I am not able to understand law os reciprocal proportions please define it in a even simpler language.

This law states that ‘when two elements combine separately with third element and form different types of molecules, their combining ratio is directly reciprocated if they combine directly.”

The above law is the basis of law of equivalent masses, which will be described latter in details.

For example:

ratio of masses of carbon and sulphur which combine with fixed mass (32 parts) of oxygen is

12:32 or 3:8                                  …(1)

Inratio of masses of carbon and sulphur is

12:64 or 3:16                     …(2)

The two ratios (1) and (2) are related to each other by 2:1

or  

i.e. first ratio is integral multiple of second.