PROBLEM I . The Composkloii of Living Things 1 1 7 



18. Is salt water a compound or a mixture? How can you find out? 

 Do this experiment at home. 



19. Answer the following questions: (a) Are the gases oxygen, nitro- 

 gen, carbon dioxide, and water vapor, which make up the air, mixed 

 together or is air a compound? Give scientific evidence for your answer. 

 (b) The chemist speaks of water as HoO. What is the meaning of the 2 

 after H? Carbon dioxide is COo. What are the proportions of C and O? 

 Carbon monoxide consists of carbon and oxygen. The prefix "mon" 

 means one. Write the formula for carbon monoxide, (r) Ordinary granu- , 

 lated sugar is C^.^rioX)^^. What do you know about its composition? 



Further Activities in Biology 



1. You can easily learn to prepare slides. Which is the best way of 

 putting on the cover glass so that bubbles will not form? Consult books 

 or ask your teacher for further help. In time you will probably want 

 to learn how to make microscope slides which are permanent. This is 

 difficult and takes patience. 



2. Can you think of some way of making a model of a cell which will 

 give your classmates a good idea of how a cell really looks? (Do not for- 

 get that protoplasm is transparent.) 



3. Prepare a report on the history of the microscope. 



4. Prepare a demonstration other than that used in the text to show 

 how elements change their nature when combined into compounds. 



5. Prepare a demonstration of the compounds found in living things. 

 Try to get many diff^erent examples of each class of compounds: many 

 starches, many sugars, and so on. 



