8 



BULLETIN 72, U. S. DEPARTMENT OP AGRICULTURE. 



treatments are necessary than if the pulps are to be used in natural- 

 color wrapping papers. The present experiments apply more espe- 

 cially to the latter, for which the important properties are strength, 

 toughness, and resistance to wear. The terms mild, medium, and 

 severe cooking, and undercooked, well-cooked, and overcooked pulps 

 used in the following discussion are significant only with respect to 

 the object of the tests. 



MILD COOKING TREATMENTS. 



The less severe the cooking of a wood the larger will be the yield 

 of crude pulp. However, there is a point at which the pulp will begin 

 to lose its valuable properties for making wrapping papers. For cook 

 71 the digesting conditions were outlined to give a much undercooked 

 pulp (see Table 1), but the treatment given the wood was even less 

 severe than is indicated by the recorded data, since a portion of the 

 digester liquor was lost through leakage soon after the cook had been 

 started. The crude unbeaten pulp from this cook was full of soft 

 chips, which, while hard enough to resist the action of a stream of 

 water under pressure, could easily be picked apart with the fingers. 

 The paper made from the beaten pulp had a strength factor of 0.50, 

 was moderately tough, and had fair wearing properties. As a wrap- 

 ping paper it would be considered of medium grade. The yield, 61.2 

 per cent, or 2,172 pounds per solid cord, was very high, considering 

 the quality of pulp obtained. Pulps produced under less severe 

 cooking conditions had higher yields (see autoclave tests, pp. 14-24), 

 but the quality was not so good, as evidenced by brittleness, lack of 

 strength, and poor wearing properties. 



TABLE 1. Record of semicommerdal tests using the sulphate process. 



1 A portion of the digester liquor was lost, due to leaks during the early stages of cooking. 



