Mingling of Molecules 265 



385. Piano keys may be cleaned with alcohol. 



386. Linemen working with live wires wear heavy rubber gloves. 



387. Crayon will not write on the smooth, glazed parts of a black- 



board. 



388. Varnish and shellac may be thinned with alcohol. 



389. Filtering will take mud out of water, but it will not remove 



salt. 



390. Explain why only one wire is needed to telegraph between 



two stations. 



SECTION 42. Crystals. 



How is rock candy made ? 



Why is there sugar around the mouth of a syrup jug? 



How are jewels formed in the earth? 



You can learn how crystals are formed and many 

 gems and rock candy and the sugar on a syrup jug 

 are all crystals by making some. Try this experi- 

 ment: 



Experiment 83. Fill a test tube one fourth full of powdered 

 alum; cover the alum with boiling water; hold the tube 

 over a flame so that the mixture will boil gently ; and slowly 

 add boiling-hot water until all of the alum is dissolved. Do 

 not add any more water than you have to, and keep stirring 

 the alum with a glass rod while you are adding the water, 

 Pour half of the solution into another test tube for the next 

 experiment. Hang a string in the first test tube so that it 

 touches the bottom of the tube. Set it aside to cool, un- 

 covered. The next day examine the string and the bottom 

 of the tube. 



Experiment 84. While the solution of alum in the second 

 test tube (Experiment 83) is still hot, hold the tube in a pan 

 of cold water and shake or stir it until it cools. When 

 white specks appear in the clear solution, pour off as much 

 of the clear part of the liquid as you can ; then pour a little 

 of the rest on a glass slide, and examine the specks under a 

 microscope. 



