergoing any alteration. Powerful burning-glasses, however, as well as flame urged on it by a stream of oxygen, have effected its volatilization. Electricity converts it into a purple oxide. Franklin, who first performed this curious experiment, found, when gold-leaf was placed between two thin plates of glass, leaving both ends hanging out, and an electrical shock was transmitted through it, that the of the gold becoming brittle by the addition of the smallest quantity of this metal. It is even said that gold is deprived of its ductility by merely keeping it, while fused, near bismuth raised to the same temperature. The purpose of alloying gold with silver and copper, as is the case in Britain, where the gold coin contains 1-12th of these less valuable metals, is to add to its hardness and durability. This alloy, it has been ascertained, suffers much less from friction than pure gold, and the stamp is not so liable to be obliterated. An alloy of gold and silver being more fusible than gold, is employed to solder pieces of it together. PLATINA, or PLATINUM, for this name is written both ways, was first discovered to be a distinct metal about the year 1749. For a knowledge of it, therefore, and of its many valuable properties, we are indebted to the moderns, and chiefly, indeed, to our cotemporaries. Mr. Wood was, we believe, the first person to make it known, and since his time its nature has been investigated by several chemists. It was first found in Choco, in Peru, and in the mine of Santa Fe, near Carthagena; and it has lately been discovered in the silver mines of Guadalcanal, in vince of Estramadura, Spain. and the glass was tinged with pur- 'gold-leaf disappeared in places, It has also been found Bra zils, and always in the same state of native platinum, and consisting of scales or grains. In 1814, al mass weighing 1lb. 9oz. Idrm., was picked up in Quebrada de Apoto, in the province of Notiva, govern ment of Choco, in South America. This was considered so great a curiosity, that it was presented by its proprietor, Dr. Ignacio Hurtado, to the king of Spain, and it is~ now deposited in the Museum at Madrid. Platinum is not, therefore, very plentiful, and the ore which has been discovered is always accompanied by four other new metals, which we shall afterl wards describe. It is brought from America in the same state as it is found, and is then very impure, containing several other metals. t To purify it the platinum is dissolved in nitro-muriatic acid, with as little heat as possible; the solution is poured off the undissolved matter, and the platinum is precipitated by muriate of ammonia. Wash the precipitate, and expose it to a heat raised slowly to redness. By redissolving it and repeating the process, you obtain pure platinum in grains; they are wrapped in a thin plate of the same substance, heated, and cautiously hammered till they are formed into an ingot. Platinum, thus purified, is the heaviest body we are acquainted with. Its colour is the same as that of silver, but it is not so brilliant. It is harder than either gold, silver, or copper, but not so hard as iron. It is capable of being welded like iron, but is one of the most infusible of metals, and requires the strongest artificial heat we can produce to melt it. Exposure to air has no effect on it; and the only acid which attacks it is a mixture of one part nitric and three parts muriatic acids. In ductility and malleability it is perhaps inferior to gold, but superior to all other metals. Platinum unites with oxygen, and one of its oxides has been recommended by Mr. Cooper, as a valuable addition to the colours of enamellers, as it is not reduced when heated with enamellers' flux. Platinum forms alloys with the other metals, only one of which appears to have been put to any use, or to possess any interest. Tin, indeed, unites with platinum, showing considerable chemical action. If a piece of tin foil and platinum are wrapped up together, and exposed to the action of the blow-pipe, or a lighted candle, they combine immediately, and give out both light and heat. A very small quantity of platinum added to copper, renders it of a golden colour, makes it harder, of a finer grain, and not so liable to corrosion. alloy of this description, with a little silver, is at present employed in the manufacture of Mr. Stansbury's patent locks, and contributes to their durability. Platinum An is obtained in too small quantities, and is too difficult to work, to be put, at present, to many uses. Its valuable properties, uniting the indestructibility of gold with the hardness of iron, point it out, however, as well adapted to a variety of purposes. From resisting the action of heat, and the most concentrated acids, it is peculiarly useful when formed into some chemical instruments, such as crucibles,small tongs, rods, &c. On the other hand, it is speedily corroded by caustic alkalies, and even neutral salts, contained in minerals, have been known to injure platinum vessels. It has, indeed, been said, that a Mr. Strauss has discovered a mode of applying it, with as much ease as tin, to the inside of copper vessels, which, could it be effected, would be of considerable utility. Perhaps the most valuable use to which platinum has yet been put is to furnish a light to the miner, when any ordinary lamp would either be extinguished or subject him to an explosion. The moment the common light in the safetylamp is extinguished by the superabundance of carburetted hydrogen gas, a coil of platinum wire, suspended over it, becomes red hot, and affords light enough for the men to find their way back from the threatened danger. When they return to where the air contains less than 1-4th of carburetted hydrogen, the lamp is rekindled by the wire. This property also has been taken advantage of to make an instantaneous fire machine, by exposing platinum to the action of a stream of hydrogen gas. The invention for this purpose, as well as the temperature at which the incandescence of the platinum wire takes place, have already been described in No. III. and No. XI. of the Chemist. QUERIES. To the Editor of the Chemist. MR. EDITOR,-Can you account for the following phenomenon, if it be such? I put by a very strong solution of common salt, after purifying it by carbonate of soda, as suggested by Dr. Henry, to crystallize, in an evaporating dish, which I placed on a shelf. After some days, I found partial and imperfect crystals on the outside of the dish, and that the place on which it rested was completely wet. I dried the place, and replaced the dish where it had been before. The same appearance of wet was, in a few days, renewed, and wiped away again. I then, instead of placing the dish containing the solution on the shelf, put another empty dish under it, smaller than the first, to prevent the bottom of the first dish from resting on the * inside of the other; and in a few 'days I perceived some of the solustion in the under dish; but, on a careful examination of the bottom and sides of the upper dish, I could not see any thing like the appearSance of wet. Now, Qu. 1. How did this portion of the solution escape from the upper to the lower dish? by capillary attraction, or how otherwise? Qu. 2. How is it that no appearance of wet was visible on the out-side of the upper dish? uth An answer to these inquiries, if they deserve it, will oblige A constant reader, CHEMICUS IGNORAMUS. *July 2. US. We thought there was something quite inexplicable in the foregoing circumstance, and requested to be informed if no fact had been omitted. The following additional letter came. We should still beg to ask our Correspondent, what distance the solution was below the edge of the dish, and if the pasteboard was wet?-ED. SIR, I did state all the particuIlars which appeared to me to have an influence on the phenomenon I described. But it has since occurred to me, that I should have mentioned my placing a card or piece of pasteboard loosely over the dish containing the solution, though this does not suggest to me a sufficient account of the external crystalliza tion. Not above one or two crystals formed on the under side of the card. On one or two of the very warm days we have lately had, the outside of the dish containing the solution was wet, and even a large drop of it might be seen at the bottom of the dish ready to fall; but at other times (last night and this morning early, for instance,) nothing of the sort was visible, on the most careful examination of the outside and bottom of the dish. It is, therefore, I think, evident, that the appearances I have noticed are materially influenced by the different states of the atmosphere. The crystallization on the outside is chiefly confined to those parts of the dish which have been most exposed to the light and air coming from the window, the opposite side of the dish, being near the wainscot of the light closet where I have kept it, having no crystals upon it. The crystallization is thickest and most imperfect at the top, towards the rim or upper edge of the dish, where it is now quite in lumps in one or two places. Lower down the outsides, the crystallization, as far as it extends, is much more perfect. The crystallization on the inside is nearly all round, pretty equal, and much less thick than that on any part of the outside. There are a few separate perfect crystals (cubes) to be seen on the inside. I have hitherto been speaking of the largest of the two dishes, and in which the solution was originally placed. There has been no appearance whatever of wet.or crystallization on the outside of the smaller or under dish, on which I placed the larger one; nor is the portion of the solution in that dish considerable, perhaps 30 or 40 drops, and which shows no tendency to crystallize. It is as salt as the solution in the upper dish, for I tasted it; so that it is certainly not by mere evaporation that the liquid has escaped from its original situation, in which case, I apprehend, the evaporated, I remain, as before, July 13. ANSWERS TO QUERIES. To the Editor of the Chemist. MR. EDITOR, Having observed some strange questions in your 17th Number, as to light, I take the liberty of sending you the following answers. In doing it, Sir, I must observe that we are all more ready to discuss those subjects which lie, perhaps, beyond the reach of man, than those open to his investigation. The fact is, that the fancy is at full liberty of exerting itself on all matters which cannot be brought to the test of experiment, and on such, therefore, we are all free to hazard conjectures, and give explanations, because we have no dread that any person acquainted with the subject can prove our conjectures erroneous, or our explanations absurd. Juvenis's question as to the sun being the primary or secondary source of light, seems of this nature; and, according to the principle just mentioned, I am ready to reply to it, while I have frequently passed by, thinking they might be answered by any body, several questions of a more useful nature. Perhaps, too, Juvenis's question carries an answer with it, when it is closely examined. The term light, Sir, means only the unknown cause of vision; it is not felt, it cannot be weighed, it has no extension, nor is light itself seen. Thus, therefore, to reply to Juvenis's third question, first, the light is proved, by our applying the same term to it, to be the same whether emitted during combustion, or proceeding from the sun. The term means only the unknown cause for 'perceptions of sight; and its effects, namely, these perceptions, being the same, we pronounce the cause to be the same. To come now to Juvenis's second question: in ordinary language, reflected light is light proceeding from one body to another, and sent back from it. Does Juvenis know any body which sends its light to the sun? Till he or some other person discovers one, it must be admitted that light is not reflected from the sun. As to Juvenis's second question, whether heat proceeds or not from the same source, it is so difficult to answer, that I must leave it to some more acute Correspondent. I am, Sir, Your obedient servant, TO BLUE AND GILD STEEL. MR. EDITOR,-In answer to your Correspondent, A. R., No. XVIII., I beg leave to observe, that the mode employed in blueing steel is merely to subject it to heat. The dark blue is produced at a temperature of 600°; the full blue at 560°; and the bright blue at 5500 Your Correspondent has, therefore, only to subject the steel to the requisite degree of temperature. He may also gild steel by the following process:-To a solution of muriate of gold add nearly as much sulphuric ether; the ether reduces on the gold to a metallic state and l keeps it in solution, while the musc riatic acid separates, deprived of not its gold, and forming a distinction into the ether, which speedily evastg fluid. Put the steel to be gilded 291 porates, depositing a coat of gold fi on the metal by dint of the attracË tion between them. After the steel has been immersed it should be dipped into cold water, and the sq burnisher should be applied, which #ol strengthens its adhesion. Figures, of flowers, and all kinds of pretty o ornaments and devices, may be drawn on the steel, by using the g ether with a fine brush or pen. I am, Sir, Your obedient servant, Richmond, July 13. 1 ORACULUS.Vig MR. BARLOW'S IMPROVE have a considerable influence both sophical Journal.) We have already, in No. XV., mentioned the reward bestowed on Mr Barlow for his valuable discovery, which seems to have given, for the first time, a sure and safe guide to the mariner over the path less deeps. We now mean to explain more particularly, in what that discovery consists; and our motive for doing this is to spread, as far as we can, a knowledge that is likely to save the lives and property of many most valuable fellow-citizens. In a maritime country like ours, which, though so greatly indebted to its commerce for its prosperity, has not yet half profited by its admirable situation, the smallest details on maritime subjects should be interesting to the people. We shall not therefore, we trust, be censured for giving a place in our pages to an account of a discovery, which must without the precautions pointed out by Mr. Barlow, the loss both of property and lives, in the event of shipwreck, may, in most cases, be fairly attributable to the owners. But those owners only can be held b responsible who are acquainted with Mr. Barlow's discovery; and t we may do something towards creating that responsibility. Mothers who have children, wives d who have husbands, children who have fathers, and all who have relatives and friends at sea, must be interested in whatever contributes to their safety. Sailors are so ha bituated to danger, that they are proverbially careless, and even think it unmanly to take precaut tions. Those to whom they are t dear must, therefore, do this foru them, and enforce on them the nese cessity of adopting a landsman's dra discovery; because, not being so $ bold as they are, he has sought out of the means of avoiding danger. |