90 ANSWERS TO PRACTICAL QUESTIONS 



18. Write in parallel columns the properties of com- 

 mon and of red phosphorus. 



Common phosphorus. 



1. Specific gravity 1.83. 



2. Burns at 111. 



3. Odor of garlic. 



4. Soluble in CS 2 . 



5. Colorless, or straw-yellow. 



6. A deadly poison. 



Amorphous phosphorus. 



1. Specific gravity 2.14. 



2. Burns at 500. 



3. Odorless. 



4. Insoluble in CS 3 . 



5. Brownish red. 



6. Harmless. 



19. IVTiat causes the difference between fine and coarse 

 salt ? 



(See Chemistry, p. 132.) 



The rapidity of evaporation in the process of manufacture. 



20. WJiy do the figures in a glass paper-weight look 

 larger when seen from the top than from the bottom ? 



The form of the glass acts like a convex lens to magnify 

 the apparent size of the figures. 



21. What is the difference between water-slacked and 

 air-slacked lime ? 



The former is simply calcium hydrate, CaO, H 2 O, while the 

 latter has absorbed both H 2 O and CO 3 from the air. 



22. Why do oyster-shells on the grate of a coal-stove 

 prevent the formation of clinkers ? 



The lime of the shells acts as a flux with the iron in the 

 coal, thus dissolving the clinkers, if any form. 



23. How is lime-water m,adefrom oyster-shells ? 



The shells are burned, driving off the CO 2 combined with 

 the CaO in the CaCO 3 , and the lime thus formed is slightly 

 soluble in water. 



24. IVliy do newly plastered walls remain damp so 

 long? 



The plaster or mortar in drying gives off the water the 

 lime took up in slacking. 



