CHEMICAL CHANGE AND THE METHODS OF STUDYING IT 25 



properties are utilized in manipulations, like nitration and evapo- 

 ration, as well as for identifying substances, and that physical 

 attributes are used for measuring quantities in chemistry and 

 physical conditions for guiding chemical change. Finally, we 

 have seen that a science is not a natural, but a manufactured 

 product, and that the science of chemistry is still in the making. 



Exercises.* 1. What physical properties are used (a) in 

 filtration, (6) in evaporation, (c) in the separation and identifica- 

 tion of the products from heating mercuric oxide (p. 15)? 



2. Describe: (a) a red-hot rod of iron, 10 cm. long by 1 cm. 

 diameter, weighing 58.5 g.; (6) a solution of 5 g. of sulphur in 

 20 c.c. (26 g.) of carbon disulphide at 18 C. In doing so, divide 

 the description into attributes, conditions, and properties. 



3. Consider the following materials and state whether, so far 

 as you can now judge, each is a single substance or a mixture: (a) 

 a candle, (fe) a cake of soap, (c) an egg. 



4. What are the two most direct ways of showing a substance 

 to be a compound? Illustrate each. 



5. If we say that quicklime contains calcium, do we mean the 

 element or the simple substance calcium? 



6. What explanation was given, (a) of the disappearance of 

 mercuric oxide when heated, (6) of the absence of iron and sulphur, 

 as substances, from ferrous sulphide? Which of the three kinds 

 of explanation was used in each case? 



7. What weight of oxygen will be required to combine with 15 

 grams of lead (p. 10)? 



8. If 5 grams of lead and 4 grams of oxygen were heated 

 together, which of the two would remain in part unused? How 

 much of this one would remain (p. 10)? 



* The exercises should in all cases be studied with minute care. They not 

 only serve as tests to show that the chapter has been understood, but very 

 frequently (as in No. 4) also call attention to ideas which might not be ac- 

 quired from the text alone, or (as in Nos. 1, 2, 5) assist in elucidating ideas 

 given hi the text which, without the exercises, might not be fully grasped. 



