9 . f 2321 3
U. S. Department of Agriculture, Forest Servic e
FOREST PRODUCTS LABORATOR Y
In cooperation with the University of Wisconsin
MADISON, WISCONSI N
CHEMISTRY OF THE SULPHITE PROCES S
II. Chemical Properties of - Pulps Prepared By Indirect Coi+rl'i gt
By MARK W . BRA Y
Chemist in Forest Products
an d
T . M . ANDREW S
Associate Chemist in Forest Products ,
Published i n
PAPER TRADE JOURNAL
January 18, 192 3
Vol LXXVI, No .' 3 .
Reprinted in Pap er trade journal, January 18, 192 3
CHEMISTRY OF THE SULPHITE PROCES S
El,. Chemical Properties of Pulps Prepared by Indiredt Cooking '
This study of sulphite pulp was undertaken in order to deter mine the nature of product obtained with different periods of cookin g
and to show, if possible, the factors influencing the character of th e
product at various stages of the reaction . Such an investigation i s
possible only by following the process at regular stages from the ra w
condition to the end of the cook . With this end in view a detaile d
chemical study was made of pulps at definite intervals of cooking, al l
conditions of temperature and pressure being maintained as closely a s
possible on a standard curve .
Met a
s of an l_ysi s
Considerable dLfticulty has been experi , eced in finding a
dependable method of analysis for pulps . A modified. Coss and Bevan
method has proved most satisiactory for the determination of the cellulose content . The alpha-, beta-, And gamma-celluloses were
g
determine d
.
Certai
n
by the method developed at the Forest Products Laboratory
pulps especially the raw cooks, appear to be oxidized by the chlorin e
1
2
Presented at the fall meeting of the Technical A .ssociation of the Pul p
and Paper In d ustry at Detroit, r'ich ., October 9 and 10, 1922 .
Chemist in forest products, Forest Products L a b oratory, Madison, Wisconsin .
3Associate chemist in forest p roducts, Forest Products Laboratory, Vadison ,
Wisconsin .
4
1 . w. Schorger, J . Ind . Eng . Chem ., Vol . 9, p . 556 (1917 )
5
An Improved Method for the Determination of Alpha-, Bota-, and Gamma Cellulose . Presented by the authors at the sixty-fourth meetin g
A . C . S . (September, 1922) .
R47
treatment and hence give a corres p ondingly high solubility in the [ercer' s
solution (17 .5 p er cent YaOH) used. in the separation of the stable alpha cellulose from the unstable beta-, and gamma-celluloses . However, by careful manip ulation this oxidation can largely be avoided, in most instances .
The moisture, hot-water-soluble, and lignin contgnts have been determine d
by the ordinary methods used at this laboratory .
E merimentalivitsche_rlich Sul phite Cook s
The pulps used in the investi gations were made in a 50-poun d
capacity digester at the Forest Products Laboratory, thereby permittin g
the cooking conditions to be observed in detail . 7 The various factors o f
pressure, temperature curve, strength of cooking acid, both free an d
combined S 2 are that furnished . These conditions combined with a detailed chemical study i:urr:J.oh a basis for determining the relation of pulp s
of this series and show the way to a new and im p roved series of cooks .
As it is impossible to obtain representative samples of pulp s
during the process of coeki .ng, cooks were blown at definite periods fro m
the raw stage to a well-coobred product . All these cooks followed a s
nearly as possible the ware curve, p ermitting the data from the separat e
cooks to be a pp lied at any similar period durin_e a single cook .
•
The spr, , ce woad used in these melee analyzed 53 .4 p er cen t
Cross and Bevan cellulose an . 7 4 .7 per cent aapgin,-, 5 .7 per cent beta- ,
and 14 .2 per cent mamma-cell"ioeo, ac shown in Tdhle 1 . As would b e
exeected_, the hat-water sole 'le and the 1 eel- cent sodium hydroxid e
soluble contents are considerable amounts, which taken with a ligni n
content of 2 8 . per cent partly account for there being only 58 .4 pe r
cent cellulose as determined by the Cross and Bevan method . Yet eve r
this yield is not equaled in commercial cooking . With the result s
of the different cooks it is possible, perhaps, to show some of th e
causes, or at least the stages, of the disintegration or changes tha t
wood undergoes during continued treatment with hot sulphite cookin g
liquors .
6
7
S . A . Yarood and D . E . Cable, J . Ind . Eng . Chem ., Vol . 14, No . 8, pag e
727 (August, 1922) .
Cooking data supplied by R . Y . miller and W . F . Swanson, Paper Trad e
Journal, April 13, 1922 . Technical Association Paper Series V (1922) ,
pp . 69-74 .
R47
TABLE 1-ANALYSIS OF EXPERIMENTAL MITSCHERLICH SULPHIT E PULP S
Basis of Wood
Cook
No.
Spruce wood
Sample
No
52 . . . . . . . . . . . . . . . . . . . .
630-I
51 . . . . . . . . . . . . . . . . . . . . . . 629.1
44 . . . . . . . . . . . . . . . . . . . . . 626-I
37 . . . . . . . . . . . . . . . . . . . . . . 625-I
63 . . . . . . . . . . . . . . . . . . . . . . 634-I
62 . . . . . . . . . . . . . . . . . . . . . . 633 .1
53 . . . . . . . . . . . . . . . . . . . . . . 631-1
61
69
. . . . . . . . . . . . . . . . . . . . ..
. . . . . . . . . . . . . . . . . . . .. .
632-I
636-I
Cook
duration
Hrs,
Hot
Water
Sol .
%
5.6
5.1
2.2
Yield
%
7
9
10
80 .8
62.8
64 .0
51 . 0
5 0.6
1134
12
1 .9
0.6
0.5
0.0
51 .2
1234
1331
51 .6
47 .1
48 .4
15
0 .8
0.2
1%
NaOH
Sol
1%NaOH Sol.
Corrected for
Water Sol . Lignin
15.1
9 .5
9 .7
9.1
6 .5
6.7
5 .3
14 .8
11 .2
8.4
7 .3
5 .7
5.6
5 .9
5 .3
5 .3
28.3
20.9
12.0
10.6
3 .9
4.6
3.8
2.5
5 .1
5 .9
4.5
28 .4
35.8
36 .7
38 .5
37 .3
46 .7
42 .7
43.1
Sample
No
52
51
44
63
37
62
53
61
69
. . . . . . . . . . . . . . . . . . . . ..
. . . . . . . . . . . . . .. .
. . . . . . . . . . . . . . . . . . . .. .
.
. .
. . . . . . . . . . . . . . . . ..
. . . . . . . . . . . . . . . . . . . .. .
Chips
Cook
No.
oven
dry
630-1
629-I
626-I
625-I
Lbs.
101.6
634-1
633-I
631-I
632-I
636-I
97.5
90.6
92 .3
98.9
99 .0
102.0
95 .9
88.3
Cook
No .
630-I
629-1
626-1
633-I
634 .1
633-I
631-I
632-I
636-1
H O
in chip s
Gal.
3.4 0
3 .3 0
3 .08
3 .1 8
3.3 3
3 .3 6
3 .48
3 .24
.3.28
cooking
Hrs.,
7
9
10
11
1135
Moisture
%
2 .4
3 .3
5 .1
4 .1
5.1
1234
0.9
2.9
2 .6
2 .3
40.0
37 .5
36 .9
1 .5
Basis of Cellulose
15
Hot
Water
Sol .
%
6.3
3.5
2.9
1 .2
0.9
00
7
4.9
5 .1
1354
%
14. 2
8. 9
6. 5
6. 2
4. 7
4. 4
5. 5
5. 2
4. 3
5. 0
2.4
Basis of Pulp
Time of
cellulose
%
5.7
8.3
9.7
7.7
31 .7
45 .1
Gamma-
cellulose
%
34 .7
44.2
0.9
Beta-
cellulose
43 .7
3.0
5 .1
Alpha-
Cellulose
%
58.4
50 .2
45.9
45.2
1 .7
0.7
1%
Ns OH
Sol.
%
18 .3
17 .9
13 .1
14 .3
11 .2
10 .9
11 .8
11 .1
12 .7
1% NaOH Sol .
Corrected for
Water Sol.
Lignin
%
11 .9
25.9
14 .4
19.1
10.2
16.6
13.1
7 .6
9.1
10.4
9.9
7.4
11 .8
5.1
9 .4
6.3
12 .0
1 .8
Beta-
Alphacellulose
Cellulose
%
62 .0
%
63 .2
61 .8
71 .9
83.9
87 .2
82 .6
83 .6
87 .7
86 .8
73.1
76 .9
35 .8
87.4
87,9
92.7
89 .9
94.4
1
Gamma-
cellulose
cellulos e
16 .5
21 .1
17. 9
14. 3
12.5
%
15.6
5,5
1 .9
6 .4
5.4
5 .4
2.8
%
10.8
10. 0
12. 2
10. 9
10. 1
11 . 0
TABLE 2-COOKING DATA FOR EXPERIMENTAL PULP S
Cooking
Max- Time to
Bleach
liquor per imam maximum
Cook
Yield of Yield of Yield of
I00 lb. O . D . temComb unsereened screen- screened 35% availterndunTotal
Free
able chlorine
Acid
woad
perature perature
lion
SO,
SOs
pulp
ing
pulp
SOa
Gal.
Gal .
°C .
Hrs.
Hrs.
%
%
%
59.5
Not bleached
61 .9
133
7
7
3 .78
2.37
1 .4 1
80.8 Nit screened 80.8
57 .0
62 .2
145
834
9
3.82
2.42
1 .4 0
62.8 Not screened 62 .8 Not bleached
55 .0
64 .9
145
L36
1 .38
64.0
0.70
63 .3
Over 30
834
10
3 .74
Over 30
57.0
65 .1
145
854
11
3 .81
2 .40
1 .4 1
51 .0
0.70
50.3
.0
2
.58
1
.08
49
.5
Over 30
57
61 .0
145
835
1195
3.80
2.38
1 .4
50
57 .5
61 .5
145
3.79
2.39
1 .42
51 .20
0 .00
51 .2
Over 30
834
12
50.4
Over 30
56 .5
58 .8
145
834
1234
3 .82
2.42
1 .4 0
51 .60
1.20
58 .25
64a
145
2.41
1 .4 1
47 .05
0.75
46.3
Over 3 0
8$4
1 334
3 .82
0 .13
48.3
1S
58 .5
70.0
137
15
15
5.60
4.46
1 .1 4
48 .43
TABLE 3-PHYSICAL TESTS OF EXPERIMENTAL PULP S
Ball Mil l
Machine Run
•
Cook
No .
630.I
629-I
628 .1
624-I
634-1
633 . 1
631 .1
632-I
636-I
Strengt h
Weight Mullen
factor
per
test
points
ream
Llu.
Lbs.
Lbs.
sq. in .
per ream
. . . . . . . . . . . Pulp raw-not tested
. . . . . . . . . . . Pulp raw-mot teste d
56 .6
32 .2
0.5 7
. . . . . . . . . . . 51 .9
46 .8
0 .90
.. . .. .. .. .. .. .. .. .. .. 51 .0
36 .1
0 .72
35 .9
0.76
47 .0
. . . . . . . . . . 46 .0
28 .5
0 .62
. . . . . . . . . . . 48.1
34 .9
0 .72
. . . . . . . . . . . 53 .8
40 .0
0 .74
Tempera.
Breaking
length
Stretch
%
5 , 960
6 ,41 0
1 .7
Meters
2.1
2.7
6,030
5,450
5,830
6,080
6,120
2.1
1.8
2.1
2.5
Double
folds
No .
58
389
271
426
223
363
283
Humid -
tore of
ity of
testteatin$ room ing room
F.
%
65
69
66
71
64 .5
65.0
65 .5
65 .0
68
70
65 .6
65 .0
81
Max-
Time
imum to max.
strength strength
Lbs. sq . in . Min.
65 .0
119
109
80
60
99
109
98
85
95
60
60
60
60
60
Tear .
ing
force
Time
to max.
tear
Min .
1 .5
2.3
40
40
20
40
1,030
730
20
1,500
1 .220
Lba.
1 .8
2.2
1 .9
2,5
1 .8
40
80
Double
folds
No.
670
700
910
Time t o
minimum
fold s
Min .
60
40
40
60
80
40
40
TABLE 5-COMMERCIAL MITSCHERLICH PULP S
Res:rd
No .
P176
P188
P206
P187
P18S
P186
P213
P207
P175
Moisture
Description of wood used
%
Unbleached spruce and balsam
4 .9
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 .5
Unbleached spruce and balsam _ . . 4 .5
Unbleached spruce
Unbleached spruce
Unbleached spruce
Unbleached hemlock
Bleschei spruce snd balsam
Bleached spruce and balsam
4 .3
4 .4
3 .3
4 .3
3,9
4 .6
Hot
H,O
1%
NaOH
%
0 .9
1 .6
0 .6
1,2
0.6
%
10 .5
12.5
12 .4
soluble
1 .7
0.5
0.5
0.0
soluble
11 .4
9 .8
12 .7
14,2
13 .9
11 .6
1% HaOf i
sot . corrected
far water sal .
%
9.6
10.9
11 .8
10.2
Lignin
Cellulose
Alphacellulose
%
L6
5.2
%
%
96 .1
13.7
7 .C
6.2
7.8
1 .4
95 .3
95 .3
94 .6
94.8
90.8
92.4
11 .6
0,5
97.1
9.2
ILO
13.4
1 .3
0.9
98.4
R2 .1
82 .8
86.6
82.2
92.8
83.7
83.8
84.5
81.4
Betacellulose
%
3 .2
5 .1
2.1
3 .4
3 .2
1 .4
3.3
4.1
3 .6
Gamma .
cellulose
%
13. 8
14 . 1
12. 7
13 .9
13. 8
13. 7
13 . 9
11 . 6
13 .2
Yield and Quality of Pulp s
The shorter cooks of this series naturally were raw and afforde d
samples of pulp well without the range of mill conditions as far as rea l
pulp is concerned . Those samples obtained between the seventh and nint h
hours showed a gradual pulping action, but it was not until ten hours o f
cooking that a pulp was obtained that could be screened and made int o
sheets . All the cooking data, such as temperature, t-i,R . .of cooking ,
strength of acid, free and combined, yield, bleaching qualities, an d
machine-run and ball-mill tests are g iven in Tables 2 and 3 . The elevenhour cook had good strength and color and though not of as high qualit y
as good commercial 1,itscherlich pulp was the best product obtained i n
this series ,
Cooking -ith Tecreased Strength of Acid at Decre .sed Ten .eratur e
In order to sec-are for chemical study an experimental pulp whic h
had physical properties more nearly identical with those of commercia l
Mitscherlich pulp a cook was made under conditions somewhat modified fro m
those used in the series . The free 80 2 was increased to 4 .46 per cen t
and the cooking time to 15 hours, while the maximum temperature wa s
reduced to 1370 0, ilade these conditions the yield of p ulp was 48, 4
per cent, based on the d_~y we i ght of the wood_ . This pulp compared favor ably with the eleven--ho,h cook of the series in physical properties, wa s
more readily bleached, aad closely resembled Mitscherlich pulp .
Discus -i.on. of Analytical Della
In Table 1 are given the chemies3 data for this series of cooks .
The curves for yield, cellulose, alpha-, beta-, and gamma-celluloses ,
lignin and 1 per cent sodium hydroxide soluble are show in Figure 1 .
It appears that during the early part of the cook there is a removal o r
destruction of nearly equal parts by weight of cellulose and lignin .
With awns" itewr* of treatment these losses are 8„2 and 7 .4 per cen t
(based on weight of wood.1, respectively, as shown in Table 4 . Durin g
the remainder of the cooking period the lignin loss becomes larger tha n
that of cellulose and the above ratio is not maintained . However, th e
ratio of lignin lost to cellulose lost ran g es from 1 .60 to 2 .17, or a n
average of 1 .77 . This value holes over a range of time from eleven t o
fifteo]a hours ; and the va ric+ ;^ .. from the mean is 0 .11, with the exception of the one instance where it varies 0 .4 . Those results are substantiated by three other series of cooks by the alkaline p rocess, a
full discussion of which will be given in a subsequent publication .
This would indicate that by none of the present commercial methods o f
cooking is i,t possible to obtain a higher yield than approximately 45 pe r
R47
-3-
T-
T
7 .-
. ..Ll
_,_
t
_
r.
I
k-:1 0
.4
-
`
!
ft- -
tr *
w4-1
I
-.
-- -
4-4-
1- --A-
if
;I
.--
41- . 10
- ----
- -
-'- -
-
4!
P
-th l
Ob
-
i
I
L.
.._
p.
I
r
1
I1
._~'-
"
i
_
..
I.
_1
v_
vi
:i
- .. -
..
41
--I-
i
--I/
1
t
_1 .4
_fl
i
I -
i
.L_
---I-r----I
i
it
*
I
-1
S
.
---f-
-Tv.
- -
-1- - 1
-..: .
1,
11
L, ;
-t - -
-kr I
., ,c.
--I-
!
1
__
i
,
-.-,
‘4
'-i
I)
II--
-.I ,
L
■.
•Z,
cent of cellulose as nnlp, although the rood contains annroxirnatel y
scent cellulose .
Since the cookin g conditions in this series are constant, tim e
being the only variable, it is to be expected that the quality of the pul p
will steadily app roach a ma rimnm, while the lignin content will graduall y
tend toward a rinimum . In the seven-hoar cook, which was very raw, th e
yield is very high and only a small part of the . lignin has been removed .
Compared with the cellulose based on bone-dry wood there is a loss o f
8 .2 per cent cell"lose in this period of cooking . An additional two hours
of cooking removes 8 .9 per cent li g nin with an adr'i.tional loss of. 4 .8 :-p e r
cent in cellulose material . The next two hours a ppear to cause the greatest change in the ;nature of the pulp both physically and chemically .
Mtn the ninth hour of cooking the cellulose percentage in th e
pulp has increased but slightly .
From the eighth to the eleventh hou r
this value in the p ulp increases 25 .7 per cent to 8 .8 per cent with a
lignin content of 7 .6 per cent . However, the yield of cell„lc .ee materia l
is 25 .2 per cent less ten the theoretical, due to the sc lubil i ty an d
decommosition of t is material under the drastic cooking .;onwi_tions . An
hour and a half of ad'_it_Lonal treatment improves the cellulose conten t
of the pulp by 6 .9 per cent with an increase in the yield of cellulos e
of 3 p er cent based on the wood, The latter is unexple-nable at present .
Under ordinary co_litienan increase in the cooking tame taro es a n
increase in the cellulose content of the pulp produced Baeea on wood ,
however, the actual yield of cellulose is usually less the longer th e
period of cooking .
Table 4 . --17titschoriich Lignin and Cellulose Looses in Experimental Cooks .
Cook
ITo .
?Pond
r
R47
:
Colin- :
.
: Hours
0
.
7
.
629-I
634-1
625-I
9
:
. 11-1/2
. 11
623-I
633-I
632-I
. 11-3/4 . 47 .3
: 12
. 45 .1
: 13-1/4 .
42 .7
: 15
:
Lignin : Cellu- : Lignin :
lose
lost
lost
.
Per cent
58 .4
: 28 .3
50 .2
:
20 .9
45 .9
12 .0
4 .6
4 4 .2 .
43 .7
.
3 .9
630-1
636-I
L
Cook
dura- : lose
tion
: 43 .1
.
.
.
Per cen t
. . .
7 .4
8 .2
.
12 .5
: 16 .3
14 .2
23 .'7
14 .7
. 24 .4
4 .0
3 .8
11 .1
. 13 .3
24 .3
: 24 .5
3 .0
4 .1
:
.
75 .3
. 24 . 2
15 .7
15 .3
.
Rati o
Lignin los t
Cellulos e
los t
0 .9 0
1 .3 0
1 .6 7
1 .6 6
2 .1 9
.
.
- r
:
-
4.8 4
6l
1 .70
The lignin in this series of cooks has shown a gradual decreas e
up to 12-1/2 hours of cooking . Since the best pulp 7a s produced at the
eleventh hour it is evident that factors other than lignin removal affec t
the character of p"lp . kfter twelve and one-half hours there appears t o
be a redisposition of lienin on the fiber instead of a continued removal .
Mile the lignin percentaee has increased slip:tly tee cellulose content
has diminished and the prlp is of poor quality .
'that portion of the wood which is soluble in one Der cent alkal i
p ersists almost quantitatively in the pulp through the ninth hour of cooking. -Between the ninth and eleventh hour this material is 'removed ranidl y
to abort 0 .6 of its oricinal quantity . Prom tic uil'vprlX Qtly a
very slight further decrease is noted .
In the earl* cooks the alpha-cellulose content is quite lee, .
?it'-_ longer periods of cooking, hoi-ever, the alpha-cellulose as fornd i n
00 pl-o and calc nlated. on the basis of wood shows an i .creases At th e
4u10 %ime Nip
C` =L
►~
e shows a eradval decrease to an almost nog'M
wki LI a ?'an
ellei le
very nearly constant . "he
rodi ct
s '.;crvL• .
hard. to purify and -Ea chlorin e
treatment
ably causes *
n of 11• e resinta_ t cellulose with
a corresnorine Increase in t-:.e :~41~~`" ista z' }4rtion .`~ These cooks con tainirn a small amount of 1i=-'n1
Oda. canoeqrelatl-r easil-r Dnnified by th e
chlorine-srlu p:ite method, time an igLI
cell"lose content that is fa. rl v
constant, var-ri-c bet-teen
al .7 nor cent .
is valve closely ap'L r
p roximatee the al pha-cei .lugose content of -or1Ded cotton linters, which in
o io case eras 88 .3 er ce_it, 9 Cooks lancer than eleven houre in the serie s
appear tO be of
inferior quality both c omicall T and in ap p earance . As
4 general conclusion, it se.Rae that w ith the conditions used in this series ,
*7.evea hours is the maximpm time for the production of a pulp apuroachin g
co;:
l qualiy,
an
Commercial Pulps
r
A ntmiber of commercial pulps were oietai-) .ed_ from differen t
companies and used as a standard of comparison for the :laboratory coos ..,
The analntical data for these ruins is given in Table 5 . These sample s
aka.a3 g a 64' ],lath bleat_ ed. and unbleached pulps and are sf high pnrit ;r and.
good physical p roperties . The lignin content varies from 1.3 per cen t
to 7 .8 ncr cent in the rnhleached and from 0 .5 per cent to 0 .9 per cen t
in the bleached "yelps . In none does the cellulose content fall below
90 per cent and the purest 'leached pulp rrn .s 92 .4 per cwt cellulose .
In the bleached. samp les the cellulose content is veru :high,, W ;. eft' '9,a _
per cent, and the li gnin value plus the celluloee.e totals 9'7 ..6 per cent 7 ' 1
to 99 .3 per cent . The cellulose value for unol.eached pzl.p~ is considerin
from 90 .8p er cent to9x_er cent .
911''P'ag telr„ Influencing thhF 'Pro p erties of Toed Cellulose at.
Jutted by th e
&.1omi Lion .'et :.od" b e "ark
Bra,* and.
.
Aoci'eorN
I9 Co? i,ri, n of Mood Ced1ui.o e an-3 Cotton Cellulose, J . ha* , an•' Eng . Chem . ,
W
p . 7'27 (Angu_s t 4 19 Ei .
Yet, certain unbleached pulps are of a remarkable purity being as his h
as 96 per cent cellulose and containing 1 .3 to 1 .6 per cent lignin or a
total of 96 .6 to 97 .7 per cent for lignin and cellulose . The sodirm
hydroxide-soluble content is fairly constant between the values 9 .2 t o
12 .4 per cent and in some cases slightly higher values were obtained .
Alpha-cellulose is very constant in value for all these pulps, averagin g
around 83 per cent, Beta-cellulose is within the range of 1 .4 to 4 . 1
per cent and gamma-cellulose varies very little, being between 11,6 an d
14 per cent . This gives a series of samples with varying chemica l
analyses, yet all having the pro p erties of good pulp and affording a
variety of standards each of waici meets some requirement of the pape r
industry .
Comparison of Experimental and CommercialPrl~ s
Since the eleven hour cook is the best o the experimenta l
series in its physical and chemical properties, it is ietereo} ;_n .g t o
compare it with commercial unbleached pulps made -under eunilo .r conditions . This pelp has a cellulose content of 85,8 per cent and a ligni n
content of 7 .6 p er cent .
The a l pha-cellulose content is practically id atical with tha t
of the commercial ?ripe . The some is true of the one n-->r cent sodium
hydroxide soluble and the beta- and gamma-.-cellulo yea, 7:' .e c.e 3 lulos e
content of the cocatercial pul p ., however, is con_sideraliy higher eve n
though the stable and unetable celluloses are ap p roximately the sam e
as those of the Laboratory pulps .
0
It would ap pear, therefore, that certain imn uri ties, thoug h
present in small quantities, have great influence in determining th e
physical quality of pulp . with any given pulp, even though it is withi n
definite chemical limits, length of fiber, hydration, and all other suc h
factors must be taken into account . Rather than any one factor deter mining the quality of a ;grip, it is evident that the ultirate produc t
is the result of a combination of conditions .
The single pulp, 533-I, cooked for fifteen hours with a
greater concentration of free S0 9 and lower maximum temperature, i s
even better than the eleven-hour cool : of the series . This pulp differ s
but slightly from commercial unbleached Mitocherlich spruce pulp, havin g
a cellulose content of 94,4 per cent as compared with 91 .6 per cen t
to 95 .3 per cent for the latter and 86 .8 per cent alpha-cellulose a s
against 32 .2 to 83 .6 p er cent . The lignin content of the experimenta l
pulp is 1 .8 p er cent, a value corresponding closely to that found i n
commercial pulps . Fifteen per cent bleach was consumed, indicating a
product closely resembling good quality commercial pulp .
Summarz
1. With all conditions constant except time, a series o f
spruce sulphite pulps was prepared by indirect cooking . These pulp s
were compared with commercial pulps made under similar conditions .
2. It has been found possible to compare such pulps by takin g
into consideration the cellulose content . A high cellulose conten t
appears to be necessary to produce a good pulp .
3. The percentages of stable and unstable cel1uloses are a n
indication of the quality of tae pulp, the pulp with the greater amoun t
of stable cellulose usually being of a superior quality .
4. The pulp dotoriorates with the overco>Thin g necessary t o
remove all the lignin .
5. Until the ninth hour of cooking the cellulose and ligni n
contents of the pulp are ver ;r nearly the same as those of the wood .
6. The first few hours of cooking Roes not affect the alkali-soluble material . In the latter -cart of the cook a larger amount o f
this material is rc.moved .
7. While the llaracter of the cellulose an'' to lignin content
are indicative of the quality of null) produced, other factors not wel l
understood app ear to exert considerable influence .
8. Cellulose is always lost during the removal of lignin, an d
it seems 45 per cent is about the maximum yield of cellulose by presen t
commercial methods of sulphite 'cooking .
•
Y