96 LABORATORY LESSONS IN GENERAL SCIENCE 



7. What is the active chemical agent in the hypochlorite 

 of lime (and "bleaching powder") used to purify the water 

 supply in city water systems, the soiled clothing from per- 

 sons sick with infectious diseases, and the air of cellars and 

 basements not kept well ventilated? Name several other 

 disinfectants whose value lies in their chemical action upon 

 disease germs. 



THE CHEMISTRY OF CLEANING 



1. For scrubbing floors, washing windows and table dishes, 

 and for toilet and laundry purposes, soap is employed to an 

 extent that has led to the statement that the civilization of 

 a nation may be judged by the amount of soap its people use. 



What in general is true of dissolving oils and fats in water, 

 either cold or warm? What is the nature of butter? In 

 what size of particles must its material be when scattered 

 through milk ? Ascertain the meaning of the term emulsion, 

 and show how it applies to milk. 



2. What is a common effect upon the skin of the use of 

 laundry soap ? Test some strong soap solution with a strip 

 of red litmus paper. If it is turned blue, the soap solution 

 is said to have an alkaline reaction (or alkaline effect). De- 

 termine by use of litmus paper whether laundry soap or 

 toilet soap is more alkaline. What should be true of toilet 

 soaps with regard to an excess of alkali? Ascertain the 

 nature of (a) scouring soaps; (b) "sapolio." 



3. Why is "hard water" objectionable for toilet and 

 laundry purposes ? Why is cistern water more satisfactory ? 

 Why is not cistern water available for household purposes 

 everywhere? Where "soft water" is not available for 



