Graver Tank v. Linde Air Products Co.
339 U.S. 605 (1950)
Linde invented a welding
process and received a patent on it. Linde sued Graver for infringement for using a very similar process.
Graver argued that it wasn't
the same process at all. Sure, 99% of the process was identical, but
where the Linde patent specified a welding compound that consisted of
calcium and magnesium, the Graver process used calcium and manganese.
For all you non-chemists
out there, magnesium and manganese are both elements on the period table
that have similar, but not identical properties.
The Trial Court found for
Linde. Graver appealed.
The Trial Court found that
even though the Linde patent did not claim manganese, it was close enough
that it met the standard of non-textual infringement (aka the Doctrine of Equivalents).
The Appellate Court affirmed.
The US Supreme Court affirmed.
The US Supreme Court found
that the Graver process infringed on the Linde patent via the Doctrine
The Court found that there
are two tests that courts could use to determine non-textual
Under the triple
identity test something is
It performs substantially
the same function,
in substantially the same
to yield substantially the
Under the insubstantial
change test, something is equivalent
if there is only an insubstantial chance between each of the features of
the accused device or process and the patent claim.
The Court found that the
substitution of magnesium for manganese was obvious to anyone working in the field, and was an insubstantial
In a dissent it was argued
that the courts should not expand the scope of the patent beyond what the
USPTO had determined.
In the dissent's opinion, if
Linde failed to claimed manganese, it was their own fault for messing up
their claims. There was nothing stopping them from claiming manganese.
Note that the Doctrine of
Equivalents is a common law doctrine
that doesn't have a statutory basis. It was developed because courts
understood that an infringer wouldn't be dumb enough to copy an invention
exactly, they would make a minor change here or there so they didn't
literally infringe on the patent.