PRODUCING SODA PULP FROM ASPEN. 9 



METHOD OF CONDUCTING EXPERIMENTS. 



SCOPE AND PLAN OF TESTS. 



Aside from the character of a wood or other material prepared for 

 cooking, the principal cooking conditions affecting yields and proper- 

 ties of pulps, consumption of cooking chemicals, and the general 

 efficiency and costs of the cooking operations are indicated under 

 the following general headings : 



(1) Preliminary treatments which may in some cases be given the prepared 



chips. This includes such treatments as preliminary pressure, vacuum, or 

 steaming. 



(2) Character of the cooking apparatus, including size, shape, and construction 



of the digester; manner of heating, whether by saturated or superheated 

 steam turned directly into the digester, or by the use of steam jackets or 

 flue gases; also the degree and kind of mechanical agitation employed, 

 if any. 



(3) Proportions of the charges. This covers the amounts of wood and chemicals; 



also the amounts of water present in the wood and the original cooking solu- 

 tions together with the water condensing in the charges from steam used in 

 - cooking. 



(4) Character of the cooking liquors when charged. Such items as causticity, 



initial temperature, impurities, and concentration are important. 



(5) Duration of the cooking treatment. The treatment is in three periods — (a) a 



period of increasing temperature; (b) a period at maximum temperature; 

 and (c) in some cases, a period of decreasing temperature. 



(6) Pressures and temperatures. This considers the pressures and temperatures 



of the digester contents at different stages of cooking; also the tempera- 

 ture of the digester room (as affecting radiation and condensation). 



(7) Manner of admitting steam, "relieving," and "blowing" the digester. 



Since the effects of the variable cooking conditions may be modi- 

 fied by the treatments given the pulps after leaving the digester — 

 such as leaching or washing, screening and bleaching — these treat- 

 ments must also be taken into account, for it is not possible to de- 

 termine all the important effects of the cooking treatments until the 

 finished pulps have been prepared. 



The many factors are more or less interdependent, and any change 

 in one results in unavoidable changes in others. Four of the more 

 fundamental of these factors have been investigated in the Forest 

 Service experiments. They are: 



(1) Amount of caustic soda charged per pound of wood. 



(2) Duration of cooking at maximum temperature. 



(3) Maximum temperature (pressure) of cooking. 



(4) Initial concentration of the cooking chemicals. 



The effect of these four factors upon the yield and properties of the 

 pulp and the consumption of cooking chemicals were determined. 1 



1 The purely chemical aspect of the cooking action has not been given special consideration. The effect 

 of the caustic soda cooking liquors under the conditions employed in pulp making is recognized as a hydro- 

 lytic action in which the caustic soda extends the limits of hydrolysis. This subject has been given care- 

 ful attention by Cross and Bevan, Schwalbe, De Cew, and others as indicated in previous references. The 

 effects of the cooking conditions on the recovery of soda also have been given no consideration except in a 

 very cursory manner. The laboratory facilities did not permit this important subject to be studied at the 

 time of the experiments. 



