120 



CHEMISTRY. 



[Lesson IX. 



3. Describe the specific gravity of a 

 fluid, a solid, and a gas. 



4. Describe the signification and pro- 

 cesses of pulverization, trituration, levi- 

 gation, and granulation. 



5. Describe the processes of sifting, 

 elutriation, and filtration. 



6. What means have we of obtaining a 

 greater heat than that furnished by an 

 ordinary fire ? 



Fig. 2S. 



LESSON IX. 



Now that we have become acquainted with the general principles and leading points 

 of chemistry, we shall be better prepared to commence the investigation of some of 

 the elementary bodies. The first group we shall consider is the gazolytes, consisting 

 of oxygen, hydrogen, and nitrogen. In order to make experiments with gases, we 

 must have a peculiar kind of apparatus, but it need not be expensive, and as we shall 

 require it very frequently, it will be better to construct it at once. First of all we shall 

 want a spirit-lamp, and therefore you had better cut off two inches of 

 brass tubing, and having fitted a small bottle (Fig. 28, d) with a cork, 

 bore a hole in its centre with a red-hot wire, and insert the piece of 

 tubing. Pass some cotton through the tube, () and fill the bottle up 

 to the shoulder with spirit of wine. It is better to have a tin cover (c) 

 fitted to the bottle, in order to prevent the evaporation of the spirit. 

 Select a piece of glass tubing, about the size of a goose-quill, and 

 long enough for your purpose (about eighteen inches) ; hold it over 

 the flame of the spirit-lamp, and heat it gradually ; it will soon 

 begin to soften, and you should then bend it to the shape of the one 

 in Fig. 29, and let it cool gradually. Fit a Florence flask with a sound cork, then make 

 a hole in its centre to receive the bent tube, and place the flask upon the ring of a 

 retort-stand (a 6), as in Fig. 29. The retort-stand is only an iron rod, fitted to a heavy 



base, and furnished with movable rings, 

 which can be fixed in any position by screws. 

 The pneumatic trough (t) is generally made of 

 tin, japanned, and has a movable shelf, to 

 support the receivers of jars in which the 

 gas is collected. It should be about 14 

 inches long, 9 wide, and 8 high, and when 

 used is filled with cold water. "When not 

 able to procure a trough and convenient re- 

 ceivers, a common washing-basin will form 

 a good substitute for the former, and a few 

 pickle bottles for the latter. 



When about to collect gases attend to th 

 following rules: 1st. Fill the receivers by immersing them in the trough ; then raise 

 them carefully and place them mouth downwards on the shelf in your trough ready for 

 use, taking care that the water is at least one inch above their mouths. 2nd. Before 

 collecting the gas for experiment allow some to escape, because the first portions are 

 always inferior. 3rd. Attend to the lutings and joints of the apparatus, to see that no 

 gas escapes. 4th. When you apply heat to the apparatus be sure to remove the end of 

 the gas-delivering tube (c d) from the water before you remove the heat, otherwise the 



Fig. 29. 



