Air 213 



144. It is probable that, from the above experi- 

 ment, a rough idea of the volume of gas which 

 remains, and does not assist in the burning, may be 

 obtained. 



To measure this volume more accurately, the follow- 

 ing experiments may be performed : 



EXPERIMENT 80. Down the side of a tall gas- jar 

 paste a long strip of paper divided into centimetres and 

 half-centimetres, the centimetre divisions being num- 

 bered in order, commencing from the closed end of the 

 jar. Cover this paper strip with a layer of paraffin 

 wax by means of a camel-hair brush dipped in some 

 melted wax. 



Half fill an earthenware trough with water. With 

 a blunt knife blade, carefully scrape clean a small stick 

 of yellow phosphorus about half an inch long, the 

 phosphorus being held under water while scraping it. 

 Coil a length of rather stout copper wire, as shown 

 in Fig. 66, so that the diameter of the larger 

 coils at the top is slightly greater than that 

 of the phosphorus. To the lower end of 

 the wire attach a flattened leaden bullet (or 

 other small flat heavy substance) of sufficient 

 weight to keep the wire upright when the 

 flat surface is resting on the table. Put the 

 freshly scraped stick of phosphorus into 

 the coil (see Fig. 66). Invert the gas-jar 

 previously prepared, and push the phos- Fig> 66 - 

 phorus up into it by means of the wire, the length of 

 which should be such that the phosphorus reaches the 

 middle of the jar. Lower jar and contained wire into 

 the water in the earthenware trough, so that they 

 occupy the position shown in Fig. 67. 



Record the length of the column of air within the 



