ADHESION OF LIQUIDS TO SOLIDS; LIQUID SURFACES 11 



with water. What is the shape of the edge of the water sur- 

 face? Dip into the water a glass tube or rod that is covered 

 with grease or vaseline. What is the shape of the surface 

 around the tube (or rod)? 



If a liquid wets a solid, will the liquid surface be lifted up, or 

 pushed down, next to the solid? If the liquid does not wet the 

 solid, what will the result be? What is the effect on the liquid 

 surface when you dip a nail into water? A silver spoon? A 

 pencil? 



c. Put a drop of water upon a freshly washed, but dry, 

 piece of glass. What shape does the drop take? Draw a 

 sketch showing this. Put a drop of water upon a greased paper. 

 Its shape? On a kneading board dusted with flour. The 

 result? 



d. Put a drop of water on a stove top that is not red hot. 

 What is the shape of the drop? Then put a drop of water upon 

 a red-hot sheet of iron, such as a stove lid. What is the shape 

 now? If your family uses a gas range, put a thin sheet of iron 

 (a piece of "tinned" iron or a flat "tin" cover will do) over the 

 gas flame until it is red hot; then add the water drop. 



e. Let water drop into a graduated cylinder, ami count the 

 number of drops in 10 cu. cm. You can get water to form drops 

 on a faucet, or you can make a tiny hole in the bottom of an 

 empty tin can, so that the water will leak out drop by drop. 

 Make at least three trials, and get the average. Calculate how 

 many drops of water there are, under ordinary conditions, in 

 1 cu. cm. Put down all results in systematic form, as in 

 Exercise 2. Make a sketch showing the stages in the formation 

 of a water drop. 



/. Wipe a needle clean, and then oil it very slightly with 

 vaseline or machine oil. Hold the needle horizontal on a fork; 

 then lower the fork carefully into a bowl or soup plate of water. 

 The needle should float. Examine the water surface, and tell 



