82 



LABORATORY EXERCISES 



What is the color of each? Is the material all of one color, 

 or of different colors? Which substances are crystalline? 

 See 69 of text. "Heft" each substance to determine whether 

 it is dense or light. 



b. Try to scratch each substance, with 



1. Your finger nail. 



2. A cent piece. 



3. A knife blade. 



4. A triangular steel file. 



Which of the substances scratch glass? 



c. On the surface of each piece put a drop of hydrochloric 

 acid (1 cu. cm. of the concentrated acid to 3 cu. cm. of water). 

 Do any of them effervesce; that is, get frothy and give off tiny 

 bubbles of gas? 



How can you distinguish rock salt from all the others? 



d. Classify your results under the following heads: 



EXERCISE 80 

 CONCRETE 



Apparatus and Materials. Tin can (tomato can), measuring cup, 

 wooden paddle or iron spoon, block for "tamp," pasteboard box 

 (small), cement, sand, and gravel. 



