PHOSPHORIC ACID. 493 



(c.) This combustion is elegantly performed in a glass* globe, of 

 the capacity of three gallons, with a mouth two or three inches wide ; 

 a concave copper dish supported by wires which are hooked at the 

 top so as to hang from the orifice, contains the phosphorus ; a piece 

 not larger than a hazle nut should be employed ; the dry globe is 

 filled with oxygen gas flowing from a gazometer and introduced by 

 a tube going to the bottom and displacing the common air. 



A hot iron kindles the phosphorus, and a saucer is laid over the 

 orifice ; when one piece of phosphorus is burnt out, another may be 

 introduced through a glass tube, and will kindle of its own accord, 

 and so on till the oxygen is exhausted. 



This experiment, in one case, yielded me distinct crystals of perfectly 

 transparent phosphoric acid, scattered in great numbers in the interior 

 of the glass globe ; they were not larger than a pin's head, and were 

 formed from the viscous fluid arising from the deliquescence of flakes 

 of concrete, snow-white phosphoric acid ; when the air is admitted, it 

 deliquesces in a few minutes. 



(c?.) The above experiment is neatly performed by commencing 

 the combustion in a glass globe in common air or in oxygen gas, and 

 allowing the last to flow in as it is needed, from a gazometer through 

 a flexible tube ; by introducing phosphorus and oxygen gas, alter- 

 nately, the experiment may be safely continued as long as we please. 



(e.) Melt phosphorus in a thin glass globe underwater, and inject 

 oxygen gus through a tube, descending to the bottom of the vessel, 

 and connected with a bladder or gazometer ; as the gas, by small 

 portions at a time, comes in contact with the melted phosphorus, the 

 latter flashes beautifully under the water, which dissolves the acid 

 thus formed, and by evaporation, it is obtained solid.f Pelletier. 



(/.) Drop successively, small pieces of phosphorus into warm nitric 

 acid,$ diluted with an equal bulk of water, contained in a flask, or 

 tubulated retort. When the red fumes of nitrous acid gas cease, 

 and the fresh pieces of phosphorus readily take fire at the surface, 

 the process is through. 



By continuing the heat, any remaining acid will be expelled, and 

 the concrete phosphoric acid obtained ; 1 dr. 3 grs. of phosphorus, 



* See Lavoisier's Elements, and Dr. Hare's Compendium, p. 103, for an appa- 

 ratus admitting of accuracy, in consequence of the use of the air pump. 



t A considerable quantity of a red flaky substance floats in the water, which some 

 have regarded as an oxide of phosphorus. 



t If the acid be concentrated, there will be a rapid inflammation, and if the pieces 

 of phosphorus are large, there may be even a dangerous explosion. 



Some writers recommend concentrated acid in a platinum capsule: this will ordi- 

 narily induce inflammation, or explosion, with some danger and considerable loss ; 

 with a diluted acid, in a mattrass, both inconveniences may be avoided. I have 

 often tried both. 



