72 



FIRST TEAR SCIENCE 



to which the hydrometer sinks in the water. In a dish sufficiently 



deep for the hydrometer to float dissolve a considerable quantity of 

 salt in water. After the salt has become thoroughly 

 dissolved taste the water at the top and then after pour- 

 ing off the larger part of the water taste that at the 

 bottom of the dish. The salt is present in all the water 

 but the appearance of the water has not changed. 



Now place the hydrometer in the water containing 

 the dissolved salt. It does not sink to the same depth 

 that it did in the fresh water. What can be said about 

 the buoyancy of water which contains substances in 

 solution? Does a fish need to exert muscular force to 

 float in water? Since water contains many substances in 



solution, it is possible for a water animal that does not move to 



be continually supplied with food. 



Fig. 41. 



Experiment 36. (Teacher's experiment). Place a small handful of 

 zinc scraps in a strong wide-mouthed bottle. Fit the bottle with a 

 two-hole rubber stopper having a thistle tube extending through one 

 hole and a bent delivery tube through the other. The thistle tube 

 should reach nearly to the bottom of the bottle. Connect the delivery 

 tube with the shelf of a pneumatic trough by a rubber tube. 

 Have several inverted 8 oz. wide-mouthed bottles filled with water 

 on the shelf of the trough. Pour enough water through the thistle 

 tube to partly cover the zinc and then pour on commercial hydro- 

 chloric acid or sulphuric acid diluted 1 to 10. 



Chemical action will take 

 place between the zinc and 

 the acid and hydrogen will 

 be freed. Allow the gas to 

 escape for several minutes, 

 as this is largely the air 

 which was in the bottle. 

 Collect several bottles full 

 of the hydrogen. Keep the 

 bottles inverted. Examine 

 the hydrogen in one of the 

 bottles. Has it color or odor ? 



Fig. 42. 



Holding the mouth downward thrust a lighted splinter iYito an- 

 other bottle. The splinter does not continue to burn in this gas 

 but the gas itself burns. Place another bottle mouth up on the 



