Page:EB1911 - Volume 21.djvu/500

Rh found that it consisted of a continuous band without separate bright lines. The solar spectrum extends farther both towards the violet and the red ends, but is less intense in the green when equal luminosities are compared.

Many of the bacteria of putrefaction are phosphorescent, and the light emitted by dead fish or molluscs or Eesh is probably due in every case to the presence of these. Under the microscope, the individual bacteria appear as shining points of light. The phosphorescence of decaying wood is due to the presence of the mycelium of Agaricus melleus, and various other species of Agaricus have been found to be luminous. The great displays of phos horescence in sea-water are usually due to the presence of very large numbers of small luminous organisms, either protozoa or protophyta. Of these Noctiluca miliaris and species of Peridinium and Pyrocystis are the most frequent, the two former near land and the latter in mid-ocean.

In higher animals the phosphorescence tends to be limited to special parts of the body which may form elaborate and highly specialized luminous organs. Many coelenterates show the beginning of such localization; in medusae the whole surface may be luminous, but the light is brighter along the radial canals, in the ovaries, or in the marginal sense-organs. In Pennatulids each polyp has eight luminous bands on the outer surface of the digestive cavity. Some Chaetopods (Chaetopterus and Tomopteris) have luminous organs at the bases of the lateral processes the body. Pyrosoma, a colonial pelagic ascidian, is responsible for some of the most striking displays of phosphorescence in tropical seas; it has two small patches of cells at the base of each inhalent tube which on stimulation discharge light, and the luminosity has been observed to spread through the colony from the point of irritation.

Amongst the Crustacea, many pelagic Copepods are phosphorescent. W. Giesbrecht has shown that the light is produced by a fluid secreted by certain dermal glands. A similar fluid in other Copepods hardens to form a protective case, and it may be that the display of light is in such cases an accidental by-product. Glands in the labrum of the Ostracod Pyrocypris and on the maxillae of the Mysid Gnathophausia similarly produce a luminous secretion. In the Euphausiacea, on the other hand, phosphorescence is produced by elaborate luminous organs which are situated on the thoracic appendages and the abdomen, and which were at first believed to be ocular organs. The deep-sea Decapod Crustaceans belonging to many families are luminous. A. Alcock observed that in some of the deep-sea prawns a luminous secretion was discharged at the bases of the antennae, but in most cases the luminous organs are numerous eye-like structures on the limbs and body.

The rock-boring mollusc, Pholas, which Pliny knew to be phosphorescent, has luminous organs along the anterior border of the mantle, two small triangular patches at the entrance of the anterior siphon, and two long parallel cords within the siphon. The cells of these organs have peculiar, granulated contents. W. E. Hoyle, in his presidential address to the Zoological Section of the British Association in 1907, brought together observations on the occurrence of luminous organs in no less than thirty-three species of Cephalopods. In Heteroteuthis, Sepiola and Rossia the light is produced by the secretion of a glandular organ on the ventral side of the body behind the funnel. The secretion glows through the transparent wall with a greenish colour, but, at least in the case of Heteroteuthis, continues to glow after being e ected into the water. In most cases the luminous organs are non glandular and may be simple, or possess not only a generator but a reflector, lens and diaphragm. The different organs shine with different coloured li hts, and as the Cephalopods are for the most part inhabitants of the depths of the sea, it has been suggested that they serve as recognition marks.

Some centipedes (e.g. Geophilus electricus and G. phosphoreus) are luminous, and, if allowed to crawl over the hand, are stated to leave a luminous trail. Amongst insects, elaborate luminous organs are developed in several cases. The abdomen of a Ceylonese May-fly (Teleganodes) is luminous. The so-called New Zealand “glow-worm” is the larva of the fly Boletophila luminosa, and some gnats have been observed to be luminous, although the suggestion is that in their case disease is present and the light emanates from phosphorescent bacteria. An ant (Orya) and a poduran (Anuraphorus) are occasionally luminous. The so-called lantern flies are Homoptera allied to the Cicadas, and the supposed luminous organ is a huge projection of the front of the head, regarding the luminosity of which there is some doubt. The glow-worms and true fire-flies are beetles. Eggs, larvae and adults are in some cases luminous. The organs consist of a pale transparent superficial layer which gives the light, and a deeper layer which may act as a reflector. They are in close connexion with the tracheae and the light is produced by the oxidation of a substance formed under the influence of the nervous system, and probably some kind of organic fat In the females the phosphorescence is probably a sexual lure; in the males its function is unknown.

Phosphorescent organs known as photophores are characteristic structures in many of the deep-sea Teleostome fishes, and have been developed in widely different families (Stomiatidae, Scopelidae, Halosauridae and Anomalopidae), whilst numerous simple luminous organs have been detected in many species of Selachii. The number, distribution and complexity of the organs vary much in different fish. They are most frequent on the sides and ventral surface of the anterior part of the body and the head, and may extend to the tail. The simpler forms are generally arranged in rows, sometimes metamerically distributed, the more complex organs are larger and less numerous. In Opostomias micrionus there is a large organ on a median barbel hanging down from the chin, others below the eyes, and one on the elongated first ray of the pectoral fin. In Sternoptyx diaphana there is one on the lower jaw, and in many species one or two below the eyes. The luminous organs appear to be specialized skin lands which secrete a fluid that becomes luminous on slow oxidation. The essential part of the organ remains a collection of gland cells, but in the more complex types there are blood vessels and nerves, a protecting membrane, an iris-like diaphragm, a reflector and lens. As the distribution and probably the colour of the light varies with the species, these organs may serve as recognition marks. They may also attract prey, and from their association with the eyes in such a position as to send light downwards and forwards it is probable that in the higher types they are used by the fish actually as lanterns in the dark abysses of the sea.

PHOSPHORITE, in mineralogy, the name given to impure massive (q.v.; see also ).

PHOSPHORUS (Gr. , light,  , to bear), the name originally given to any substance which possessed the property of (q.v.), i.e. the power of shining in the dark, but now generally restricted to a non-metallic element, which was first known as Phosphorus mirabilis or igneus. This element is very widely distributed in nature in combination, but is never found free. In the mineral kingdom it is exceptionally abundant, forming large deposits of (q.v.). It is also necessary to animal and vegetable life (see ). It occurs in the urine, blood, tissues, and bones of animals, calcium phosphate forming about 58% of bones, which owe their rigidity to its presence.

The element appears to have been first obtained in 1669 by Brand of Hamburg; Krafft bought his secret and in 1677 exhibited specimens in England, where it created an immense sensation. Its preparation was assiduously sought for, and Kunckel in 1678 and Boyle in 1680 succeeded in obtaining it by the same process as was discovered by Brand, i.e. by evaporating urine to dryness and distilling the residue with sand. This method was generally adopted until 1775, when Scheele prepared it from bones, which had been shown by Gahn in 1769 to contain calcium phosphate. Scheele treated bone ash with nitric acid, precipitated the calcium as sulphate, filtered, evaporated and distilled the residue with charcoal. Nicolas and Pelletier improved the process by decomposing the bone-ash directly with sulphuric acid, whilst Fourcroy and Vauquelin introduced further economies. In modern practice decreased bones (see ), or bone-ash which has lost its virtue as a filtering medium, &c., or a mineral phosphate is treated with sufficient sulphuric acid to precipitate all the calcium, the calcium sulphate filtered off, and the filtrate concentrated, mixed with charcoal, coke or sawdust and dried in a muffle furnace. The product is then distilled from Stourbridge clay retorts, arranged in a galley furnace, previously heated to a red heat. The temperature is now raised to a white heat, and the product led by malleable iron pipes into condensing troughs containing water, when it condenses. The chemical reactions are as follows: the treatment of the calcium phosphate with the acid gives phosphoric acid, H3PO4, which at a red heat loses water to give metaphosphoric acid, HPO3; this at a white heat reacts with carbon to give hydrogen, carbon monoxide and phosphorus, thus: 2HPO3+6C=H2+6CO+P2.

Electrothermal processes are also employed. Calcium phosphate, mixed with sand and carbon, is fed into an electric furnace, provided with a closely fitting cover with an outlet leading to a condenser. At the temperature of the furnace the silica (sand) attacks the calcium phosphate, forming silicate, and setting free phosphorus pentoxide, which is attacked by the carbon, forming phosphorus and carbon monoxide. As phosphorus boils at 290° C. (554° F.), it is produced in the form of vapour, which, mingled with carbon monoxide, passes to the