228 



ELEMENTARY GENERAL SCIENCE 



CHAP. 



draws a current of air through the tube, and, in order to dry 

 the air, it is first made to pass through the test tube (7, con- 

 taining strong sulphuric acid. Warm the phosphorus slightly 

 it ignites. Take away the burner and allow it to burn, the 

 fumes being stopped by the asbestos. A quantity of red 

 deposit is also found (another form of phosphorus), and this 

 may be got rid of by strongly heating. When cool, dis- 

 connect, and again weigh the tube. It is found, if carefully 

 done, that the phosphorus gains about 128 per cent. 



Ex FT. 231. If we desire to do the same with sulphur, we 

 must alter our apparatus, as the product is a gas. This is 

 readily done. The tube BA, as before, contains the sulphur, 



Strong 

 Solution 

 ofcaujtCc 

 Potash/ 



FIQ. 115. Burning Sulphur in a Current of Air. 



but the air together with the products of combustion are 

 drawn through a strong solution of caustic potash in the test- 

 tube D, the air having been previously drawn through the tube 

 G containing strong sulphuric acid (Fig. 115). The sulphur di- 

 oxide is absorbed in _D, so that if this tube be weighed before 

 and after the experiment we obtain the weight of the gas, while 

 the weight of the tube AB with sulphur in it (1) before heating 

 (2) after heating gives the weight of sulphur which has burnt 

 away. From these results calculate the increase of weight 

 for 100 grms. of sulphur. It is seen that the sulphur gains 

 100 per cent. 



Combustion and Rusting. A comparison of these ex- 

 periments with those on the rusting of iron should be made in 



