34 LABORATORY EXERCISES 



circular filter through the middle, and then fold each half. 

 Press the folded edges between the thumb and forefinger, but 

 not between the nails. Open the filter so that it forms an in- 

 verted cone, and fit the cone exactly into the funnel. Hold the 

 filter in the funnel, wet it with water, and press it carefully 

 against the sides of the funnel. 



Stir the mixture of sand, salt, and Water, and pour the solid 

 and liquid together upon the filter. Catch the part that runs 

 through (the filtrate) in a dish, and evaporate some of it on a 

 watch glass or a glass plate over a cup of boiling water (refer to 

 Exercise 29, c). What substance do you obtain? 



b. To 2 cu. cm. of a solution of potassium dichromate add 

 twice its volume of a solution of lead nitrate or of lead acetate 

 (" sugar of lead")- What happens? Let the solution stand; 

 what settles out? 



An insoluble solid that is formed by the mixing of solutions is 

 called a precipitate. What color has the precipitate in this case? 

 Filter it off, spread out the filter paper, and let it dry. The 

 powder consists of " chrome yellow," used in the making of 

 certain yellow paints. Evaporate the filtrate; it contains 

 "niter," or "saltpeter." 



What is the color of the precipitate formed when carbon 

 dioxide is mixed with lime water? Refer to Exercise 15, a. 



EXERCISE 32 

 CRYSTALS 



Apparatus and Materials. Powdered alum, beaker or cup, water, 

 burner. 



a. Put 10 cu. cm. (about 2 teaspoonfuls) of powdered alum 

 into a beaker or cup, and add 20 cu. cm. of water to it. Stir 

 the mixture for several minutes. Does some alum dissolve? 



