Question
Show that the law of reciprocal proportions is proved by the following results:
1·4g of the element A is known to combine with 1·6g of element B, while 0·5g of another element C combines with 3·5g of the element A and 2·857g of the element C combines with 22·857g of element B.
Solution
(i) In AB compound:
1.4 g of A combines with 1.6g of B
1 g of A combines with 
(ii) For AC compound:
3.5 g of A combines with 0.5g of C
1g of A combines with 
Ratio of masses of B (in AB) and C(in AC) that combines with the fixed mass of A(1 g) is
(iii) In BC compound:
Ratio of masses of B and C, when they combine to form BC is
Since the two ratios (1) and (2) between the masses of B and C are same, hence the law of reciprocal proportion is proved.
