Law of Multiple Proportions Definition - Chemistry Glossary

Sample being pipetted into test tubes during a laboratory experiment
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by Anne Marie Helmenstine, Ph.D.
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
Updated February 04, 2019

The Law of Multiple Proportions states that when elements combine, they do so in the ratio of small whole numbers (assuming they have the same type of chemical bonds).

Also Known As: Dalton's Law, though that term usually refers to his law of partial pressure

Examples: carbon and oxygen react to form CO or CO2, but not CO1.6