Kohsai Udagawa (1821-1887) was one of scientists in Japan. He lived from the last days of the Tokugawa shogunate to the early days of the Meiji era. Present paper is about interpretation of his manuscript concerning Niepceotype albumen wet plate photography, named "Potokarahii" and the results of experiment on the process. It was supposed that the old document was a translation from a Dutch technical book. It contains preparation and image formation on a silver iodide-albumen photosensitive layer on a glass plate. It consists of following items ; introduction, cleaning of glass plate, preparation and coating of iodide-albumen solution, sensitization, light exposure, development, fixing, washing and drying. Interpretation was a little difficult, because the manuscript was composed of classical Chinese characters. "hentai-kana", classical Japanese character, and old Dutch technical terms and units. Sentitometric exposure of plates was operated in the way of time scale, because a light wedge could not be contact with the wet surface of plates.ISO photographic speed calculated from the results of 5500 K sensitometry was equivalent to 4 × 10^, although effective speed was about ten times faster in taking picture as is mentioned in the later part of the abstract. Development time was shortened by treatment with saturated gallic acid solution before light exposure. Solarization of image appeared in the higher exposure region without the treatment. In addition to them, it was desired to add silver nitrate solution into a gallic acid developer to obtain a negative image having proper density on the plate. Spectral response was observed in the region of 330 nm-500 nm with maximum sensitivity at 400 nm. Effective speed of the plate was 4 × 10^ in taking picture, owing to the sensitivity to ultra violet and blue rays. It took 10-15 minites at F numbers of 8-11 to take portrait or still life in the open air. Some consideration was made for the reason why "Potokarahii" was not published in those days
