During winter, in the U.S. people add salt to melt the
  unwanted snow (on the roads). But in India, to make 
  ice-cream we were advised to add salt to the ice cubes
  amongst which the ice-cream is kept. Can anyone 
  explain the role of salt in these situations?                 216
Why molten wax which is transparent becomes opaque
  at normal temperature?                                        217
Why are iron pipes laid down in the entrance of some 
  main buildings?                                               217
Why do people swat more before a heavy rain?                    217
What is a biological weapon?                                    218
What is the role of superplasticizers in concrete?
  When are they preferred?                                      219
A newspaper is easily torn vertically but not horizontally.
  Why is it so?                                                 220
It is slightly difficult to neatly tear a dry sheet of paper.
  Also when torn, it produces noise. But it is easiear to 
  tear a wet paper, that too without noise. Can any
  one explain this?                                             222
Why does paper become translucent when smeared 
  with oil or fat?                                              223
Steam produces greater burns than boiling water. Why?           224
What is the name of the dreaded black mould that
  colonises damp places in bathrooms? Because
  materials produced to remove the mould do not
  seem to work, and nor do household bleaches,
  detergents and solvents, can anyone suggest a 
  remedy other than abrasives?                                  226
What is the difference between bacteria and virus?              227
When there is a light in a certain position, I see
  chromosome-like structures about a metre from my
  eyes. They change shape and move wherever I look.
  What are they and does everyone see them?                     228
Why do finger tips become white and cold when we put
  rubber bands around them?                                     230
Why do eyes produce tears when tear gas is used?                230
How do race organisers time cyclists? If they do it by
  video, how do they get separate times from the 
  hundreds of riders who cross the finishing line
  at the same time?                                             231
What is computer simulation technique?                          232
What are supercomputers?                                        233
Is it true that condensed milk has more fat than ordinary milk? 235
What are artificial teeth made of?                              236
What is an aqualung?                                            237
Why is fire hot?                                                238
How is knocking reduced in vehicles using unleaded petrol?      239
Nickel-cadmium cells used in rechargeable torch lights,
  shavers, etc. are said to have a memory effect.
  What is this memory effect and how does this affect
  the battery performance?                                      240
Does sewage discharge into the sea harm marine life?            242
Why does our hair change its colour as we age?                  244
Why are the wing tips on modern passenger jets upturned?        245
How is honey naturally nutritive? Do all flowers have the 
  same composition?                                             246
How can we test the purity of honey?                            247
Why does a corpse float on water, when a living person
  must exert an effort to stay afloat?                          248
After I take a hot shower and the hot, wet air from the 
  bathroom combines with the cold air from the hall,
  why doesn't it rain in my house?                              248
Why does snow melt faster around a tree trunk?                  249
What is the difference between butter and cheese?               249
While some motor vehicles belch smoke, some are
  very clean without any visible smoke coming out of
  their exhaust. What makes them differ? Is there any
  simple way to control this pollution?                         251
Why do we become unconscious when hit on the head?              252
What is the principle behind breath analysers used to
  detect drunken-driving                                        253
How do we calculate the fat per cent in milk?                   253
Can we use methanol or ethanol bio-fuels in motor vehicles
  and pumpsets? Is it helpful in reducing pollution?            255
Why is fuel used in airplanes different from those used in 
  motor vehicles?                                               255
Why do fingernails grow faster than toenails?                   257
Why is Sriharikota a place suitable for launching rockets?      257
The last time I went to the Empire State Building 
  (in the U.S.), it looked as if the building was swaying. 
  Is this an illusion?                                          259
How does a water diviner work?                                  260
What is the advantage of sucking a cut finger?                  261
What is automatic mail processing unit?                         262
Why is the @ symbol used in an email address?                   263
How does ballast-less track provide safe travel?                264
What is the pH of rainwater? Is the pH suitable
  for drinking?                                                 264
Are the vocal cords of professional singers wired in
  such a manner as to make their voice mellifluous?             265
How do people walking on burning coal not burn their feet?      267
Soaps come in different colours. But why is soap's lather
  always white in colour?                                       267
How is a ventrilouist able to throw his voice                   268
Why do we see rainbow colours on a CD?                          269
Breast-fed babies brainier?                                     271
You are human if you are hairless                               274
The smells of silence                                           277
Leech: the parasite physician                                   281
Life in fire and brimstone                                      283
Who can see well under water? Moken!                            287
Science's top ten achievements of 2001                          291
Top ten achievements during 2002                                298
Top ten breakthroughs of the year 2003                          304
Index                                                           309