chips in Expts. 1-7, and on the weight of the origi- 

 nal resinous wood in Expt. 8. 



"Causticity" refers to the ratio of the sodium 

 oxide present in the cooking liquor in the form of 

 NaOH over the total amount present both as 

 NaOH and Na 2 CO 3 . 



The pulp was dried at 105C. and the yield 

 calculated first as percentage of the original re- 

 sinous wood to show the over-all yield, and second 

 as percentage of actual dry rosin-free wood in the 

 original material, to indicate the true efficiency of 

 the pulping operation. 



The turpentine figures refer in the first 7 experi- 

 ments to* the additional recovery during the soda 

 cook, signifying in several cases incomplete dis- 

 integration of the oleoresin in the preliminary 

 treatment. In Expt. 8 the turpentine was obtained 

 by a combined extraction and pulping of the wood. 



The actual data are in many ways not compar- 

 able with those in ordinary soda-mill practice. 

 The "liquor /wood" ratio is usually from 4 to 6, 

 when a digester is filled with chips and flooded 

 with liquor. Because of the decreased volume of 

 the wood after preliminary extraction, a larger 

 ratio of cooking solution was necessary to properly 

 fill the experimental digester and prevent exposure 

 of the chips. With lean woods the "Na 2 O /wood" is 

 usually from 17 to 25 per cent and the actual 

 consumption of NaOH about 20 per cent, equiva- 

 lent to about 15 per cent of Na^O. By reason of 

 the partial attack of the lignin in the preliminary 

 extraction, a ratio of sodium oxide below 20 per 

 cent was found to be most satisfactory. The 

 above considerations necessitated a low strength of 

 cooking liquor lower than .would be necessary in 

 practice. A concentration of 5-10 per cent NaOH 

 is usually employed in practice. 



The pressures used in soda cooking vary from 

 75 to 150 pounds, the higher values applying 

 particularly to deciduous woods, such as poplar and 

 basswood. In these experiments a pressure of 

 100 pounds was chosen as a satisfactory figure for 

 pine. The time necessary to reduce the pine to 

 pulp was comparatively short due to partial de- 



47 



