Stephen Johnson Field

“ Where a useful result is produced in any art, manufacture, or composition of matter by the use of certain means for which the inventor or discoverer obtains a patent, it is, as justly observed by the presiding justice of the Circuit Court, too plain for argument, that the means described must be the essential and absolutely necessary means, and not mere adjuncts which may be used or abandoned at pleasure. ”

“ The change made in the old specification, by eliminating the necessity of using the fat liquor in a heated condition, and making in the new specification its use in that condition a mere matter of convenience, and the insertion of an independent claim for the use of fat liquor in the treatment of leather generally, operated to enlarge the character and scope of the invention. The evident object of the patentee in seeking a reissue was not to correct any defects in specification or claim, but to change both, and thus obtain, in fact, a patent for a different invention. ”

“ The state of the liquor is not mentioned as essential to the treatment, or to accomplish any of the results sought. It is only stated as a thing to be desired, that the liquor should be heated, and that it would be preferable that other ingredients were mixed with the heated liquor to make the compound mentioned. ”