of unbleached kraft pulp sandwiched between two sheets of commercial paper containing 20 calcium carbonate all sheets in any given pile had previously been conditioned at a certain humidity and this humidity was maintained by confining each pile to a sealed plastic bag the piles were then pressed at 1 psi at various times sheets were removed from the piles and were titrated by the procedure already described the original acid content was 46 meq kg and fig1 shows in a quantitative manner the fraction to which this acid content was reduced at various humidities the rate of deacidification is slow at 50 a barely resolvable decrease in acid content being observed in 30 days the rate is however increased as the humidity is raised especially to humidities in excess of 75 at 97 rh the residual acid content was 10 after 15 days and 0 after 40 days piles of sheets were constructed as described in the previous example except that the humidity of all piles was 97 and the pressure was varied from pile to pile within the range of 0 01 to 50 psi the rate of deacidification was evaluated as in the previous example and found to be very dependent on pressure the results are shown in fig2 the original acid content of 46 meq kg was reduced to 10 of this value after 2 days at 50 psi after 10 days at 10psi and after 15 days at 1 psi.