PREPARATION OF GUNPOWDER. 433 must be evolved when powder is burned. But gunpowder burns rapidly and with great evolution of heat, so that the volume of gas, large at any temperature, is enormously expanded at the moment of its formation; hence it happens that the gas set free in the barrel of a gun may be capable of occupying a thousand or fifteen hundred times as much space as the powder which generated it. An enormous pressure is thus engendered at the spot where the powder burns, and to this pressure some part of the matter which confines the powder must yield. In the case of the gun-barrel, it is the bullet which represents the weakest, or breaking side of the chamber in which the powder burns; but when rocks are blasted, then the packing, or "tamping," which represents the ball, is made so firm that it shall be stronger than the rocky sides of the drill-hole, which is equivalent to the barrel of the gun. In case the walls of the gun can be disrupted more readily than the firmly impacted bullet can be driven out, then, of course, the gun bursts; and, conversely, the tamping of a drill-hole is thrown out if it be less firm than the rock. In the case of the gun-barrel, a part of the effect of the explosion is felt in the kick or recoil of the gun. Though the equation last given is useful in so far as it exhibits the gaseous products evolved during the combustion of gunpowder, it does not truly express the solid products of the reaction. The residue of the combustion really contains only a comparatively small proportion of sulphide of potassium; it consists mainly of sulphate of potassium and carbonate of potassium, together with some hyposulphite of potassium, and a trace of unburned carbon. Enough sulphide of potassium is always present, however, to impart the offensive odor which is perceived in washing a foul gun, and in powder-smoke. Exp. 254.-Pulverize, separately, 23 grms. of nitrate of potassium, 4 grms. of sulphur, and 4 grms. of charcoal. Place a drop or two of water in a porcelain mortar, and grind into it, first, the charcoal, and then the other ingredients, taking care to add enough water to form a plastic dough. After the mass has been thoroughly kneaded, roll out small portions of it between two pieces of board, into long threads, of the thickness of a fine knitting-needle. With a knife, cut the threads into small fragments or granules, and leave the granules in a warm room to dry. The thoroughly dried product is gunpowder; and the 434 CHLORATE OF POTASSIUM. manipulation in this experiment does not differ essentially from the mode of manufacture employed in the powder-mills, excepting that the granulation is there effected by passing the moist paste through cullenders. The sulphur in gunpowder acts mainly as a kindling material ($200). In powder intended for use in guns, the proportion of sulphur is kept comparatively low, since any excess of it would corrode the metal of the gun. Exp. 255.-Knead together, as in Exp. 254, 7 grms. of powdered nitrate of potassium and 1.5 grm. of moistened, finely powdered charcoal. Granulate and dry the product, as before, and compare its inflammability with that of the gunpowder prepared in Exp. 254, by touching small heaps of each with a red-hot wire. Mixtures of charcoal and nitrate of potassium, such as the foregoing, are much used in the manufacture of fireworks. 517. Chlorate of Potassium (KC10,).—The basis of the large use now made of this beautiful salt in medicine, in calico-printing, in pyrotechny, in the match-manufacture, and in the chemical laboratory is its large oxygen-contents. It is an oxidizing agent of the most vigorous description. It may be prepared by saturating a solution of 1 part of hydrate of potassium in 3 parts of water with chlorine, and heating the liquid some time to the boiling-point. The ultimate result may be expressed by the formula 6KHO+601 = KC10, + 5KCl + 3H2O; but the process has two stages, which are sufficiently described in § 124. The hot solution, left to itself, deposits the greater part of the chlorate in anhydrous six-sided plates of a pearly lustre; the chloride of potassium remains in the mother-liquor. The chlorate is freed from adhering chloride by recrystallization. The success of the process depends upon the very different solubilities of the chlorate and the chloride of potassium. At the temperature of their saturated boiling solutions both salts are about equally soluble; 100 parts of water will dissolve between 60 and 67 parts of either salt; but at the ordinary temperature of the air 100 parts of water will dissolve 30-40 parts of chloride of potassium and only 6 or 7 parts of chlorate of potassium. We find here the explanation of the fact that chlorate of sodium has not replaced chlorate of potassium in the arts. The chlorate of sodium is more soluble in water at all temperatures than the chloride of sodium is, while both are exceedingly soluble, so that the two salts cannot be separated by crystallization. This process of crystallization is the chemical manufacturer's chief reliance in refining both his materials PREPARATION OF CHLORATE OF POTASSIUM. 435 and his products; and the purchaser of chemicals finds his best guaranty of the purity of his commodities in the peculiar form, lustre, color, and degree of transparency which characterize the crystals of every crystallizable and permanent chemical compound. Hence an easily crystallized permanent salt, of characteristic appearance, like chlorate of potassium, will always have the preference over one which, like chlorate of sodium, can be crystallized and purified only with difficulty, and is not permanent when once obtained. The chlorate of sodium is deliquescent. The waste product in the making of chlorate of potassium by the process just described is chloride of potassium, a comparatively dear salt. An economy is effected by substituting hydrate of calcium for hydrate of potassium, and thus making the secondary product chloride of calcium instead of chloride of potassium; one equivalent only of the chloride of potassium is then required instead of six of the hydrate of potassium. An excess of chlorine is passed into a mixture of 300 parts of quicklime, 154 parts of chloride of potassium, and 100 of water. The mass is heated by steam, stirred with agitators, filtered, and then evaporated nearly to dryness by steam-heat; the mass is then redissolved in hot water and set to crystallize :— 3CaO+ KCl + 6C1 = KCIO, 3CaCl2. The mother-liquor, which contains all the chloride of calcium, may be decomposed with sulphate of potassium, in which event a very finely divided sulphate of calcium, available for "stuffing" in the manufacture of paper, is precipitated, and chloride of potassium is recovered, to be again applied to the production of the chlorate; or the chlorideof-calcium solution may be decomposed with carbonate of sodium, in order to precipitate a very finely divided carbonate of calcium, which is largely employed by the pharmaceutist and perfumer. In the latter case, chloride of sodium has to be thrown away. The whole manufacture is a good example of a technical chemical process. 518. Chlorate of potassium is easily decomposed by heat; at a moderate temperature it yields perchlorate and chloride of potassium (§ 124); but at a red heat it is resolved into chloride of potassium and oxygen (Exp. 7):-KC10,= KCl+30. Chlorate of potassium is so prompt an oxidizing agent that mixtures of it with combustible bodies often detonate violently when struck or heated (Exps. 113, 157). These combustions are dangerous unless very small quantities be used. It has been often proposed to replace gunpowder by such mixtures; a mixture of the chlorate with catechu, or some similar stable substance rich in tannin, is 436 OXIDATION BY CHLORATE OF POTASSIUM. the most promising of these suggestions. Strong acids, like sulphuric, nitric, and chlorhydric acids, decompose chlorate of potassium with evolution of oxides of chlorine, or of chlorine and oxygen. The decomposition is often attended with decrepitation, and sometimes with a flashing light; combustibles, like sulphur, phosphorus, sugar, and resin, are inflamed by the gases evolved. A mixture of chlorate of potassium and chlorhydric acid is used in toxicological investigations as an oxidizing agent for the destruction of organic matter (§ 329). The following formula will elucidate some of these reactions: = 3KC10, +2H,S0, 2010, + KC10 + 2KHSO + H2O 8KC10, + 6HNO, = 6KNO, + 2KC10, + 6C1 + 130 + 3H ̧0 4KCIO, + 12HCI = 4KC1 + 30102 + 9C1 + 6H2O. Exp. 256.-Pour into a conical test-glass 25-30 c. c. of water, and throw into the water some scraps of phosphorus, weighing together not more than 0.3 grm., and 3-4 grms. of crystals of chlorate of potassium. By means of a thistle-tube bring 5 or 6 c. c. of strong sulphuric acid into immediate contact with the chlorate at the bottom of the glass. Then withdraw the thistle-tube. In a moment the phosphorus is kindled, and burns with vivid flashes of light beneath the water. An evolution of chlorine accompanies the reaction. Exp. 257.-Rub 4 or 5 grms. of clean chlorate of potassium, free from dust, to a fine powder in a porcelain mortar. In powdering chlorate of potassium, care must be taken that the mortar and pestle are perfectly clean, and the salt free from organic matter, and that violent percussion and heavy pressure upon the contents of the mortar be wholly avoided. Place the powdered chlorate on a piece of paper, add an equal bulk of dry powdered sugar to the pile, and, with the fingers and a piece of card, mix the two materials thoroughly together. Mixtures of chlorate of potassium and organic matter are liable to explode, if strongly rubbed or but lightly struck. Wrap the mixture in a paper cylinder, and place the cylinder on a brick in a strong draught of air; let fall upon the mixture a drop of sulphuric acid from the end of a glass rod; a very vivid combustion will ensue, with the violet-colored flame characteristic of potassium. Exp. 258.-Mix together, on paper, with the precautions above described, 1 grm. of black oxide of copper, 1 grin. of sulphur, and 2.5 grms. of powdered chlorate of potassium. Place the mixture, inclosed in a paper cylinder, on the top of a brick, and touch it with a hot wire; it will burn vividly, and with a purple color which is prized in pyrotechny. AMMONIUM-SALTS. CHAPTER XXV. 437 AMMONIUM-SALTS. 519. The hypothetical metal ammonium (NH) is a device for explaining the constitution and properties of one well-defined class out of the several classes of compounds into which the gas ammonia enters. This class of compounds is that which results from neutralizing an aqueous solution of ammonia with acids, as in the following reactions: NH,H,O + HSO NH,HO + HNO = (NH)HSO + HO. = (NH,)NO, + H,O. Nitrate of Ammonium. According to this hypothesis, the crystalline salts which result from such neutralizations contain a group of atoms (NH) which is analogous in its action to potassium and sodium, and which forms salts analogous in composition to the potassium-salts. Thus chloride of ammonium (NH)Cl is analogous to chloride of potassium KC1; sulphate of ammonium (NH),SO, is analogous to sulphate of potassium K2SO,, and so forth (§ 91). All the actual evidence we possess of the separate existence and metallic character of the group NH, is contained in the following curious but inconclusive experiment: Exp. 259. Pour 8 or 10 c. c. of mercury into a small flask, and warm the mercury over a gas-lamp; drop upon the mercury six or eight bits of metallic sodium, no one of them larger than a hemp-seed. The sodium dissolves with some spattering in the warm mercury, and a sodium amalgam is thus obtained. Transfer the amalgam to a tall glass or bottle of at least 300 c. c. capacity, and pour over it a concentrated solution of chloride of ammonium. The amalgam immediately begins to swell up, and ultimately increases to 8 or 10 times its original bulk, in the cold, or to 20 or 30 times if the solution be hot, assuming a pasty consistency like that of soft butter, but preserving its metallic lustre. It begins to undergo spontaneous decomposition as soon as it is formed, and if it is placed in water, this decomposition is quite rapid; |