18 BULLETIN 72, U. S. DEPARTMENT OF AGRICULTURE. 
the maximum gauge pressure was 100 pounds per square inch. The 
product came from the autoclave in the form of hard, black chips 
which were quite "raw" on the inside; the yield was not determined. 
In comparison with this result, cook 40 (Table 6), using, per 100 
pounds of wood, 10 pounds of caustic soda, 5 pounds of sodium sul- 
phide, and 5 pounds of sodium sulphate (the latter being of no 
assistance in cooking), also afforded a product in the chip form. 
These chips, however, were soft, and could easily be picked apart with 
the fingers. Of the 3 hours' totalduration for this cook, 2.3 hours 
were at a maximum pressure of 90 pounds. The yield was 65.7 per 
cent. While it is hardly safe to base a general conclusion upon a single 
trial, this test indicates that sodium carbonate, at least when present 
in considerable quantity, retards or diminishes the effects of the 
caustic soda and sodium sulphide. 
EFFECTS OF SODIUM SULPHATE. 
Sodium sulphate is present in the commercial cooking liquors, due 
to incomplete reduction of the sulphate to sulphide during the smelt- 
ing operations. Like sodium carbonate, it is of practically no assist- 
ance in cooking. A cook of 3 hours' duration and 90 pounds maxi- 
mum gauge pressure was made, using sodium sulphate in the propor- 
tion of 50 pounds per 100 pounds of wood, which yielded 86.3 per cent, 
while another cook of the same duration and pressure but without 
any chemicals whatever (that is, using pure water alone) had a yield 
of 89.1 per cent. Allowing for experimental errors, there was little 
difference between the results of these two cooks, and in neither case 
could the product be beaten into pulp. 
A cook was also made, using 40 pounds of sodium sulphate, 10 
pounds of caustic soda, 5 pounds of sodium carbonate, and 5 pounds 
of sodium sulphide per 100 pounds of wood; the duration was eight 
hours and the maximum gauge pressure was 100 pounds per square 
inch. Only hard black chips were obtained, of no value whatever 
for pulp. As in the case of the sodium carbonate, there is an indica- 
tion that sodium sulphate retards the action of the other chemicals. 
To prove this further tests are necessary. 
EFFECTS OF VARYING ALL CHEMICALS IN SAME PROPORTION. 
A series of tests was made varying the amounts of all sodium com- 
pounds present in sulphate cooking liquors. The several constituents 
were kept constant in regard to each other in the proportion of 50 
parts caustic soda, 25 parts sodium sulphide, and 25 parts sodium 
sulphate. For convenience the amounts of the different chemicals 
have been computed to a common basis, and the combined values are 
expressed as Xa 2 (sodium oxide). 
