80 



THE POPULAR EDUCATOE. 



4, that of the preceding elements being 1. The great affinity 

 phosphorus exhibits for oxygen precludes the possibility of its 

 being found free in nature. It chiefly exists in combination 

 with lime, as phosphate of lime (calcium phosphate, Ca 3 2POJ, 

 which is found in bones, and in the seeds of plants. The origin 

 of calcium phosphate is traced to a constituent of some of the 

 granitic rocks the mineral apatite from the disintegration of 

 which the soil has become possessed of this necessary ingre- 

 dient of all seed-producing soils. 



Preparation. Bone earth which is obtained by calcining 

 bones is composed of | phosphate of lime and ^ carbonate of 

 lime ; this is treated with diluted sulphuric acid, and kept at 

 100C for twenty-four hours. By this means all the carbonate of 

 lime becomes sulphate, and the phosphate is deprived of two 

 molecules of lime, which are replaced by two of water. Thus 

 3CaOP a O. + 2H a SO t = 2(CaSOJ + Ca02H a OP.,O li . 



This last salt is called the superphosphate of lime. Being soluble 

 it is easily separated from the calcium sulphate. Evaporating 

 down the solution to a syrup, a quarter of its weight of charcoal 

 is added, and the whole transferred to an iron retort. The neck 

 of the retort dips into water. On applying heat, bubbles of 

 carbonic oxide escape, and phosphorus, as a yellow wax-like 

 substance, distils into the water, the reaction being thus ex- 

 pressed : 



3(CaO2H.,OP. ) O 5 ) + IOC = 10CO + GH^O + 3CaO P a O, + 4P. 



Properties. It is sold in sticks, which are clear and colourless 

 when the substance is new. Its specific gravity is T83. It 

 oxidises at all temperatures above 0C, emitting a faint " phos- 

 phorescent" light, giving off white fumes, which are phosphoric 

 acid(P 2 5 ). It melts at 45C, and boils at 290C. It is extremely 

 inflammable, and must be handled with the greatest care, as 

 much under water as possible. Carbonic disulphido dissolves it 

 readily : from this solution it can be obtained in crystals. When 

 heated in an atmosphere of H, or CO 2 , to a temperature of 

 240C, it assumes its "amorphous" condition, which is a 

 dark red powder. This is more easily made by melting the 

 phosphorus with a trace of iodine. In this condition it is not 

 nearly so inflammable, need not be kept under water, and is not 

 soluble in carbonic disulphide. 



Matches. The great use of phosphorus is in the manufacture 

 of lucifer matches. The ordinary ones are composed of a 

 mixture of phosphorus, potassium chlorate, glue, and red leadj 

 the stick is first dipped in parafin, and then into the above paste. 



Bryant and May's safety matches, which strike only on the 

 lid, are made of sulphide of antimony, potassium chlorate, and 

 powdered glass. The lid is smeared with red amorphous 

 phosphorus, and ignition only takes place when the potassium 

 chlorate and phosphorus are rubbed together. By using the 

 above mixture, it is found unnecessary to dip the stick in 

 parafin, as it will catch fire from the ignited composition. This 

 action of phosphorus and potassium chlorate may be shown by 

 powdering a few grains of the salt, adding a piece of red phos- 

 phorus about the size of a pea, then very carefully folding it 

 up in paper ; upon striking it a moderate blow with a stick, a 

 somewhat violent explosion will ensue. Phosphorus is poison- 

 ous ; it has a singular action on the jaw-bone, which decays away : 

 this is said not to be the case with the amorphous variety. 



Phosplwric Anhydride (symbol, P 2 O 5 ) is a white powder, formed 

 when phosphorus is burnt in oxygen, or dry air. It is very 

 deliquescent, combining with three atoms of water, forming 

 the hydrated acid (3H 2 OP 2 O S ), which may be considered as, two 

 molecules of H 3 PO 4 . 



PhospJwric Add. The anhydride is capable of forming three 

 acids, by taking three different proportions of water. Consider- 

 ing the water as a base, the acids are named 

 Monobasic = II^OP.^,.. 

 Bibasic = 2H,OP a O 5 . 



Tribasic = 3H 3 OP,,O 5 . 



Sometimes the first is called "metaphosphoric acid," and the 

 second <: pyrophosphoric acid," because it is got from the third 

 by heat. 



The Monobasic is obtained by evaporating dilute phosphoric 

 acid to a syrup, and subjecting this to a low red heat. 



The Tribasic is procured by boiling for twenty minutes a 

 solution in water of " glacial phosphoric acid." This latter is 

 formed when the hydrate (2H 2 P0 4 ) is exposed to a red heat in 

 a platinum dish. The tribasic acid may be got in a crystalline 



form by evaporating its solution. If, now, these crystals ba 

 melted by heat, and the temperature maintained for some time 

 at 212C, one atom of the basic water will be expelled, and the 

 bibasic acid remains. These three kinds may, when in solution, 

 be thus distinguished 



The monobasic is the only one which will precipitate a solution 

 of albumen. 



The bibasic gives a white precipitate with nitrate of silver. 



The tribasic a yellow precipitate with the same salt. 



By replacing the atoms of water in these acids by various 

 bases, corresponding salts may be obtained. Sometimes the 

 water atoms are replaced by different bases. Thus 



H,0 



is microcosmic salt, which is miich used with the blowpipe. 

 This process may be thus exhibited 



H-.cn 



H=0 VP a O 5 , 



HOj 



Now replace one of the II by its equivalent of Na, and another 

 by its equivalent (NH 4 ) ammonium, so that we have 



H) 



HVPO. 



H) 



Na 



PJwsplwrous Acid (P 2 3 ) is obtained by burr.ing phosphorus 

 in a limited supply of air. It is bibasic, forming phosphites. 

 When raised to a high heat it is resolved into phosphoric acid, 

 and the gas next to be considered. 



4P 2 3 + 3H 3 O = 3P 3 O 5 + 2PH,. 



Phosphurelted Hydrogen (PH 3 ). When a few pieces of phos- 

 phorus are heated in a strong solution of potash, bubbles of 

 this gas are emitted, which, as they rise from the water into 

 which the delivery tube is dipped, take fire. As the combustion 

 is simultaneous at all points of bubble, a ring of white vapour 

 of phosphoric acid is formed. This very beautiful experiment is 



arranged as in Fig. 48. The flask must be nearly full of the 

 solution. 



Phosphuretted hydrogen is not spontaneously inflammable 

 when pure, but this property is due to the presence of a minute 

 quantity of a liquid, whose composition is supposed to be PH 2 . 

 It is this gas which sets fire to the bubble of marsh gas, forming 

 the ignis fatuus. 



PJwsplwrous Chloride (PC1 3 ). Clear phosphorus burns with a 

 pale blue flame in dry chlorine, forming this compound. It is 

 capable of decomposing water and other oxides, the chlorine 

 combining with the hydrogen, or the metal and the phosphorus 

 forming a phosphite (H 3 PO 3 ). 



Phosphoric Chloride (PC1 S ) is produced by a further action of 

 chlorine on phosphorous chloride. With bromine two similar 

 compounds are formed; with iodine the beautiful crystalline 

 P 2 I 4 , and with sulphur three well characterised sulphides P.fi, 

 P 2 S 3 , P 2 S 6 are produced. 



