The Wei T'o Nonaqueous Book Deacidification System, an in-progress pilot project at the Public Archives of Canada, is presented in terms of institutional background, system selection, characteristics of liquified gas systems, and current system design. The manual aqueous (magnesium bicarbonate) and nonaqueous (magnesium methyl carbonate: magnesium methoxide mixture with carbon dioxide in methanol and trichlorotrifluoroethane) deacidification solutions used at the Public Archives extend potential record life but are limited to unique, valuable records because of treatment cost. The system was chosen as a pilot project test because its chemistry was accepted, a history of successful use existed, and mechanical problems of handling liquified gas solvents appeared solvable. Deacidification of paper using liquified gas solvents to dissolve, carry, and deposit deacidification agents function analagously to chlorofluorocarbon refrigeration cycles. Successful treatment requires vacuum drying books to 0.5% moisture or lower, solution impregnation at pressures up to 200 psig, and flash drying to deposit the deacidification agent throughout the materials treated. See also AATA 15-389.