BULLETIN 80, U. S. DEPAETMENT OF AGEICULTUEE. 
If any one of these conditions be altered and the other two kept constant, the yield 
varies inversely as the altered condition. Thus, in the case of esparto, the author 
performed a series of experiments in which the proportion of caustic to unit weight of 
esparto was varied, whilst the temperature and duration of time of digesting were both 
kept constant with the following results (Table 2) . 
Table 2. — Experiments regarding yield of air-dry bleached pulp from Oran esparto. 
No. of ex- 
periment. 
Esparto, 
weight 
taken. 
Soda liquor. 
Conditions of boiling. 
Weight of 
air-dry 
pulp. 
Dry pulp 
on dry" 
esparto. 
Bleaching 
powder. 
Volume. 
Na 2 0. 
Time. 
Tempera- 
ture. 
Pressure. 
1 
Grams. 
200 
200 
200 
Cc. 
800 
800 
800 
Per cent. 
1.58 
2.13 
2.69 
Hours. 
3 
3 
3 
°C. 
142 
142 
142 
Lbs. 
55 
55 
55 
Grams. 
87.30 
80.67 
72.00 
Per cent. 
43.91 
40.55 
36.20 
Per cent. 
29.5 
2 
18.5 
3 
10.5 
Variable. 
Pressure varied. 
Strength of caustic varied. 
Time varied. 
Note.— The different trials were made in wrought-iron tubes fitted with screw caps, all three being 
heated together in an oil bath for three hours at a temperature of 302° F. (55 pounds above atmosphere). 
The following is taken direct from Cross, Bevan, and Sindall's I 
resume of Beveridge's experimental results, which include the data 
quoted in Table 2 and others: 
He made three sets of trials, as follows: 
Constant conditions. 
1. Time and strength of caustic. 
2. Pressure and time. 
3. Pressure and strength of caustic. 
The results were: 
1. Increase of pressure resulted in a diminution of yield, the quantity of pulp 
obtained being reduced considerably. 
2. Excess of caustic soda caused rapid diminution in the yield of cellulose. 
3. Gradual exhaustion of the caustic soda by prolonged digestion prevented such 
serious diminution of yield. 
The discussions and experimental results which have been quoted 
show in a general way the effects of varying some of the fundamental 
cooking conditions in the soda process. None of the experiments 
cited are directly comparable to commercial practice in this country, 
because the testing conditions were not sufficiently representative of 
manufacturing conditions, and, in the case of Beveridge's experi- 
ments, because esparto — a grass, or pectocellulose — was used as the 
test material. Moreover, the effects of the cooking conditions 
employed were not studied in as great detail as seemed desirable. 
The experiments show very clearly, however, that improper cooking 
conditions are wasteful or inefficient, and indicate the need for com- 
plete experimental data on which improvements in commercial 
practice may be based. 
i Wood Pulp and Its Uses, p. 132, 1911. 
