Obrázky na stránke


AE 11:52





PHO PHOSPHITES, are salts formed of the the water, from which it may be obtained phosphorous acid, with alkalies, earths, in a state of purity by evaporation. The &c. In several of their properties they specific gravity of this acid varies accordresemble the phosphates; but may be ing to the different states in which it exdistinguished from them, by appearing ists. In the liquid state it is 1.4; in the luminous when heated with the blow dry state it is 2.7 ; in the state of glass pipe, and by affording, by distillation, a 2.85. It changes the colour of vegetable small quantity of phosphorus. They de- blues to red; has no smell, but a very tonate, too, with oxy-muriate of potash, acid taste. When it is exposed to the and precipitate gold from its solution in air it attracts moisture, and is converted a metallic state. By exposure to the air, into a thick viscid Auid, like oil. It is very they pass into phosphates.

soluble in water. When in the form of PHOSPHORESCENCE,} See Light.

dry flakes, it dissolves in a small quantity

of this liquid, producing a hissing noise PHOSPHORIC acid. When phospho- like that of a red hot iron plunged into rus undergoes combustion in oxygen gas, water, with the extrication of a great a great quantity of white fumes are pro- quantity of heat. The component parts duced, which are deposited in white of this acid have been accurately asflakes. These are phosphoric acid; so certained by Lavoisier, and it consists that it is a compound of phosphorus and of, oxygen. The phosphoric acid was first shewn to be distinct from all other acids,


60 in the year 1743, by Margraaff. He found that it existed in the salts which were


40 taken from human urine, and that phos

100 phorus could only be obtained from this acid, as well as that it could be converted into phosphoric acid. This acid was found to exist in some vegetable sub It combines with the alkalies, earths, stances, although it was formerly suppos and metallic oxides, and forms salts which ed to be peculiar to animal matters. are denominated phosphates. Phosphoric acid may be obtained, not on PHOSPHORITE, in mineralogy, is of ly by the method just mentioned, but also a yellowish white, frequently spotted with by transmitting a current of oxygen gas grey: it occurs massive; internally it is through phosphorus melted under water. glistening, sometimes dull; it is transThe acid, as it is formed, combines with lucent on the edges, soft, brittle, and not

very heavy. It forms a great bed in the cret of the process for preparing it to the province of Estremadura in Spain. In Royal Society of London in 1680. It is appearance it resembles curved, lamellar, asserted, indeed, by Krafft, that he disheavy spar; but it is harder and lighter covered the secret to Mr. Boyle, having than this kind of heavy spar.

in the year 1678 carried a small piece of PHOSPHOROUS acid, is obtained by it to London, to show it to the royal famithe slow combustion of phosphorus at the ly: but there is little probability that a common temperature of the air. If phos man of such integrity as Mr. Boyle would phorus, in small pieces, be exposed to claim the discovery of the process as his the air in a glass funnel placed in a bot own, and communicate it to the Royal Sotle, it attracts the oxygen and moisture ciety, if this had been the case. Mr. from the atmosphere, and runs down in- Boyle communicated the process to Godto the bottle. This is the phosphorous frey Hankwitz, an apothecary of London, acid. By this process, about three times who for many years supplied Europe the weight of the phosphorus is obtain with phosphorus, and hence it went uned. It is then in the form of a thick li. der the name of English phosphorus. In quid, adhering to the sides of the vessel. the year 1774, the Swedish chemists, It varies in consistence according to the Gahn and Scheele, made the important state of the air. Its specific gravity is discovery, that phosphorus is contained not known. It has an acid pungent taste, in the bones of animals, and they improv. not different from phosphoric acid. It ed the processes for procuring it. also reddens vegetable blue colours. The The most convenient process for obphosphorous acid is not altered by light. taining phosphorus seems to be that reWhen exposed to heat in a retort, part commended by Fourcroy and Vauquelin, of the water combined with it is first which we shall transcribe. Take a quandriven off, and when it is concentrated, tity of burnt bones and reduce them to bubbles of air suddenly rise to the surface, powder. Put 100 parts of this powder and collect in the form of white smoke, into a porcelain or stone-ware basin, and and sometimes inflame, if there be any dilute it with four times its weight of waair in the apparatus. If the experiment ter. Forty parts of sulphuric acid are be made in an open vessel, each bubble then to be added in small portions, takof air, when it comes to the surface, pro- ing care to stir the mixture after the adduces a vivid deflagration, and diffuses dition of every portion. A violent efferthe odour of phosphorated hydrogen gas. vescence takes place, and a great quantiThis acid is composed of the same con ty of air is disengaged. Let the mixture stituent parts as the phosphoric, and is remain for twenty four hours, stirring it considered by some as the phosphoric occasionally, to expose every part of the acid holding in solution a small quantity powder to the action of the acid. The of phosphorus. Phosphorous acid forms burnt bones consist of the phosphoric compounds with alkalies, earths, and me. acid and lime ; but the sulphuric acid tallic oxides, which are known under the has a greater affinity for the lime than the name of phosphites.

phosphoric acid. The action of the sulPŇOSPHORUS. This singular sub- phuric acid uniting with the lime, and the stance was accidentally discovered in separation of the phosphoric acid, occa1677 by an alchymist of Hamburgh, nam sion the effervescence. The sulphuric ed Brandt, when he was engaged in acid and the lime combine together, besearching for the philosopher's stone. ing insoluble, and fall to the bottom.Kunkel, another chemist, who had seen Pour the whole mixture on a cloth filter, the new product, associated himself with so that the liquid part, which is to be reone of his friends, named Krafft, to pur- ceived in a porcelain vessel, may, pass chase the secret of its preparation ; but through. A white powder, which is the the latter, deceiving his friend, made the insoluble sulphate of lime, remains on the purchase for himself, and refused to com filter. After this has been repeatedly municate it. Kunkel, who at this time washed with water, it may be thrown knew nothing further of its preparation away; but the water is to be added to than that it was obtained by certain pro that part of the liquid which passed cesses from urine, undertook the task and through the filter. Take a solution of succeeded. It is on this account that the sugar of lead in water, and pour it gradusubstance long went under the name of ally into the liquid in the porcelain baKunkel's phosphorus. Mr. Boyle is also sin. A white powder falls to the bottom,

considered as one of the discoverers of and the sugar of lead must be added so - phosphorus. He communicated the se long as any precipitation takes place,

The whole is again to be poured upon a raised. When phosphorus is heated to filter, and the white powder which re the temperature of 148° it takes fire, mains is to be well washed and dried. burns with a bright flame, and gives out The dried powder is then to be mixed a great quantity of white smoke. Phoswith one-sixth of its weight of charcoal phorus enters into combination with oxypowder. Put this mixture into an earth gen, azote, hydrogen, and carbon. Phosen-ware retort, and place it in a sand bath, phorus is soluble in oils, and when thus with the beak plunged into a vessel of dissolved, forms what has been called liwater. Apply heat, and let it be gradu- quid phosphorus, which may be rubbed ally increased, till the retort becomes red on the face and hands without injury. It hot. As the heat increases, air-bubbles dissolves too in ether, and a very beautirush in abundance through the beak of ful experiment consists in pouring this the retort, some of which are inflamed phosphoric ether in small portions, and when they come in contact with the air at in a dark place, on the surface of hot wathe surface of the water. A substance ter. The phosphoric matches consist of at last drops out similar to melted wax, phosphorus extremely dry, minutely diwhich congeals under the water. This is vided, and perhaps a little oxygenized. phosphorus. To have it quite pure, The simplest mode of making them is to melt it in warm water, and strain it sever put a little phosphorus, dried by blotting al times through a piece of shammy lea. paper, into a small phial; heat the phial, ther under the surface of the water. To and when the phosphorus is melted turn mould it into sticks, take a glass funnel it round, so that the phosphorus may adwith a long tube, which must be stopped here to the sides. Cork the phial closely, with a cork. Fill it with water and put and it is prepared. On putting a common the phosphorus into it. Immerse the fun- sulphur match into the bottle, and stiring nel in boiling water, and when the phos- it about, the phosphorus will adhere to phorus is melted, and flows into the tube the match, and will take fire when of the funnel, then plunge it into cold brought out into the air. water, and when the phosphorus has be PHOSPHURETS, in chemistry, are come solid, remove the cork, and push substances formed by an union with phosthe phosphorus from the mould with a phorus; thus we have the phosphuret of piece of wood. Thus prepared, it must carbon, which is a compound of carbon be preserved in close vessels, containing with phosphorus: we have also the phospure water. When phosphorus is per- phuret of lime, hydrogen, &c. fectly pure, it is semi-transparent, and has PHOSPHURETTED hydrogen, phosthe consistence of wax. It is so soft that phorus dissolved in hydrogen gas; which it may be cut with a knife. Its specific may be done by introducing phosphorus gravity is from 1.77 to 2.03. It has an into a glass jar of hydrogen gas standing acrid and disagreeable taste, and over mercury, and then melting it by peculiar smell, somewhat resembling means of a burning glass ; the gas disgarlic.

solves a large proportion of it. The When a stick of phosphorus is broken, compound has a very fetid odour, someit exhibits some appearance of crystalliza- thing like that from putrid fish. When tion. The crystals are needle shaped, it comes into contact with common air, it or long octahedrons; but to obtain them burns with great rapidity, and if mixed in their most perfect state, the surface of with that air is detonates violently. Oxythe phosphorus, just when it becomes so gen gas produces a still more rapid and lid, should be pierced, that the internal brilliant combustion than common air. liquid phosphorus may flow out, and When bubbles of it are made to pass up leave a cavity for their formation. When through water, they explode in succesphosphorus is exposed to light, it be- sion as they reach the surface of the licomes of a reddish colour, which appears quid; a beautiful column of white smoke to be an incipient combustion. It is is formed. This gas is the most combustherefore necessary to preserve it in a tible substance known. Its combustion dark place. At the temperature of 990 is the combination of its phosphorus and it becomes liquid, and if air be entirely hydrogen with the oxygen of the atmosexcluded, it evaporates at 2190, and boils phere, and the products are phosphoric at 554o. At the temperature of 43° or acid and water. These substances, mix44°, it gives out a white smoke, and is ed or combined, constitute the white luminous in the dark. This is a slow smoke. combustion of the phosphorus, which be PHOTOMETER, an instrument intendcomes more rapid as the temperature is ed to indicate the different quantities of


[ocr errors]

light, as in a cloudy or bright day, or be- of such an instrument one might also com. tween bodies illuminated in different de pare the action of rays of light in difgrees. The ratio of the intensities of two ferent countries, of which some dari with luminous objects has been attempted to be sufficient constancy from a fine and serene measured by placing them at different dis- sky, while others seem to be covered tances from a given object, until that ob with a veil, which dims and obscures their ject cast two shadows of equal darkness; or lustre. Mr. Leslie, having proposed to by observing when two equal objects ap himself to measure the energy of the sepeared to be equally illuminated each by veral coloured rays which compose the one of the luminous objects : for then, by a solar spectrum, caused a beam of light to well known and established law, the pro pass through a prism of Aint glass; and portion of the intensities of their light was the indications of the photometer presentsupposed to be as the squares of the distan ed successively to the different parts of ces. Thus if two equal objects appear to the spectrum have furnished, nearly, for be equally illuminated, when one of them the relation between the degrees of force is three feet from a tallow candle,and when of the blue, green, yellow, and red rays, the other is nine feet from a wax candle, that of the numbers 1, 4, 9, 16; a relation then it is inferred that the intensity of the which, considered in the two extreme light of the former candle is to that of the terms, is more than quadruple that which latter as nine to eighty-one. Mr. Leslie has was substituted for it by Dr. Herschel, more recently invented an instrument of who has made experiments for the same this kind, the essential part of which con purpose. sists of a glass tube like a reversed syphon, PHRYGANEA, in natural history, a ge. whose two branches should be equal in nus of insects of the order of Neuroptera. height, and terminated by balls of equal Generic character: mouth with a horny diameter; one of the balls is of black short curved mandible ; feelers four; enamel, and the other of common glass, three stemmata ; antennæ setaceous, longinto which is put some liquid.

er than the thorax; wings equal, incumThe motions of the liquor, which is sul- bent, the lower ones folded. There are phuric acid tinged red with carmine, are nearly sixty species, in two divisions. A. measured by means of a graduation : the Tail with two truncate bristles. B. Tail zero is situated towards the top of the without bristles. The insects of this gebranch that is terminated by the enamel nus are seen in a summer's evening floatled ball. The use of this instrument is ing in the air in large masses, and are eafounded upon the principle, that when gerly devoured by swallows. They rethe light is absorbed by a body, it pro semble moths, particularly the division duces a heat proportional to the quantity called Tineæ ; but may readily be distinof absorption. When the instrument is guished by their feelers, and also by the exposed to the solar rays, those rays that stemmata situated at the top of the head. are absorbed by the dark colour, heat the The phryganeæ proceed from aquatic larinterior air, which causes the liquor to væ of a lengthened shape, residing in tudescend at first with rapidity in the cor bular cases, which they form by agglutiresponding branch. But as a part of the nating various fragments of vegetable subheat which had introduced itself by means stances, &c. These tubular of the absorption, is dissipated by the ra lined within by a tissue of silken fibres, diation, and as the difference between the and are open at each extremity. The inquantity of heat lost and that of the heat cluded larvæ, when feeding, protrude the acquired goes on diminishing, there will head and fore parts of the body, creeping be a point, where, these two quantities along the bottom of the waters they inhaving become equal, the instrument will habit, by means of six short and slender be stationary, and the intensity of the inci. legs; on the upper part of the back is a dent light is then estimated by the num sort of prop, preventing the case, or tube, ber of degrees which the liquor has run from slipping too far forwards during the over. The author of this ingenious instru- time the animal is feeding. One of the ment has pointed out its advantages in de- largest species is the P. grandis, (see termining the progressive augmentation Plate IV. Entomology, fig. 2). This inundergone by the intensity of the light, sect is about an inch in length, very like and the gradation in a contrary sense, a phalæna; the upper wings are grey, which succeeds to that progress, both marked by various darker and lighter from the beginning of day to its end, streaks and specks, and the under wings and from the winter solstice to the end of yellowish brown, and semi-transparent. the succeeding autumn. With the help The larvæ of this genus is known by the

cases are

« PredošláPokračovať »