Phosphates. Action of carbou. Carbonates. Action of Bo ron. Action of me other. less so. They are mostly crystallizable, and totally or partially decomposable at a high temperature. The greater number of the phos phurets have only been examined by Pelletier, Annales de Chimie, Tom i. et xiii. and Mémoires et Observations de Chimie. 530. The metallic phosphates may be formed either by dissolving the oxides in phosphoric acid, or by adding a solution of phosphoric acid, or of an alcaline phosphate, to solutions of those metals which form insoluble or difficultly soluble phosphates. The greater number of the phosphates are decomposed by ignition with charcoal; and those containing volatile oxides are volatilized at high temperatures. In the neutral phospates the quantity of oxygen in the acid is to that in the base as 2 to 1. Thus phosphate of soda consists of 32 soda containing 8 oxygen, and 28 phosphoric acid containing 16 of oxygen. 531. When phosphorus is introduced into the solutions of those meta's which have but a feeble attraction for oxygen, it reduces them to the metallic state. Thus gold, silver, and platinum are thrown down by immersing a stick of phosphorus into their respective solutions. 532. Action of Carbon. Carbon unites to very few of the metals, and of the metallic carburets, one only is of importance, namely carburet of iron, or steel. 533. Carbonic acid unites with the greater number of the metallic oxides and forms Carbonates, of which the distinctive characters have already been noticed; many of them are of difficult solubility, and may be formed by adding an alcaline carbonate to the metallic solution. "Of the carbonates some are entirely, and others only partially decomposed at a red heat. Carbonate of magnesia, for instance, loses the whole of its carbonic acid at a red heat; carbonate of potassa retains it; and bi-carbonate of potassa loses one-half and passes into the state of carbonate. 534. The action of Boron upon the metals has not been investigated, though it appears from the experiments of Descotils, (Recherches Physico-chymiques de M. M. GAY-LUSSAC et THENARD) to be capable of uniting to platinum and iron. These compounds may be called borurets. The metallic borates are numerous but mostly unimportant. Many of them are insoluble and easily formed by adding solution of boracic acid, or a soluble borate to the metallic solution. 535. Action of the Metals upon each other. The metals may for the falstopon each most part be combined with each other, forming a very important class of compounds, the metallic alloys. Various processes are adopted in the formation of alloys depending upon the nature of the metals. Many are prepared by simply fusing the two metals in a covered crucible; but if there be a considerable difference in the specific gravity of the metals, the heavier will often subside, and the lower part of the bar or ingot, will differ in composition from the upper; this may be prevented by agitating the alloy till it solidifies. Mr. Hatchett found that when an alloy of gold and copper was cast into bars, the mould being placed perpendicularly, the upper part of the bar contained more copper than the lower.-Phil. Trans. 1803. Where one of the metals is very volatile, it should generally be added to the other after its fusion; and if both metals be volatile, they may be sometimes united by distilling them together. It has been a question whether alloys are to be considered as com pounds, or as mere mixtures; but their properties leave little doubt of their being real compounds, and in some cases they are found to unite in definite proportions only; and it is probable that all the alloys contain a definite compound of the two metals. 536. The principal characters of the alloys are the following: i. We observe a change in the ductility, malleability, hardness, and colour. Characters of Malleability and ductility, are usually impaired, and often in allora a remarkable degree: thus gold and lead, and gold and tin, form a brittle alloy. The alloy of copper and gold is harder than either of its component parts; and a minute quantity of arsenic added to copper, renders it white. ii. The specific gravity of an alloy is rarely the mean of its component parts, in some cases an increase, in others a diminution of density having taken place, as shown by the following Table from Thenard.Traité de Chimie, Vol. i. p. 394. Alleys possessed of greater specific gravity than Alloys having a specific gravity inferior to the the mean of their components. mean of their components. . The fusibility of an alloy is generally greater than that of its components. Thus platinum, which is infusible in our common furbaces, forms, when combined with arsenic, a very fusible alloy; and an alloy of certain proportions of lead, tin, and bismuth is fusible at $120, a temperature several degrees below the melting point of its Rost fusible constituent. iv. Alloys are generally more oxidizable than their constituents taken singly; a property which is, perhaps, partly referable to the formation of an electrical combination. Where an alloy consists of (wo metals, the one easily and the other difficultly oxidizable, it may be decomposed by exposing it to the action of heat and air, the former metal being converted into an oxide; its last portions, however, are often not easily separated, being protected by combination with the least oxidable metal. An alloy of three parts of lead and one of tin 18 infinitely more oxidizable than either of its components, and easily burns at a dull red heat. Specific gravity of alloys compared with their constitu ents. on 1. The action of acids on alloys may generally be anticipated by a knowledge of their effects upon the constituent metals; but if a solu-Action le metal be alloyed with an insoluble one, the former is often protect-loys. ed by the latter from the action of an acid. Thus, silver alloyed with L A 1. new metals the first seven produce alcaline oxides which ar reduction; and they rapidly decompose water at al character which announces their powerful attraction the next five decompose water when their temperature i theten following do not decompose water at a re the next five, which produce acids by uniting to oxygen As these twenty-seven metals are not reducible by hea some of them, when heated, give out a portion of oxy we metals which next follow, osmium excepted, have treble attraction for oxygen; and when their oxides ar they are reduced to the metallic state. The last six metals ar list from analogy; they are only known in the state o which have not hitherto been reduced. SECTION I. Potassium. 538. THIS metal was discovered in 1807 by Sir Humphry Davy,(Philos. Trans. 1808). He obtained it by submitting caustic potassa, or petash, to the action of Voltaic electricity: the metal was slowly evolved at the negative pole. By this process, however, it could only be procured in very minute quantities; and various other methods have been devised, of which the best is that described by Gay-Lussaç and Thenard. (Recherches Physico-chymiques.) It is as follows : 539. A sound and perfectly clean gun-barrel is bent, as shown in the annexed sketch. It is then covered with an infusible lute between the the letters o and E (fig. 1.) and the interior of the luted part is filled with clean iron turnings. Pieces of fused potassa are then loosely placed in the barrel between E and c. A A is a copper tube and small receiver, which are adapted to the extremity o, and to each other by grind This apparatus is next transferred to the furnace, arranged as shown in fig. 2, x and y representing two glass tubes dipping into merCury. The furnace is supplied with air by a good double bellows entering at B, and a small wire basket G, is suspended below the space E C. The part of the barrel in the furnace is now cautiously raised to a white heat, and the escape of air by the tube x shews that all is tight. Some burning charcoal is then put at the end E, of the cage G, which causes a portion of potassa to liquefy and fall into the low part of the barrel upon the iron. Hydrogen gas instantly escapes by the tube x, and attention must now be had to keep the copper tubes A A cool, by aying wet cloths upon them. When the evolution of gas ceases, fresh Charcoal is placed under the potassa, and so on till the whole has passed down; if too much potassa be suffered to fall at once, the extrication fgas at x will be very violent, which should be avoided. If the space between a and o should become stopped by potassium, gas will issue by tuber (which must always be under a greater pressure of quick Character. with oxygen. silver than the tube x), and it may be fused by applying hot charcoal to the tube, when the gas will again appear at x and cease at T. When the operation is concluded, the tubes x and y are removed, and corks quickly applied to the holes; and when the apparatus is cool, the barrel is carefully removed from the furnace, and a little naphtha suffered to run through it. The potassium is found in globules in the tube and receiver a a, and considerable portions often lodge at o. The success of this operation is certain, if the heat has been sufficient; but the barrel, if not very carefully covered with lute, is apt to melt, and much, if not the whole of the product is lost. 540. Potassium is a white metal of great lustre. It instantly tarnishes by exposure to air. It is ductile, and of the consistency of soft wax. Its specific gravity is 0.85. At 150° it enters into perfect fusion; and at a bright red heat rises in vapour. At 32o it is a hard and brittle solid. If heated in air it burns with a brilliant white flame. It is an excellent conductor of electricity and of heat. 541. Potassium and Oxygen. When potassium is thrown into water Combination it instantly takes fire; hydrogen gas is evolved, and oxide of potassium or potassa, is found dissolved in the water. The quantity of hydrogen evolved in this experiment becomes the indicator of the proportion of oxygen which has been transferred to the metal; 100 parts of potassium are thus found to absorb 20 of oxygen; and if this be considered a protoxide, then 20:100::8:40,- so that 40 will be the number representing potassium, and 40 P. + 8 0. = 48 will represent dry oxide of potassium. Peroxide. Mode of pro Potassa. 542. Potassa, in the state it is usually met with in laboratories, contains a considerable portion of water, from which it may be freed by the action of iron at high temperatures, and there always remains in the barrel, after the above experiment, a large portion of dry potassa. It is a hard grey substance, which, by water, is slowly converted into the hydrated oxide, or caustic potash, which may be obtained by evaporation. This substance, after exposure to a red heat, is white and very soluble in water; it may be considered as a compound of 1 proportional of protoxide of potassium = 48+1 proportional of water 9 and its number = 57. 543. Peroxide of Potassium. - If the metal be heated in considerable excess of oxygen, it burns with intense heat and light, and an orange-coloured substance is obtained, which consists of 40 potassium+24 oxygen=64. This peroxide of potassium, when put into water, effervesces, oxygen is given off, and a solution of the hydrated protoxide is obtained. Peroxide of potassium is also formed by passing oxygen over potassa heated to redness. 544. The hydrated protoxide or caustic potash, is procured in our puting caustic laboratories by decomposing its carbonate by lime. The best process consists in boiling in a clean iron vessel, carbonate of potassa, (obtained by calcining tartar) with half its weight of pure quick lime, in water. The ley is strained through clean linen, concentrated by evaporation, again strained, and set by in a well-stopped bottle till it admits of being decanted clear from the sediment. The clear solution is to be evaporated to dryness. It is often cast into sticks for the use of surgeons, who employ it as a caustic, and in this state it generally contains some peroxide, and therefore evolves oxygen when dissolved in water. is the potassa fusa of the London Pharmacopeia. It may be further |