56 LETTEES OF BEEZELIUS 



when our reagents are unable to detect the presence 

 of any foreign body in it. 3. Chemical method of 

 formation. Phosphorus in a state of slow combustion 

 exerts a catalytic action on the oxygen and nitrogen 

 in contact with it, causing the former to combine 

 with the hydrogen of the latter and set the ozone 

 free. Part of this ozone appears as a gas and mixes 

 with the air, while another part combines with the 

 phosphorus to form phosphorus ozonide, which is de- 

 composed by the water present into phosphoric acid 

 and hydrogen ozonide, i.e., nitrogen. This is the 

 reason why in moist atmospheric air the oxidation 

 of phosphorus proceeds so comparatively fast, and it 

 also explains the fact, that in the slow combustion of 

 phosphorus in air, not only phosphorous acid is pro- 

 duced, but also phosphoric ; the latter is undoubtedly 

 formed by means of ozone, while the immediate 

 result of the slow oxidation of the phosphorus is the 

 production of the former. 



Similarly in the light of the facts which I have 

 discovered we can understand the long known and 

 remarkable property of nitrogen, of supporting the 

 luminescence of phosphorus. According to my ex- 

 periments, air standing over phosphorus and calcium 

 chloride does acquire a power of turning my test 

 paper blue, but very little ozone is formed under these 

 conditions, and hence very little phosphoric acid, 

 because the air cannot at first contain any water 

 vapour, and the water produced by the action of the 

 oxygen on the hydrogen ozonide is mostly absorbed 

 by the calcium chloride. Probably the formation of 



