14 BULLETIN 
The soda papers were inferior to the sulphate papers in resistance 
to wear; the latter could be rubbed and crumpled for a long time 
without showing signs of wear, while the former had a tendency to 
become fuzzy and tear under similar treatment. Even those sul- 
phate pulps at very high yields had wearing qualities equal to the 
best soda pulps. There is little doubt that higher yields of good 
kraft pulp can be obtained with the sulphate process than with the 
soda process. Sulphate pulps of fairly good quality can be obtained 
with yields as high as 61 per cent, while the limit for soda pulps is 
approximately 50 per cent. With higher yields the soda pulps lose 
strength and toughness and become brittle. A sulphate pulp with a 
60 per cent yield can be made into a medium grade of kraft wrapping 
paper, while a soda pulp having the same yield will produce only a 
very inferior grade. Considering bursting strength alone, equally 
strong papers can be made by either process. 
The main advantage of the sulphate process over the soda process 
is that in the former the pulp can be very much undercooked and 
still produce a fair quality of paper, while a soda pulp must be com- 
paratively well cooked before a good paper can be made from it. 
Moreover, the best sulphate kraft pulps were obtained with a total 
duration of cooking of only 3.5 hours, while in the soda tests 6 hours 
were required to secure the best results. 
AUTOCLAVE TESTS. 
The autoclave tests, which, as previously explained, preceded the 
semicommercial tests, were made to determine the effects of varying 
the cooking conditions in the production of sulphate pulp. The 
cooking conditions investigated were: 
(1) Amounts of the various cooking chemical employed. 
(2) Cooking pressures or temperatures. 
(3) Durations of cooking. 
(4) Initial concentrations of chemicals in the digester liquors. 
Aside from the chemicals normally present in sulphate cooking 
liquors — that is, caustic soda, sodium sulphide, sodium sulphate, and 
sodium carbonate, the effects of sodium chloride and sulphur in con- 
junction with caustic soda were studied. The tests, Tables 4 to 
10, inclusive, were made in series, in any of which all cooking con- 
ditions except the one under observation were held as nearly constant 
as possible. 
The amounts of sodium carbonate and of S0 2 compounds expressed 
as Na 2 S0 3 in the cooking liquors were in general small and no 
mention of them is made in the tabulated data. The amounts of 
sodium sulphate present are indicated only relatively, except in 
Tables 6 and 10. 
