168 INTRODUCTION TO GENERAL SCIENCE 



may be well to wrap the bottle with string. Leave until next 

 day, and explain the result. 



6. It is advisable to make all of the osmotic pressure cells 

 at one time, or the teacher may make only one and show its 

 action to the class. 



Make a saturated solution of copper sulphate and a satu- 

 rated solution of potassium ferrocyanide solution. Fill the 

 porous cup with the potassium ferrocyanide solution, wait 

 five minutes, and then place the porous cup in the copper sul- 

 phate solution. The two solutions will then meet somewhere 

 within the walls of the porous cup. Leave for half an hour. 

 Save the solutions. 



Fill the osmotic cell (porous cup) with a saturated solution 

 of sugar, insert the long tube in the stopper, and push the 

 stopper firmly into the porous cup so that the solution runs a 

 few inches up the tube. Now set the osmotic cell in the bat- 

 tery jar and fill the jar until the water stands at the same 

 level as the sugar solution in the tube. If the osmotic cell is 

 good, the solution will rise in the tube. If it does not do so, 

 remake the cell. 



120. REMOVAL OF GREASE SPOTS AND STAINS 



For the removal of stains we have at our command three 

 methods: solution, capillarity, and chemical action. The 

 method to be employed must be determined by its effect on 

 the material which is being cleaned. For that reason the use 

 of chemical action is somewhat limited, while some solvents 

 affect dyes. 



To remove grease by solution, use ammonia water, gasoline, 

 naphtha, benzine, alcohol, or ether. Ether is the most expen- 

 sive, but it can dissolve some substances better than any other 

 solvent. 



