4 BULLETIN 72, U. S. DEPARTMENT OF AGRICULTURE. 
little action on the sulphide and the sulphate. During cooking the 
organic acids produced react with the sodium sulphide 1 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 cooking 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 applied to extracted or 
steam-distilled chips from which rosin and turpentine have been 
removed. Turpentine can also be obtained from resinous chips 
during the cooking operations by condensing the "relief" 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 with 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 made 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 sulphate cooks. Because the semicommercial tests show in a 
more direct manner the possibilities 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 Mill.) 
from two localities, Perry County, Miss, (shipment L-3), and Tangi- 
pahoa Parish, La. (shipment L-176). A portion of the former, con- 
sisting of edgings containing 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 
i 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. 
