EXERCISE VII. 

 WATER— A COMPOUND ESSENTIAL TO ALL PLANTS. 



Supplies for a Laboratory Section of Twelve. A few grams of zinc; 500 cc. flask; a little diluted sulphuric 

 acid; one-hole rubber stopper to fit flask; pipette; glass funnel; a cigar box filled with air-dry silt soil; twenty- 

 four test tubes; sawdust; meat; salt; twelve evaporating dishes; distilled water or rain water; twelve glass tubes 

 about 7" long; limewater; vinegar; olive oil; twelve glass plates 4"x4" ; twelve one-hole rubber stoppers to fit test 

 tubes; twelve elbow tubes. 



Part A. Chemical Composition of Water. 



1. (Classroom experiment.) Place a few grams of zinc in a 500 cc flask. Add enough 

 diluted sulphuric acid to cover well. Fit the flask with a pipette in order that the gas may 

 be burned as it is given off. Hydrogen gas, when mixed with air, is explosive, so before light- 

 ing the gas as it escapes from the pipette, first collect a test tube full of the gas. Remove the 

 test tube full of gas a little to one side and apply a lighted match. If the gas in the test tube 

 burns quietly it will be quite safe to light the gas as it escapes from the generator. After light- 

 ing the gas at the generator, hold a cool glass funnel or beaker over the flame, (a) Ob- 

 serve what collects on the glass, (b) When hydrogen burns in air, it unites with the oxygen 

 of the air to form what? 



Part B. Distribution of Water. 



2. Place enough air-dry soil in a test tube to fill the rounded part. Heat very gently. 

 Observe whether or not moisture collects within the tube just above the soil, (a) What is 

 the source of this moisture? 



3. Recall having seen moisture collect on the surface of a pitcher filled with water, (a) 

 Under what conditions does this occur? 



Recall having seen moisture collect on windows, (b) What conditions are necessary to 

 produce this phenomenon? (c) Infer the source of such moisture. 



4. Place enough dry sawdust in a test tube to fill the rounded part. Heat very gently, 

 (a) Observe any change within the tube. (b)What is the source of this moisture? 



5. Place a piece of meat the size of a pea in a test tube. Heat gently, (a) Observe 

 what collects within the tube. above the heated part, (b) What is the source of the moisture 

 observed? 



6. The four preceding experiments show what to be true of the distribution of water in 

 nature? 



Part C. Solvent Power of Water. 



7. Place enough salt in a test tube to fill the rounded part, then fill the tube half full 

 of water. Shake well, (a) Observe the appearance of the water and its taste, (b) Infer 

 concerning the presence of salt in any part of the liquid, however small. Evaporate to dry- 

 ness a little of the solution in an evaporating dish, (c) Compare the substance left with salt, 

 (d) How may you determine whether or not a liquid holds a solid in solution? 



8. Add a few drops of vinegar to a little water in a test tube, (a) Observe the appear- 

 ance and taste of the liquid, (b) Infer concerning the presence of vinegar in any part of the 

 water, however small. Add a drop of olive oil to water, (c) Infer concerning the solubility 

 of olive oil. (d) Infer concerning the solubility of vinegar. 



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