VARIETIES. 
375 
Prof. Marchand has now proved the correctness of this opinion by a 
number of carefully performed experiments, the result of which is that 
phosphorus emits light in all gases and vapors with which it does not chemi- 
cally combine. In some gases the temperature may be very low, and in 
others it must reach the boiling point of phosphorus. 
The emission of light is, therefore, only a consequence of evaporation, 
during which very probably molecular changes take place. It differs from 
that which occurs when phosphorus becomes oxydized, and both kinds 
of luminous appearances may separately occur. The emission continues 
as long as the phosphorus is able to evaporate and has tension. It 
ceases when the phosphorus is? covered with some coating, by which 
evaporation is impeded. The tension is excessively low at a temperature 
of 15° C, but the emission of light does not become imperceptible 
until 22° C. 
In a current of hydrogen, or carbonic acid perfectly devoid of oxygen, 
and at a proper temperature, phosphorus continues to emit light, as long 
as the vapors are carried off ; neither litmus or starch with iodide of potas- 
sium betray any alteration, consequently, neither oxydation, nor formation 
of ozone, nor any change of the phosphorus takes place. It merely evapor- 
ates, and retains its vitreous condition in the dark, even when the experi- 
ment has been continued for many days. 
If the experiment be performed in closed vessels, the development of 
light ceases after a short time, but only in consequence of the developed 
vapors impeding evaporation. As soon as this obstacle is removed, the 
emission of light reappears. The same also occurs on the Torricelian 
vacuum. 
It is well known that gases and vapors which combine with phosphorus, 
e. g. the volatile oils and the different kinds of ether prevent its evaporation. 
It therefore follows that phosphorus emits no light in hydrogen, which has 
been deprived of oxygen by potassium, if the latter was contaminated with 
naphtha. 
In compressed air phosphorus ceases to evaporate. Dr. J. Davy has 
stated, that a pressure of four atmospheres is necessary for this ; but, 
Marchand found, that at a temperature of 50° C. two atmospheres suf- 
ficed to extinguish the phosphorus in dry atmospheric air. The same is 
the case with hydrogen and carbonic acid, if the pressure is suddenly 
removed ; then not only does the phosphorus itself emit light, but 
there arises also a luminous vapor. The light disappears, however, 
as soon as the space is filled with the phosphorus vapor. When phos- 
phorus becomes luminous in atmospheric air, not only evaporation but 
also combustion goes on, and in consequence, litmus paper is colored red. 
Substances chemically related to phosphorus, such as sulphur, selenium, 
arsenic, and antimony, when they are vaporized, do not evolve light. But 
if the experiment be done in atmospheric air, these substances also possess 
