CHAPTER XVIII. 

 EXAMINATION OF COMMON SUBSTANCES. 



35. EXAMINATION OF SAND. 



i. Examine the sand supplied as directed in Chapter XVII. Solubility 

 need not be tested. Why ? 



ii. Form Examine a portion of the sand with a lens. 



Sand. Sand is generally a pale yellowish or brownish, tasteless, 

 odourless crystalline powder. From the fact that it is sometimes seen 

 suspended in the surf by the seashore it, is concluded that it is not 

 much denser than water, in which it does not dissolve. It scratches 

 the blade of a penknife and is therefore harder than it. On account of 

 this property fine sand is used for polishing metals. 



Examination with a lens shows that each little grain is transparent 

 like glass ; the edges of it are smooth, due to rubbing against other 

 particles. The fact is that each grain is really a fragment of quartz 

 or a portion of a ' rock ' from which it has become detached. 



When heated in a test-tube sand does not appear to change ; but 

 when heated very strongly with an oxy-hydrogen flame it can be melted, 

 and made into test-tubes, etc., which have an appearance like glass. 

 Quartz vessels made in this way have the advantage over glass that they 

 can be subjected to sudden changes of tempera tiire without breaking. 



Certain kinds of sand are used in the manufacture of ordinary glass. 

 Sand is also used along with lime in the making of mortar. 



36. EXAMINATION OF CHALK. 



i. Examine a specimen as directed in Chapter XVII. 



ii. Does chalk dissolve in water ? When powdered chalk is shaken up 

 with water, a " milky " liquid is produced, due to the fact that fine particles 

 of the chalk are suspended in the liquid. If the test-tube is allowed to stand 

 for a time, the chalk will settle to the bottom, leaving a clear liquid on top. 



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