US Patent No. 41,825, granted March 8, 1864 to George W. Billings of New York, for an improved method of retting flax and hemp straw. The specification describes a steam-heated vat in which upright stalks are immersed in stages, in thirds, at 85-90°F. This is meant to give uniform loosening of the fiber from the woody stem. The patent includes a drawing of the vat in cross-section and a single claim.