I3 8 ANSWESS TO PRACTICAL QUESTIONS 



33. What is the antidote to oxalic acid ? Why ? 

 Magnesia or chalk, forming an insoluble oxalate. 



34. Would you weaken camphor spirits with water ? 



(See Chemistry, page 117.) 



No ; since camphor is insoluble in dilute alcohol. The 

 principle is the same as that of the precipitation of lead 

 from dilute oil of vitriol. 



35. WJiat is the difference between rosin and resin ? 



Rosin is an oxidized resin. Rosin is a species, and 

 resin a genus. 



36. Why does skim-milk look blue and new milk white ? 



The globules of butter contained in new milk reflect 

 the light, and so make it look white ; but when they are 

 removed, by the separation of the cream, more light is 

 transmitted, and only the blue is reflected to the eye. 



37. Why does an ink-spot turn yellow after washing with 

 soapl 



The free alkali of the soap combines with the tannic 

 acid of the ink, leaving the oxide of iron (ferric oxide), 

 which stains the cloth yellow. 



