4 BULLETIN 72, U. S. DEPARTMENT OF AGEICULTUEE. 



little action on the sulphide and the sulphate. During cooking the 

 organic acids produced react with the sodium sulphide^ as well as 

 with the caustic soda, so that in calcining both chemicals are recovered 

 as sodium carbonate. If desired, soda ash may be added to the smelt 

 solution before causticizing in order to increase the proportion of 

 caustic soda in the cookmg liquors. Some mills have also found it 

 advantageous to mix with the causticized cooking liquors some of 

 the black liquors diverted from the recovery operations. 



The soda and sulphate processes can be apphed to extracted or 

 steam-distiUed chips from which rosin and turpentine have been 

 removed. Turpentine can also be obtained from resinous chips 

 durmg the cooking operations by condensing the "rehef" from the 

 top of the digester. However, the turpentine is very impure, and 

 in the case of the sulphate process contains organic sulphur compounds 

 from which it is separated ^dth great difficulty. 



EXPERIMENTAL METHODS. 



KINDS OF TESTS. 



The tests made by the Forest Service were of two classes: (1) Auto- 

 clave tests and (2) semicommercial tests. The autoclave tests com- 

 prised several series of cooks made to determine the effects of varying 

 the cooking conditions of the sulphate process. The semicommer- 

 cial tests include cooks niade by the soda as well as by the sulphate 

 process. The semicommercial sulphate cooks employed such cook- 

 ing conditions as the autoclave tests indicated would give good 

 results, while the tests using the soda process were made with cooking 

 conditions that would give results comparable to those obtained from 

 the sulj)hate cooks. Because the semicommercial tests show in a 

 more direct manner the possibihties of preparing paper pulp from 

 longleaf pine, they will be discussed before the autoclave tests. 



WOOD USED. 



The test material consisted of longleaf pine (Pinus palustris IMill.) 

 from two locahties. Perry Count}^, ^liss. (shipment L-3), and Tangi- 

 pahoa Parish, La. (shipment Lr-176). A portion of the former, con- 

 sisting of edgings containmg approximately equal amounts of sap- 

 wood and heartwood, was used for cooks 176-1, 2, and 3 of the semi- 

 commercial soda tests (Table 3), and another similar portion of the 

 same shipment was used for cooks 1 to 65, inclusive, of the autoclave 

 tests. The average bone-dry weight of the wood used in these auto- 

 clave tests was 30.4 pounds per cubic foot green volume; the maxi- 

 mum and minimum values were 36.4 and 26.6 pounds, respectively. 

 The wood was fairly free from resin. The remaining cooks employed 



> In this reaction volatile organic sulphur compounds having extremely disagreeable odors are produced. 

 Unless these odors are eliminated, or held in check by proper means, sulphate pulp mills are highly objec- 

 tionable except in sparsely populated regions. 



