74 Introduction to the Study of Science 



burning? Observe the rise of water in the jar. If limewater is used, 

 explain the change of color (page 124). Let the jar stand undisturbed 

 until its temperature is that of the room. Mark then the level of the 

 water in the jar. Taking the original level as indicated by the shorter 

 end of the glass tubing, how much air by volume has been used in the 

 burning ? How can you measure the volume ? What is the fractional 

 part of the original volume contained in the jar, again measuring from 

 the end of the tube ? After removing the tube, slip a piece of glass over 

 the mouth of the jar while in the water, and holding it securely invert 

 the jar. Slip the cover to one side and insert a burning splinter or 

 candle. What does the result show ? 



When the experiment with the iron filings is finished, compare re- 

 sults of both experiments. Is the volume of remaining air the same 

 in both cases? Does it have the same properties? If the products 

 are the same, is it justifiable to infer that the process is the same, 

 though very much slower in one case than in the other? 



Of the total amount of air imprisoned in the jar at the begin- 

 ning, approximately one fifth has been used in burning. This 

 part plainly supports combustion. 



35. The residual gas, nitrogen. The residual part of the 

 air, about four fifths of the original volume, shows by tests 

 that it does not support combustion. It remains in contact 

 with water with no appreciable decrease in quantity, and is 

 thereby shown to be not soluble in water to any great extent. 

 It remains in the jar, moreover, while you insert a burning 

 candle or match ; this indicates that it has about the same 

 weight, volume for volume, as the air. The fact that it does 

 not combine with the burning candle shows that, as compared 

 with the other one fifth of the air, it is sluggish and inert. 



The residual gas was perhaps first discovered by Scheele, 

 in experimenting with iron filings. Because this gas refused 

 to support combustion and seemed incapable of sustaining life, 

 Scheele called it " vitiated air." It was found to be abundant 

 in some well-known compounds, as saltpeter or niter (potas- 

 sium nitrate). Lavoisier, who made chemistry a measuring or 

 quantitative science, determined the actual importance of the 

 gas in the atmosphere, and because of its niter-forming nature 



