violently (gun-cotton). Strong nitric acid is partially decomposed, and coloured yellow, by the rays of the sun. If you colour some water blue in a test-tube with one drop of solution of sulphate of indigo, and add to it on boiling one drop of nitric acid, the blue colour will disappear. This reaction often serves for the detection of nitric acid. Experiment 8.-The nitrates are easily decomposed. Having powdered some of the nitrate of lead, obtained in Experiment 3 or 4, throw it upon a red-hot coal; active combustion of the coal will ensue, at the expense of the nitrate, and globules of metallic lead will remain beyond. Nitric acid is monobasic; that is, it contains but one atom of hydrogen which can be replaced by metals. Its salts are called nitrates, and it must be remembered that they all contain the monad radical, NO. HNO, Nitric acid. KNO, Potassium nitrate. Bi""(NO3) Bismuth nitrate. The nitrates are less easily decomposed than the chlorates, but they resemble the latter salts in the readiness with which they part with their oxygen to combustibles. In consequence of this property, potassium nitrate is a constituent of some inflammable and explosive mixtures, such as gunpowder, fuses, coloured fires, &c. Nitrous Oxide, NO. 2 Experiment 1.-Cautiously heat the ammonium nitrate, made by Experiment 7 (page 156), in a Florence flask to which a gas delivery tube is connected. The salt will gradually melt and soon effervesce briskly, as a gas-nitrous oxide-is evolved. When the air has been expelled from the flask the issuing gas may be collected at the pneumatic trough, which must be filled with warm water instead of cold, as the gas is soluble in the latter. The change which occurs is simple. Heat decomposes ammonium nitrate NH.NO, entirely into water and nitrous oxide: NH,NO, = 2H2O+N2O. M Nitrous oxide is seen to be a colourless gas. It can, however, be condensed to the liquid state by great pressure. It is respirable in moderate quantity, and its effects when inhaled are peculiar. At first it produces a pleasurable kind of intoxication-whence its name of laughing gas; but after a time it causes complete insensibility to pain. It is now much used as a substitute for chloroform in minor surgical operations. Nitrous oxide is a good supporter of combustion, its power in this respect being little inferior to that of oxygen. The experiments which were performed with the latter gas may be repeated with nitrous oxide, with little difference in their results. Nitric Oxide, NO, or N2O2. Experiment 1.-Pour over a few scraps of copper, placed in a wide-mouthed bottle, a little water, and then add by degrees some nitric acid, until a brisk effervescence ensues. This effervescence is caused by the evolution of nitric oxide, which must be collected in a jar of white glass over the Fig. 60. pneumatic trough. Close the mouth of the jar under water; it seems to be empty, for the nitric oxide is colourless; but if the jar be opened, and air be carefully blown in, then the jar becomes filled from above downwards with yellowish-red vapours. The nitric oxide takes thereby from the air one atom of oxygen, and is converted into nitric peroxide. NO becomes NO2. On account of this property, it has an important application in the preparation of common sulphuric acid (page 148). The following is the somewhat complicated formula which describes the formation of nitric oxide: Nitric Acid. 8HNO,+3Cu = Copper Nitrate. 3Cu"(NO3)2+4H2O+2NO. The copper nitrate remains as a blue solution in the bottle, and it may be obtained in crystals by evaporation. Nitric oxide supports combustion, although not with the readiness of nitrous oxide. If a piece of phosphorus be ignited and plunged into nitric oxide while feebly burning, it will be extinguished, but if the phosphorus burns briskly when immersed in the gas the combustion proceeds with energy. Nitrous anhydride, N2O,, is a red gas, easily condensed to a blue liquid by cold. With water it forms the very unstable nitrous acid, HNO2. Nitric peroxide, NO2, or NO, is the red gas formed when nitric oxide comes in contact with excess of oxygen. It is absorbed by water and converted into a mixture of nitrous and nitric acids: 2NO2 + H2O = HNO2+ HNO3. PHOSPHORUS. Symbol, P = 31. Formula for vapour, P. Great care is required in experimenting with phosphorus that it does not take fire at an unseasonable moment, as it continues burning with the greatest violence, and might occasion dangerous wounds. It may catch fire even when lying upon blotting-paper, particularly in summer-time, or by the heat of the finger. Hence it must be kept, and also cut, under water. On being taken from the water, it should be held by a pair of forceps, or be stuck on the point of a knife. Prudence also would dictate to experiment with small quantities only at a time, and to have a vessel of water in readiness, in which it may be quenched in case it should catch fire. Phosphorus, like sulphur, melts, boils, evaporates, and burns, but far more easily and rapidly. In winter it is brittle, in summer flexible as wax. When pure and freshly prepared it is colourless, transparent, and amorphous (noncrystalline), but after a time it becomes yellow, and coated over with a white crust. Phosphorus is insoluble in water, but soluble in ether, carbon disulphide, and oils. Phosphorus is an exceedingly violent poison, and is, for this reason, frequently employed for the extirpation of rats and mice. The rat paste, as it is called (phosphorus dough), is composed of one drachm of phosphorus, 8 ounces of hot water, and 8 ounces of flour. Preparation of Phosphorus.-Phosphorus was formerly obtained from urine, but is now prepared from bone-ash. Bones consist chiefly of gelatin (or rather ossein) and calcium phosphate, Ca"3(PO4)2. When the bones are calcined the gelatin burns away and the phosphate remains. The ash is treated with sulphuric acid, which converts the greater part of the calcium into the insoluble calcium sulphate, CaSO4, while impure phosphoric acid remains in solution. This is dried with charcoal powder and intensely heated in a clay retort. The carbon takes oxygen from the acid, forming carbonic oxide gas, CO, which escapes with the hydrogen of the acid. The phosphorus also comes over as gas, but is condensed by passing through cold water. The changes which occur in the above processes are somewhat more complicated than the description, which is only intended as an approximation, would imply. Experiments with Phosphorus. Experiment 1.-Put into a small flask first a quarter of an ounce of ether, then a piece of phosphorus, of the size of a pea. Cork the flask and let it stand some days, frequently shaking it. Decant the liquid; it contains in solution about one grain of phosphorus, and will serve for the following experiments. Experiment 2.-Pour some drops of this solution upon the hand, and rub them quickly together; the ether will evaporate in a few moments, but the phosphorus will remain upon the hands in a state of minutest division. The more finely it is divided, so much the more easily does it combine with the oxygen of the air. During this combination it diffuses a white smoke and a faint light (it phosphoresces), causing the hands to shine in the dark; hence its name, phosphorus, from pôs, light, and pépw, to carry. It undergoes slow combustion and is converted into phosphorous anhydride, P2O,, which rapidly takes up water from the air and becomes phosphorous acid: P2O2+ 3H2O = 2H,PO3. Experiment 3.-Moisten a lump of sugar with the solution of phosphorus in ether and throw it into hot water. The surface of the water will glow prettily in a dark room. Experiment 4.-Instead of ether use a few drops of carbon disulphide to dissolve the phosphorus. This liquid takes up more phosphorus than ether does, and the solution is highly dangerous. It is the basis of the modern "Greek fire." Its inflammability may be observed in the following way: Experiment 5.-Pour some of the solution upon fine blotting-paper; the latter ignites spontaneously after the liquid has evaporated. The more minutely the phosphorus is divided, so much the more readily it begins to burn. Experiment 6.-Put a piece of phosphorus of the size of a pea on blotting-paper, and sprinkle over it some soot or pulverised charcoal; it melts after a while, and spontaneously inflames. The finely pulverised charcoal causes this combustion, owing to its porosity. It eagerly absorbs oxygen from the air, imparts it again to the phosphorus, and, being a bad conductor of heat, the cooling of the latter is prevented. Fig. 61. Phosphorus is also easily ignited by friction, and is, for this reason, employed in the manufacture of lucifer-matches. The combustible mass is prepared from hot mucilage, at 158° F. (70° C), to which small pieces of phosphorus are added, being thoroughly incorporated with it by constant rubbing till cold. But as the mass, by becoming hard on drying, prevents the access of air to the phosphorus, there must be added some substance rich in oxygen, as black oxide of manganese, nitre, or red-lead, from which the phosphorus can abstract the oxygen necessary for its ignition. 1 part of phosphorus, 4 of gum Arabic, 4 of water, 2 of nitre, and 2 of red-lead, form a good inflammable mass. A temperature of 149° F. (65° C.)-158° F. (70° C.) is requisite for kindling such matches; in this case the temperature is caused by friction. The coating of the match is thus broken and kindled, and the continued burning is now maintained by the oxygen of the air. Experiment 7.-Put a piece of phosphorus, of the size of a pea, into a wineglass, and pour hot water upon it until the glass is half filled; the phosphorus melts, but does not |