John Dalton didn't actually conduct a single experiment to create the law of multiple proportions. He formulated the law based on the work of other scientists and his own observations.

Here's how it worked:

1. Previous work: Scientists like Joseph Proust had already established the law of definite proportions, which stated that a given chemical compound always contains the same elements in the same proportions by mass.

2. Dalton's observations: Dalton observed that some elements could combine in different ratios to form different compounds. For example, carbon and oxygen could combine to form both carbon monoxide (CO) and carbon dioxide (CO₂).

3. Formulating the law: By comparing the ratios of elements in different compounds, Dalton realized that the masses of one element that combine with a fixed mass of another element are always in simple whole-number ratios. This became known as the law of multiple proportions.

4. Example: In carbon monoxide (CO), 12 grams of carbon combine with 16 grams of oxygen. In carbon dioxide (CO₂), 12 grams of carbon combine with 32 grams of oxygen. The ratio of oxygen masses in the two compounds is 16:32, which simplifies to 1:2.

Therefore, the "experiment" was more of an observation and analysis of existing data. Dalton used his atomic theory to explain the law of multiple proportions, stating that it was a result of elements combining in different whole-number ratios of atoms. This paved the way for our understanding of chemical reactions and the composition of matter.