86 



Mr. Graham's Observations on 



these limits. A pretty strong combustion occurred at 240°. 

 The following table exhibits the temperature at which phos- 

 phorus first becomes faintly luminous in the dark in air con- 

 taining different gaseous substances : — 



In 1 volume of air and 1 volume of defiant gas, at 



3 „ 2 „ vapour of ether, at 



111 „ 1 , vapour of naphtha . 



166 „ 1 „ vapour of turpentine, at 



200° F. 

 215° 

 170° 

 186° 



The manner in which the influence of these gases is modified 

 by barometric pressure is the most curious part of the subject. 

 The proportion necessary to prevent combustion depends en- 

 tirely upon the density of the gases. Thus, although less than 

 one four-hundredth part of olefiant gas prevents the combus- 

 tion of phosphorus, barometer 29 inches, phosphorus has been 

 observed in a luminous state, under the pressure of half an 

 inch mercury, in air containing so much as an equal volume 

 of that gas. 



In the following table the first column of fractions expresses 

 the largest proportion of olefiant gas, in a mixture of air and 

 that gas, which allows phosphorus to be luminous under the 

 pressure placed against it. A greater proportion of olefiant 

 gas extinguishes at that pressure. 



Thermometer at 70°. When phosphorus is luminous above 

 the mercurial column in a barometer tube at the greatest pres- 



