Ask Uncle Pai — Why is the colour of milk white?

We have heard of sound-proof material. Can we have things that are smell-proof too?
— Milind Kulkarni, Pune

We smell a substance or perfume because of the molecules of that substance, dispersed in the air. If an impervious cloth is made, that will not permit the molecules to cross to the other side, we can have smell-proof cloth. If it is treated with wax, perhaps it could be smell proof.

Why is milk white in colour?
— Shweta Bhendigeri, Powai

Milk is basically an emulsion of fat in water. Fill a test tube with a little water. Add a few drops of oil. The water and the oil will not mix. Now add a few drops of soap solution. Shake the test tube. You will find a whitish solution that is an emulsion of oil in water. Milk is like that. When salt is put in water, you get a solution of salt in water. The identity of the salt is completely lost in the water. In an emulsion, the oil or fat does not lose its identity, but gets broken into a very small globules in the solvent (water in the case of milk).

Q: How does poison kill?
— Seema,Uran

There are different types poisons that work in different ways. It is therefore difficult to answer this question. For example, potassium cyanide immediately attaches itself to haemoglobin in the blood which is the carrier of oxygen. So, the oxygen cannot be carried to the vital parts of the body, as a result of which a person dies.Carbon monoxide also acts in a similar way. Haemoglobin has a greater affinity for carbon monoxide than for oxygen. Together they form a stable compound. As a result enough haemoglobin would not be available to carry oxygen to the various parts of the body and life becomes impossible in the absence of oxygen.