What is nitrogen iodide ? Iodine scales saturated with ammonia produce a dry powder, NI, or NHI,, which with the slightest touch gives up its nitrogen explosively. What is the composition of the atmosphere? It also contains variable quantities of― Aqueous vapor, depending on the temperature; Ammonia, traceable; Solid matter (cosmical and terrestrial dust); Carbonic dioxide, 3.7 to 6.2 volumes in 10,000 volumes of air. What is the weight of air? One litre of pure air at 0° C. and 760 mm. pressure weighs 1.29366 grams, or about 14.42 times as heavy as hydrogen. Is the air a mixture or a chemical compound? It is merely a mixture. This is proved as follows : 1st. The composition is not absolutely constant, as would be the case if it were a chemical compound; 2d. When air is absorbed by water, then expelled, the ratio of the nitrogen and oxygen is not the same as in the original air; 3d. Air produced by mixing proper quantities of oxygen and nitrogen is not attended by any chemical phenomena. How is the analysis of air made? Analysis of air is roughly made by passing a given quantity of it over red-hot copper in a combustion-tube and catching the residual gas in an exhaust vessel. The oxygen combining with metallic copper forms copper oxide. The increased weight of the copper in the tube shows the amount of oxygen in the air, and the weight of the residual gas, nitrogen, is readily ascertained. Another method to ascertain the ratio of oxygen and nitrogen is to pass a given volume of air through some liquid absorbent of oxygen, as pyrogallate of potash. The decrease in volume thus equals the volume of the oxygen, the balance being nitrogen. PHOSPHORUS. Give the origin of the word. Symbol P. Atomic weight 31. The word is derived from phos, light, and pherein, to bear. Phosphorus was discovered by Brandt, in Hamburg, in 1669. 5-C. & P. State its occurrence. In combination as phosphates it occurs in ancient unstratified rocks and modern lava. As a result of their disintegration it occurs in fertile soils, from which it passes into the organisms of plants and ultimately into the bodies of animals subsisting on vegetable life. The composition of human bones is nearly half calcium phosphate, which gives them firmness and inflexibility. The most important mineral is apatite, Ca(PO4)2+Ca(FCI). It is extensively used as the source of fertilizers. Phosphates of lead, copper, iron, manganese, aluminium, magnesium, and of the rarer elements also occur. How is phosphorus obtained? By treating calcium phosphate with sulphuric acid, a precipitate of calcium sulphate and a solution of acid calcium phosphate is obtained. This solution is evaporated to a syrupy consistency, after which carbon is added and the whole subjected to distillation. The phosphorus is reduced and distilled, being caught under water to prevent oxidation. State the physical properties of phosphorus. Ordinarily, it exists as a yellowish-white, waxy solid, with the odor of a burning match. Its specific gravity is 1.837. It melts at 44° C. and boils at 290° C., giving a vapor density of 62, which is double its atomic weight, showing that a phosphorus molecule is composed of 4 atoms. Exposed to air at a low temperature it oxidizes slowly, emitting a feeble light, whence its name. State its chemical properties. (1) Ordinary phosphorus is extremely poisonous. It oxidizes readily, and must therefore be kept under water. It is highly inflammable, and on this account is used in the manufacture of matches. Ignited in contact with the skin, its burns are deep and painful. It is insoluble in water, slightly soluble in olive oil and ether, but freely soluble in carbon disulphide, yielding a dangerous combustible substance. (2) Amorphous or allotropic.-When common phosphorus is heated to 240° C. in an atmosphere free from oxygen, it becomes converted into an extraordinary allotropic form, possessing special properties. It is an odorless, non-luminous, dark red, opaque powder, insoluble, and not poisonous, and has a specific gravity of 2.11. Heated to 260°, it reverts to the ordinary phosphorus. (3) Bemsen and Keiser have recently described another form, analogous to flowers of sulphur. It is produced by distilling common phosphorus in an atmosphere of hydrogen, which yields a white, flaky sub stance. (4) A black variety has also been described by Thénard. What are the important compounds of phosphorus ? They are oxides, acids, and salts. How is phosphorous trioxide produced? It is the product of slow oxidation of phosphorus, and is a white powder, soluble in water, forming phosphorous acid : = 2P+30, P20, +01; How is phosphorous pentoxide obtained? : It is produced when phosphorus is burned in an excess of air :— 2P2+50,=2P205. It is a white powder, absorbing water in varying proportions to produce acids : 5 6 PO+2H20=H1P2O,, P2O, H2OH,P,O,=2HPO3, meta-phosphoric acid; Give two other acids of phosphorus. Hypophosphorous acid, H,PO2; Phosphorous acid, H,PO. Give the graphic formula for hypophosphorous acid. H-O-P H OH. How is this acid prepared? Phosphorus boiled with a solution of lime or baryta yields calcium or barium hypophosphite and phosphuretted hydrogen :— 8P+3Ba(OH)2+6H2O=3Ba(PH2O2),+2PH2. The acid is obtained by heating this hypophosphite with sulphuric acid. Hypophosphorous acid is a strong oxidizing agent. It forms salts called hypophosphites, several of which are used medicinally. Although this acid has three hydrogen atoms (see graphic formula), only one is replaceable; therefore it is a monobasic acid. How is phosphorous acid obtained ? By adding phosphorous trichloride to water, the action produces phosphorous acid and hydrochloric acid : PCI,+3H2O= H,PO,+3HC1. What are its properties? It is a crystallizable solid, very deliquescent, rapidly absorbing oxygen and passing into phosphoric acid. Its salts are phosphites. Give the graphic formula for orthophosphoric acid. H-O H-O How is it prepared? It may be prepared by several methods : (1) By a solution of phosphorous pentoxide in water; PC15+4H20=5HCl + H2PO. What are the properties of H ̧PO̟? It is a very powerful acid, but not poisonous. The aqueous solution evaporated and crystallized gives prismatic crystals. Heated to 160° C., the solution is unchanged; heated to 213° C., it gives up a molecule of water and forms pyrophosphoric acid; heated to a red heat, it gives up another molecule of water and forms metaphosphoric acid. This orthophosphoric acid gives rise to all the natural phosphates. Other phosphates are artificially prepared. Give some of the phosphates. Orthophosphoric acid forms salts called orthophosphates, and on account of being tribasic (having three replaceable hydrogens), it produces three kinds of salts. With sodium in combination these salts are :— With sodium and ammonium a triple salt is produced, called sodiumammonium hydrogen phosphate, Na(NH)'HPO. It is of great importance in blowpipe analyses, and is known as salt of phosphorus" or microcosmic salt.' 66 How is pyrophosphoric acid obtained? By heating orthophosphoric acid. Heat also produces pyro-phosphates from the ortho-phosphates. Give the graphic formula for metaphosphoric acid. By heating orthophosphoric acid or pyrophosphoric acid to redness. It is extremely deliquescent, and requires to be kept in closely stoppered bottles. Heat separates a corresponding salt into ammonia, water, and sodium metaphosphate : Na(NH)HPO,+ heat = NH,+H2O+NaPO,. How may phosphuretted hydrogen (PH,) or phosphine be prepared? It results from boiling water-slaked lime and phosphorus: 6H2O+3Ca(OH)2+8P = 2PH, +зCaн ̧P2O1 This gives phosphine and calcium hypophosphite. It is also prepared by the action of calcium phosphide and water. What are the properties of phosphine? It is a colorless gas, having an odor of decayed fish. As usually prepared it is inflammable, on account of the presence of vapors of PH. When perfectly pure it is not inflammable. It is slightly soluble in water. Mention some other compounds of phosphorus. With chlorine it forms two compounds: the trichloride, PCI,, and the pentachloride, PCl5, of phosphorus; also an oxy-chloride of phosphorus, POCI. Phosphorus combines with iodine and bromine and gives six compounds with sulphur. ARSENIC. Symbol As. Atomic weight 75. How does arsenic occur? (a) Free, as mineral native arsenic. (b) Combined, as sulphides, As,S,, mineral realgar; AS2S3, 66 orpiment. Also as several arsenides, arsenates, and sulph-arsenides, the most im portant of which is arsenopyrite, FeAsS. |