386 Prof. H. E. Armstrong on Lon-- Temperature Research 



anhydride cannot be credited with absohite dehydrating- power ; 

 and although water vapour cannot well have remained in the bulb, 

 it must be granted that a certain proportion of simple molecules of 

 hy drone (OH^) may have been present together with the phosphorus 

 molecules. We are perhaps too much in the habit of associating' 

 the properties of water with those of the hydrone molecule : being 

 lighter than that of most gases, the simple molecule of water must be 

 highly volatile, although more prone than most molecules to adhere to 

 surfaces with which it may come in contact. 



Photographic Action at Loio Temperatures. — In the Bakerian 

 lecture delivered to the Royal Society in 11)01, Sir James states that 

 " Photographic action is still active at the temperature of boiling- 

 hydrogen although it is reduced to about half the intensity it bears 

 at the temperature of liquid air." This apparently is a confirmation 

 of his previous conclusion based on experiments made with liquid air, 

 that such action cau take place at low temperatures and in absence 

 of moisture. The sul)ject is a difficult one to discuss, owing to our 

 ignorance not merely of the actual nature of the effect produced ])y 

 light on tlie sensitive silver salt but also of the nature of the active 

 " system." Even assuming, however, that it be the silver haloid alone, 

 although this is^^er se an electrolyte in the viscous or fluid state, it is 

 probably not one in the rigid state ; and the same argument would 

 apply to any system composed of the haloid and a sensitiser : there- 

 fore it should not be sensitive to light at low temperatures. It is 

 perhaps not improbable tiiat the photographic effect is the result of 

 autoexcitation consequent on the phosphorescence which Sir James 

 has shown to l)e conditioned in so many sul)stances by exposure to 

 light at low temperatures. 



In calling attention to the bearing of all these different results 

 on the one problem, I am led by the desire to lay all possible 

 emphasis on their importance and the need of further inquiry. 



Solid Fluorine. — The liquefaction of fluorine during the earUer 

 period has now been followed by its solidification by means of liquid 

 hydrogen. The yellow liquid is converted into a white soUd,* melting 

 at about -40^ absolute, a temperature a little below that at which solid 

 oxygen melts. When the point of a tube containing solid fluorine 

 plunged in liquid hydrogen was broken off by means of steel pincers 

 a violent explosion took place. 



A further series of observations on the interactions of liquid 

 fluorine with substances previously cooled in liquid air have been 



* Chlorine also becomes white when it solidifies. In the account given to 

 the French Academy of these experiments (Comptes Rendus, cxxxvi. 642), it 

 is implied that bromine is colourless when solid. This is incorrect. I am 

 informed by Sir James Dewar that it only becomes somewhat paler in colour. 



