298 ELEMENTARY GENERAL SCIENCE CH. xxi 



precipitate, if collected and mixed with hydrochloric acid, dissolves 

 with effervescence. What experiments would you make in order to 

 compare the gas thus obtained with that obtainable from the 

 breath ? 



21. Three bottles filled with colourless gas are placed before you 

 containing (a) hydrogen, (6) nitrogen, and (c) carbon dioxide. De- 

 scribe experiments you would make in order to distinguish them 

 from one another, and from other gases. 



22. Describe and explain the changes which take place when (a) 

 limestone is burnt in a kiln, (6) water is added to some freshly burnt 

 lime. 



23. How is lime distinguished from limestone as to composition 

 and properties ? 



