6 STUDIES IN PHYSIOLOGY 



Close to the earth this air is comparatively dense. But if 

 one could rise in a balloon from the surface, one would find 

 that the air becomes more and more rare, and that it almost 

 ceases to exist at a height of thirty to sixty miles. One of 

 the constituents of the atmosphere is a gas called ox'y-gen. 

 When we take the phosphorus from the water, we expose it 

 to this omnipresent oxygen of the air. This is all that is 

 necessary, for the mutual attraction between phosphorus 

 and oxygen is so great that the two straightway combine to 

 form a new substance. 



We saw the white fumes rising from the phosphorus and 

 noticed that some of the latter disappeared. If we measured 

 the exact amount of oxygen in the air before and after the 

 experiment, we should find that small quantities of this 

 gas also had disappeared. The white fumes are therefore 

 formed by a chemical union of phosphorus with oxygen, 

 and since the fumes are composed of these two substances 

 alone, the new compound is called an oxid of phosphorus. 



Every time we draw a match across our fingers, we cause 

 a little of the phosphorus to combine with surrounding oxy- 

 gen, and we notice the peculiar smell of oxid of phosphorus. 

 When we scratch the match more forcibly against a rough 

 surface, we hasten this process by causing the heated 

 phosphorus to combine rapidly with the oxygen gas of 

 the air, and thus a flame is produced. In this chemical 

 union both phosphorus and oxygen seem to disappear. 

 They are not lost, however ; for on decomposing or analyz- 

 ing the white fumes we find all of the phosphorus we had at 

 first and all of the oxygen taken from the air. 



Sulphur and Oxid of Sulphur. Let us light another match 

 and continue our study. Soon after the white fumes of 

 oxid of phosphorus begin to appear, we notice the suffocating 

 odor of burning sulphur. The sulphur of commerce is 

 usually obtained from mines near active or extinct vol- 

 canoes and comes to us in the form of a yellow powder or 

 of solid brimstone. If we treat a bit of it as we did the 



