1.37 gram of cupric oxide on reduction with hydrogen gas gives 1.098gram of copper

This satisfies the law of definite proportion or constant proportion and it can be proven below.

Explanation:

The law of constant or definite proportion states that all pure samples of the same compound no matter how they are made; are made up of the same elements combined in the same proportion by mass. The can be verified by finding the ratio of copper to oxygen in the both experiment listed above.

In the first experiment:

1.37 g of cupric oxide contains 1.098 g copper therefore oxygen = 1.37 − 1.098

=0.272 g

The ratio of copper to oxygen is=

1.098 ÷ 0.272

= 4:1

In the SECOND or next experiment:

1.476 g of cupric oxide contains 1.17 g copper Therefore oxygen = 1.476−1.17

=0.306g

The ratio of copper to oxygen is =

=1.176 ÷ 0.306

=3.8:1

Which is approximately≃4:1.

In conclusion, despite the different methods of the experiments, composition of copper of copper in the two different samples are the same and the cupric oxide obtained from different sources contain the same elements ( copper and oxygen) combined in the SAME ratio.