## Facts

- Linde Air Products Co. owned a patent covering an electric welding process and welding flux compositions using an alkaline earth metal silicate with calcium fluoride.
- Graver Tank & Manufacturing Co. made and sold a competing welding flux.
- The accused flux substituted manganese silicate for the claimed magnesium silicate; manganese silicate was not literally within the patent’s “alkaline earth metal silicate” language.
- Linde sued for infringement, alleging infringement under the doctrine of equivalents despite the literal difference.
- The district court found infringement based largely on expert testimony that the substituted ingredient performed the same role in the flux.
- The court of appeals affirmed.
- The Supreme Court granted review to address whether the substitution avoided infringement and, on rehearing, reaffirmed infringement.

## Issues

1. Whether substituting a chemically different ingredient not within the claim’s literal terms avoids infringement when the substitute performs the same function in substantially the same way to achieve substantially the same result.
2. What considerations govern an equivalence determination for chemical compositions.
3. Whether equivalence is a factual determination warranting deference to the trial court’s findings.

## Decision

- The Supreme Court held that the doctrine of equivalents applies to chemical compositions as well as mechanical devices.
- The Court concluded that replacing magnesium silicate with manganese silicate was, on this record, an insubstantial change.
- The accused flux infringed the patent under the doctrine of equivalents.
- The Court treated equivalence as a question of fact and indicated that trial-level equivalence findings should not be set aside absent clear error.
- Justice Black, joined by Justice Douglas, dissented, criticizing the use of equivalents as expanding patent scope beyond Congress’s scheme.

## Legal Principles

- Patent infringement may be found under the doctrine of equivalents when the accused product or process performs substantially the same function in substantially the same way to obtain substantially the same result, despite nonliteral differences.
- Equivalence analysis considers: the purpose of the ingredient in the claimed invention, its qualities when combined with other ingredients, the function it performs, and whether skilled artisans would have known the ingredients to be interchangeable.
- The doctrine of equivalents is available for chemical compositions and is not confined to mechanical inventions.
- A determination of equivalence is a determination of fact; appellate review of such findings is deferential.

## Conclusion

The Court affirmed infringement where a competitor avoided the claim’s literal language by substituting a different chemical ingredient that operated interchangeably and produced substantially the same results, confirming that equivalence is a fact-driven inquiry applicable to chemical compositions.


Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 339 U.S. 605 (1950)