114 ELEMENTS OF LABORATORY WORK 



Prepare a similar apparatus, but maintain an atmosphere of coal-gas 

 outside the porous vessel by the assistance of a vessel enclosing it, and 

 note that a quantity of gas passes to the inside of the porous vessel. 

 Write out a probable explanation of your observations, and suggest 

 methods of continuing the research. 



2. Ascertain by experiment the alteration of pressure produced by a 

 given change of temperature in a quantity of air maintained at the 

 same volume. Use a bent tube containing mercury and connect it with 

 a flask ; bring the air in the flask to its original volume by causing it 

 to support a lengthened column of mercury. 



3. Make experiments with a view to compare the physical properties 

 of indiarubber, glass, copper, and sealing-wax. Indiarubber tubing, glass 

 tubing or rod, and copper wire may be used. Pay special ..attention to 

 elasticity, rigidity, ductility, malleability. As a result of your observa- 

 tions, define the properties mentioned in a more accurate and complete 

 manner, and suggest explanations derived from the theory that matter 

 is formed of very small particles. 



4. Construct apparatus, and make observations of the amount of 

 evaporation taking place from a liquid water, for example into a known 

 quantity of air at different temperatures. 



6. Show by experiment that equalisation of pressure in gases takes 

 place rapidly, while the process of diffusion is comparatively very slow. 

 How is this explained 1 Modify the apparatus of fig. 32. 



6. Find out, by weighing the solid left after evaporation, the relative 

 quantities of common salt dissolved by water at the temperature of the 

 room, and by boiling water. 



7. Prepare crystals from powdered copper sulphate. What bearing 

 has the molecular theory of matter upon the formation of crystals ? 



8. How does the rate of evaporation and of solution depend upon 

 (1) rate of diffusion and (2) temperature ? 



9. In what sense can one gas be said to act as a vacuum towards 

 another ? 



10. Describe methods by which the rate of diffusion of gases or 

 liquids may be determined. 



11. Give a list of the chief facts which are reasonably explained by 

 the molecular theory of matter. 



12. Describe the various kinds of changes which might be expected 

 to take place in a system of molecules if it resemble a system of visible 

 bodies. 



13. Describe some process of determining the mass of a given volume 

 of water-vapour or steam. How will the presence of water-vapour in 

 the air affect the height of the barometer ? 



14. State why the surface of mercury in a glass tube is convex while 

 that of water is concave. 



