76 Prof. T. E. Thorpe on the Glow of Phosphorus. [Mar. 14, 



increases both in area and intensity, until at a certain temperature the 

 mass ignites. The change from glow to actual flame is perfectly 

 regular and gradual, and is unattended with any sudden increase in 

 brilliancy. In this respect the process of oxidation is analogous to 

 the sIjw and barely visible burning of fire-damp which is sometimes 

 seen to occur in the Davy lamp, or to the slow combustion of ether 

 and other vapours which has been specially studied by Dr. Perkin. 

 Other instances of what may be called degraded combustion are known 

 to chemists. Thrown into warm oxygen the substance bursts into 

 flame at once, and burns brilliantly ; and it also takes fire in contact with 

 chlorine. Alcohol also ignites it, and when it is warmed with water 

 or a solution of potash it evolves spontaneously inflammable phospho- 

 retted hydrogen. In contact with cold water it suffers only a very 

 gradual change, and many days may elapse before even a comparatively 

 small quantity is dissolved. This substance has long been known ; it 

 was discovered, in fact, by the French chemist, Sage, but its true 

 nature has only now been determined ; its chemical formula is found 

 to be P4O6 ; hence its composition is similar to that of its chemical 

 analogue arsenious oxide. 



The study of the properties of this remarkable substance enables 

 us to gain a clearer insight into the nature of the chemical change 

 attending the glow of phosphorus. When phosphorus is placed in 

 oxygen, or in an atmosphere containing oxygen under such conditions 

 that it volatilises, the phosphorus oxidises, partly into phosphoric 

 oxide, and partly into phosphorous oxide ; ozone is formed, possibly 

 in the mode already indicated, and this reacts upon the residual 

 phosphorus vapour and the phosphorous oxide with the production of 

 the luminous effect to which the element owes its name. The glow 

 itself is nothing but a slowly burning flame having an extremely low 

 temperature, caused by the chemical union of oxygen with the vapours 

 of phosphorus and phosphorous oxide. By suitable means this glow 

 can be gradually augmented, until it passes by regular gradation into 

 the active vigorous combustion which we ordinarily associate with 

 flame. Many substances, in fact, may be caused to phosphoresce in a 

 similar way. Arsenic, when gently heated, glows in oxygen, and 

 sulphur may also be observed to become luminous in that gas at a 

 temperature of about 200°. 



[T. E. T.] 



