Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/854

 818 PHOSPHORUS some 16 oz. of fragments of phosphide of calcium. Two small circular portions of the tor! and bottom respectively consist of soft metal (lead). These are pierced with an appended pricker before the apparatus goes overboard along with the buoy, to which it is attached by means of a cord. The water penetrates through the lower hole and the gas comes out through the upper and burns with a brilliant flame, which is from 9 to 18 inches high and lasts for about half an hour. A larger similar contrivance, intended to be accommodated within a bucket full of water on deck, serves as an inextinguishable night-signal to ships in distress. By the British Merchant Shipping Act, 1876, Viet, 21, every sea -going passenger-steamer and every emigrant-ship must be provided with arrangements for inextinguishable distress -lights and life-buoy lights. In the British navy a peculiar form of the phosphide of calcium light is used in connexion with torpedo-practice. P/iosphorits Bases. This is a generic name for organic bases which are related to phosphine (PH 3 ), as the &quot;compound ammonias&quot; are to NH 3. See CHEMISTRY, vol. v. p. 516 sq. ; also METHYL, vol. xvi. p. 197. Tri-etliyl phosphine P(C 2 H 5 ) 3, a colourless self-inflammable liquid, readily unites with bisulphide of carbon into a red crystal line compound, and consequently is available as a delicate reagent for the detection of the vapour of this compound in coal-gas. PHOSPHATES. &quot; Phosphates,&quot; in chemistry, is a generic term for the salts formed by the union of the acid-anhydride P.,0 5 with bases or water or both. As explained in CHEMISTRY (vol. v. pp. 517, 518) there are three classes of phosphates customarily distinguished by the prefixes ortlio, pyro, and meta. The last two nowhere occur in nature, and are hardly known to the arts ; hence in this article only the ortho- compounds will be noticed, and their specific prefix will be dropped except where it is needed for definiteness. Combined phosphoric acid is universally diffused throughout the three kingdoms of nature, and (it is perhaps as well to add) to the practical, if not absolute, exclusion of all other phosphorus compounds. All organic tissues and juices contain it : of animal matters bones and blood- solids, of vegetable the seeds of cereals, may be referred to as being exceptionally rich in phosphates. Of mineral phosphates the follow ing may be here referred to : pyro-morphite, 3(P 2 5 . 3PbO) + PbCl 2 , where the chlorine may be replaced partially by fluorine ; wavellite, 2(AU0 3 - p A) + A1 A 3H -0 + 9Ar l (tliis is a crystalline mineral ; an amorphous or massive phosphate of alumina, known as &quot;rotondo- mineral,&quot; occurs as a large deposit onaWest Indian island); vivianite, P 2 5 3FeO + 8H 2 0. All these and any others that might be named are rare minerals compared with apatite and its derivatives. Apatite. This exists in a variety of forms, but, as long as unde- composed, always answers the formula 3(P 2 5 .3C aO) + (CaX.,). In the fluor-apatites the X 2 is wholly F 2 (fluorine) ; in the chlor-apatites it stands for (Cl,, F).,, i.e., chlorine and fluorine coming up conjointly to two equivalents. See vol. xvi. p. 407. Phosphorites. Phosphorite is the name given to many impure forms of amorphous or massive apatite, modified more or less by disintegration. It occurs in massive, irregular, corroded-looking nodules embedded in limestone or other kinds of soft rock near Amberg (Bavaria), in Baden, Wurtemberg, the Weser hills, and in the Teutoburger &quot;Wald, and contains from 40 to 80 per cent, of phosphate and up to 3 per cent, of fluoride of calcium ; the phos phorite nodules in the sandstone of Kursk and Voronezh, the &quot;South Carolina phosphate,&quot; and the &quot;Lot phosphate&quot; belong to the same category. It is met with (U) in more or less extensive beds, as &quot;kidneys,&quot; as stalactites, or as a connective cement in breccias ; such phosphorite, of which large quantities are found in the Lahn valley, generally contains only from 25 to 60 per cent, of phosphate of lime, and includes large percentages of clay or mail, and more or less of the phosphates of iron and alumina. Another variety is (c) black phosphorite slate. A deposit contain ing 20 per cent, of P.AD 5 occurs in the Coal-measures of Horde (Westphalia), also in Wales; an earthy deposit is found in the &quot; braunkohle &quot; of Pilgramsreuth in the Fichtelgebirge. Phosphorite is also found (d) in veins, as a stone of very varying structure, generally intermixed with quartz, for instance at Logrosan in Estremadura (65 to 80 per cent, of phosphate and up to 14 per cent, of fluoride of calcium), also in the Silurian slate of the Dniester. Coprolites. According to Buckland, coprolites are derived from the excrements of extinct animals. They consist of highly impure phosphate of lime. All native phosphate of calcium being fluor- iferous, we need not wonder at the constant occurrence of traces of phosphates in the bones of vertebrate animals ; the wonder is that the fluorine in these amounts to only 005 per cent. 1 Preparation. For the preparation of phosphates the oxide P 2 5 affords a natural starting-point. This substance is produced when phosphorus burns in an abundant supply of oxygen or air. Appa ratus for the convenient execution of the process on a preparative scale are described in the handbooks of chemistry. Phosphoric anhydride forms a snow-white, loose, inodorous powder, which, i Some books (Nickles) quote as high percentages as 1 or 1-5, but these are based on erroneous analyses. when heated in a hard glass tube to redness, sublimes slowly. It is extremely hygroscopic. When thrown into water it hisses like a red-hot iron and passes into the meta-acid, most of which, in spite of its abundant solubility, separates out as a sticky precipitate, which is rather slow in dissolving. It is the most energetic of all dehydrating agents ; even sulphuric acid, when distilled with an excess of it, suffers dehydration, and passes into SO 3. The pre paration is liable to be contaminated with red phosphorus and phosphorous anhydride (P 2 3 ), also with &quot;white arsenic,&quot; because most commercial phosphorus, being made by means of ^t/rites- vitriol, is arseniferous. A freshly-prepared solution of the anhydride in water, being one of the meta-acid, coagulates albumen (as IINO :i does) and gives a white precipitate with nitrate of silver. But, when the solution is allowed to stand, the dissolved meta-acid gradually passes into pyro-acid (P._,0 5 2H 2 0), and this latter again gradually passes into ortho-acid (P 2 6 S 3H 2 O), the highest hydrate. At a boiling heat, especially if a little nitric acid be added, the whole of the dissolved P.,0, is converted into ortho-acid in the course of one or two hours. The solution then does not coagulate albumen ; it gives no precipitate with nitrate of silver unless the, mixture be neutralized with an alkali, when a yellow precipitate of the salt P.j0 5. 3 Ag.,0 comes down. The aqueous ortho-acid, when evaporated at temperatures not exceeding 160 C., and ultimately dried at this temperature, leaves its substance P L ,0 5 .3H 2 as a thick syrup, which, when left to itself in a dry atmosphere, slowly freezes into crystals. At 215 C. the ortho-acid loses one-third of its water and becomes pyro-acid ; at a red-heat it is reduced to a &quot;glass&quot; of meta-acid, P 2 O 5 H 2 0, which retains its water even at the highest temperatures. The substance known in pharmacy as &quot; acidnm phosphoricum glaciale &quot; is very impure meta-acid. Ortho-Phos2&amp;gt;horic Add, H 3 P0 4. The synthetical method de scribed in the last paragraph is not so easy in practice as it appears on paper ; hence it is generally preferred to prepare this substance by the oxidation of ordinary phosphorus with nitric acid. An acid of 1 2 specific gravity works best ; weaker acid acts too slowly ; if stronger it may act with dangerous violence. One part of phos phorus is placed in a large tubulated retort, connected with an ordinary globular receiver, and treated therein, at a carefully regu lated heat, with ten or twelve parts of the acid. When about half the acid has distilled over, it is poured back and the opera tion resumed and kept on until all the phosphorus is dissolved. The excess of nitric acid is then distilled over as far as conveniently possible and thus recovered. Towards the end of the distillation a fresh gas-evolution sets in through the conversion of previously produced phosphorous acid (H 3 P0 3 ) into phosphoric. The residual liquid in the retort is now poured out into a Berlin porcelain (or, what is better, a platinum) basin, and, if it still contains phosphor ous acid, fully oxidized by evaporation with occasional addition of strong nitric acid. Phosphorous acid, if present, is easily detected by the following tests: (1) its solution, when mixed with nitrate of silver and excess of ammonia, gives a black precipitate of metallic silver ; (2) when heated with a solution of corrosive sublimate, HgCL it produces a white precipitate of calomel, HgCl ; (3) when heated to boiling with excess of aqueous sulphurous acid it gives a precipitate of sulphur, or, if arsenious acid is present, of sulphide of arsenic. When the final oxidation is accomplished the acid needs only be freed of the remnant of nitric acid by repeated evaporation with water to be ready for use if arsenic be absent. As a rule, however, this impurity is present and must be removed by diluting the acid, passing in sulphuretted hydrogen first at 70 C., and then in the cold, and allowing to stand for twenty-four hours, when all the arsenic is converted into sulphide, which, after elimination of the excess of sulphuretted hydrogen by continued exposure to air at a gentle heat, is filtered off. In practice, as a rule, the filtrate is being concentrated to some predetermined specific gravity and preserved as aqueous phosphoric acid, which preparation is official, and used besides for the cleansing of metallic surfaces, in lithography, and for other purposes. The British pharmacopoeia prescribes for the official acid a strength corresponding to 10 per cent, of P 2 5. Hager has published a complete table showing the dependence of the specific gravity, taken at 17 5 C., on the strength of the acid. From it the following is extracted. Spec. Grav. Percentages of Spec. Grav. Percentages of 1-800 1-077 1-521 1-448 ] 383 1-325 PsO s. H 3 P0 4. 08-0 93-7 CO-0 82-7 50 68-9 4.VO 62-0 40-0 55-1 3.0-0 48&quot;2 1-271 1-218 1-1C9 1-122 1-079 1-037 P 2 5. H 3 P0 4.
 * &amp;gt;,o-o 41-3

2.1-0 34-4 20-0 27 -0 15-0 20-7 10-0 13-8 5-0 6-9 Aqueous phosphoric acid has all the properties of a decided acid, but, for a mineral acid, the exceptional qualities of an agreeably sour taste and of non- poison ousn ess. Phosphoric is the only mineral acid which might be used as a condiment in place of vinegar