March io, 1892] 



NATURE 



447 



20° C.) the oxide rapidly resolidifies in a most beautiful manner, 

 large crystals shooting out in all directions until the whole is one 

 compact mass of interlacing crystals. When the liquid is heated 

 in a distillation flask previously filled with one of the indifferent 

 gases carbon dioxide or nitrogen, it soon commences to boil, and 

 the vapour condenses in the condensing tube and the unchanged 

 oxide runs down into the receiver placed to intercept it in the 

 form of liquid, which eventually condenses to the solid again. 

 Its boiling point is I73°'l C. 



The vapour of phosphorous oxide possesses a very character- 

 istic odour, which appears to be the same as that so noticeable 

 about a lucifer-match manufactory. Owing to its great volatility, 

 both the solid and the liquid are constantly vapourizing, even at 

 the ordinary temperature, and hence the odour is always strongly 

 marked in their neighbourhood. 



Phosphorous oxiile may also be obtained by spontaneous 

 evaporation in vacuo in beautiful large isolated crystals, 

 probably belonging to the mnnoclinic system, which are quite 

 colourless and transparent, and very highly refractive ; crystals 

 have frequently been obtained in this manner an inch in length 

 and broad and thick in proportion, showing numerous prism and 

 pyramid faces. Similar crystals are obtained when solutions of 

 the oxide in carbon bisulphide, chloroform, ether or benzene, 

 in which the substance readily dissolves, are evaporated out of 

 contact with the air. 



Instead of reacting with violence with water, as appears to 

 have been generally supposed, phosphorous oxide is com- 



these volatile crystals in larger quantity, and of separating them 

 entirely from the pentoxide, a method has at length been found 

 by which as much as twenty-eight grams of the pure oxide have 

 been obtained in an experiment of five hours' duration. 



Two sticks of phosphorus are cut into pieces about an inch 

 and a half long, and placed in a glass tube bent into the shape 

 shown at a in the figure, so as to retain the phosphorus when in 

 the melted condition. The tube should be of i^-inch bore, and 

 should be made from new soft glass tubing, which is quite hard 

 enough to stand the heat of burning phosphorus. The tube is 

 drawn out somewhat, but quite open, at the end where the air is 

 to be admitted, and at the other is narrowed slightly, so as to 

 fit into the condenser b, a tight joint being obtained by means of 

 a caoutchouc ring or a little bicycle cement. This condenser, b, 

 is intended to retain the phosphorus pentoxide and any free 

 phosphorus produced during the combustion, and is maintained 

 at such a temperature that the phosphorous oxide passes uncon- 

 densed through it. It is therefore constructed of brass instead 

 of glass, and is made double, that is, with an outer jacket also 

 of brass, so that the space between the two bra-^s tubes may be 

 filled with water of the required temperature. This water may 

 be run in by means of a funnel through a small vertical tube, d, 

 a second such tube, e, serving for the introduction of a thermo- 

 meter. The size of condenser found most convenient is 2 feet 

 in length, and the inner brass tube has a bore of 25 millimetres. 

 At the end of the condenser furthest from the phosphorus, a 

 plug of glass wool about half an inch long is inserted, the 



Apparatus employed for the preparation of phosphorous oxide 



paratively indifferent to that liquid, only dissolving with great 

 slowness. If a few drops of the liquefied oxide are dropped 

 into water of about the same temperature they at once fall to the 

 bottom of the tube, and the two liquids do not mix. If the 

 water is at the ordinary temperature the oxide solidifies as it falls 

 to the bottom. A few grams of the oxide, either liquid or solid, 

 req^uire several hours for complete solution. The solution con- 

 tains phosphorous acid. When phosphorous oxide is warmed 

 with water to a temperature just below 100°, a violent reaction 

 of an entirely different nature occurs ; spontaneously inflammable 

 phosphoretted hydrogen is evolved with a loud explosion, and 

 red phosphorus and phosphoric acid are largely formed. 



Preparation of Phosphorous Oxide, 

 It is quite a mistake to suppose that when phosphorus is 

 burnt in a combustion-tube in a sloiu current of air the 

 lower oxide, and not phosphorus pentoxide, is produced. 

 Scarcely a trace of phosphorous oxide is obtained under these cir- 

 cumstances, the white amorphous powder deposited being pent- 

 oxide. It is only when the current is at all rapid that phosphorous 

 oxide commences to be formed. Its advent is at once apparent, 

 as it crystallizes all along the upper portion of the horizontal 

 combustion- tube in beautiful feathery crystals, which at once 

 melt if the finger is laid upon the exterior of the tube, while 

 the pentoxide settles out along the bottom of the tube. After 

 several less successful attempts to devise a method of producing 



NO. II 67, VOL. 45] 



fibres being arranged transversely as much as possible ; such a 

 plug forms an excellent means of filtering off any pentoxide 

 which would otherwise escape into the phosphorous oxide con- 

 denser, especially after the first few minutes of the combustion, 

 when its meshes become loosely filled with porous pentoxide. 

 Directly into the end of the brass condenser fits tightly, by 

 means of a cork annulus, the large glass U-lube condenser, c, 

 in which the phosphorous oxide is condensed. The yield of 

 oxide appears to depend somewhat upon the shape and dimensions 

 of this condenser, that found most advantageous having the 

 shape shown in the diagram, a height of 35 centimetres from 

 the bottom of the bend, and an internal bore of 14 millimetres. 

 A short vertical tube is fused on at the bend, and passes down 

 into a bottle, into which the oxide may be melted at the end of 

 each combustion. The whole condenser is surrounded by a tall 

 wooden box, indicated by dotted lines in the figure, containing 

 pounded ice. To the end of the condenser is attached a wash- 

 bottle, /, containing sulphuric acid, which serves to prevent 

 access of moisture to the oxide condensed in the U-tube, and 

 also to measure the rate of the current of air drawn through the 

 apparatus by the water pump. 



In making a preparation, as soon as the phosphorus, diiei by 

 blotting-paper, has been introduced and the tube containing it 

 attached to the brass condenser, which at first is quite cold, the 

 phosphorus is warmed to the igniting point and the pump set 

 working by turning on the water-tap to which it is firmly 



