Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/851

 PHOSPHORUS 815 PHOSPHORUS AXD PHOSPHATES. &quot; Phosphorus &quot; ((ws&amp;lt;/&amp;gt;opos, light -bringer) had currency in chemistry as a generic term for all substances which shine in the dark without burning, until the name came to be monopolized by a peculiar kind of &quot; phosphorus &quot; which was discovered, some time previous to 1678, by the German alchemist Brand of Hamburg. Brand, hoping to obtain thereby an essence for the &quot;ennobling&quot; of silver into gold, sub jected urine- solids to dry distillation. In lieu of the hoped-for essence he obtained as part of the distillate a wax-like, easily fusible solid which, besides being phos phorescent, readily caught fire, to burn with a dazzling light into a white solid acid. The new phosphorus natur ally excited universal interest ; but it was, and remained, only a rather costly chemical curiosity until Scheele, in 1771, starting from the discovery of Gahn that bone-ash is the lime-salt of a peculiar non-volatile acid, proved that this acid is identical with the one formed in the com bustion of phosphorus, and that the latter, being only &quot; phlogisticated &quot; bone-ash acid, can be obtained from it by distillation with charcoal at a high temperature. This method of Scheele s is used to the present day for the manufacture of phosphorus, and even the theoretical notion on which it rests is recognized as correct as far as it goes, anhydrous bone-ash acid being a compound of phosphorus with oxygen the formation of which involves the liberation of part of the energy (&quot;phlogiston&quot;) of each in the kinetic form of heat. That phosphorus is an elementary sub stance was originally a surmise, which, however, has been confirmed by all subsequent experiences. In compara tively recent times it was found that Brand s phosphorus is susceptible of passing (by mere loss of energy) into two allotropic modifications, known as &quot; red &quot; and &quot; metallic &quot; phosphorus respectively, so that the name &quot; phosphorus &quot; has again come to assume a generic meaning, being used for these three substances and the element as such conjointly. Manufacture. For the manufacture of ordinary phos phorus any kind of phosphate of lime might be used, and in fact mineral phosphates are used occasionally, though as a rule the bones of domestic animals are employed as a raw material. Such bones (apart from a large percent age of water and a small admixture of fats and other subsidiary organic components) consist essentially of two things, namely, (1) osseine a nitrogenous organic com pound, insoluble in water, but convertible by long treat ment with hot water into a solution of &quot;glue&quot; and (2) an infusible and incombustible part, the two being united together (perhaps chemically) into a cellular tissue. The following analysis of the humerus of an ox gives an idea of the constitution of the second part and its ratio to the whole. Phosphate of lime, P.&amp;gt;0 5 3CaO 61 &quot;4 Phosphate of magnesia, P.,0 5 3MgO 1 7 Carbonate of lime 8 6 717 Osseine. 28 3 100-0 The percentages, however, in bones generally are sub ject to great variation. When bones are heated to red ness in the absence of air the organic part is destroyed, and there remains ultimately a cellular tissue of bone- phosphate impregnated, so to speak, with finely -divided charcoal. This black residue, known as &quot;bone-black,&quot; is used largely for the decoloration of sugar- syrup, and, after having been exhausted in this direction, forms a cheap material for the manufacture of bone-ash and con sequently of phosphorus ; but, as a rule, the phosphorus- manufacturer makes his bone- ash direct from bones, by burning them in a furnace (constructed and wrought pretty much like a limekiln) between alternate layers of coal. The burned bones (which retain their original shape) are ground up into granules of about the size of lentils, and these are then placed in a wooden tank coated inside with lead, to be decomposed by means of about their own weight of chamber -acid, i.e., sulphuric acid containing about 60 per cent, of real H 2 SO 4. To accelerate the action the bone-meal is mixed with boiling water previous to the addition of acid, and steam may be passed into the magma when its temperature threatens to fall too low. The acid readily decomposes the carbonate of the bone- ash, and then acts, more slowly, on the phosphate, the process being completed in about twenty-four hours ; and the result, in regard to the latter, is that about two-thirds of the phosphate are decomposed into sulphate of lime (gypsum), which separates out as a precipitate, and phos phoric acid, which unites with the residual one-third of the phosphate and the water into a solution of superphos phate of lime To eliminate the gypsum the mass is diluted with water, allowed to settle, and the solution drawn off with lead syphons, then the residue is washed by decantation, and ultimately filtered off through a bed of straw contained in a cask with a perforated bottom. The spent heat of the distillation-furnace is utilized to concentrate the united liquors to about 1 45 specific gravity, when a remnant of gypsum separates out, which must be removed. The clari fied liquor is then mixed with about one -tenth of its weight of granulated charcoal, and the whole evaporated in an iron basin until the mass is sufficiently dry to be passed through a copper sieve and granulated. The granules are heated cautiously over a fire, to be dehydrated as far as possible without loss of phosphorus (as phosphuretted hydrogen) ; and the dry mass is then transferred to fire clay retorts either pear-shaped with bent-down necks, or cylinders, about 18 inches long and 4 inches in diameter, with straight necks arranged within a powerful furnace. The condensers are made of earthenware, and must be so arranged that loss of phosphorus by combustion is avoided as far as possible ; its condensation takes care of itself. One construction is to give the condenser the form of a bell-jar resting in a saucer containing water ; lateral orifices in the bell serve to couple every two bells into one, to unite each with its retort-neck, and to send the vapour (of phosphuretted hydrogen, carbonic oxide, and other poisonous gases) into a chimney, where they take fire spontaneously, and the products are carried away by the draught. While the condensers are being adjusted the fire is kindled and raised very slowly, but ultimately forced up to the highest temperature which the retorts can stand, and maintained at this pitch until the appearance of the flames of the escaping vapours proves the absence from them of phosphorus, free or combined. This takes from thirty -six to forty -eight hours. The reduction -process, though in reality very complex, is in its principal features easily understood. The acid-phosphate behaves as if it were a mere mixture of -| x P 2 O- + J x P 2 5 3CaO (bone-phos phate). The quasi-free acid (fP 2 O 5 ) is reduced by the charcoal with formation of carbonic oxide and phosphorus- vapour, one-third of the phosphorus remaining in its original form of bone-phosphate. The distillation of phosphorus is rather a dangerous operation, because the connecting pipes at the condensers are apt to get blocked up with frozen phosphorus, and consequently must be cleared from lime by copper or iron wires being pushed through them (at a certain risk to the operator). Another difficulty is that, although a retort may be quite whole in the ordinary sense, it may, and as a rule does, admit of the perspiration of phosphorus-vapour. To render retorts as nearly as possible impermeable to the