engineering science, but also in the arts of manufacture.
264 MICHAELIS OK LIME SULPHITE FIBER.
An engineer cannot be a school product. The ramifications of the
profession, involving every application of scientific truth and mechanical
invention to " the uses of man," have in this nineteenth century become
too numerous to be even mentioned, far less studied, in any possible
technical curriculum. There is only one practical school training for
the modern engineer; his education should be so broad, so exact, that,
when unexpectedly called upon to enter upon any given unanticipated
investigation, construction or manufacture, he can concentrate, crystal-
lize and absorb experience in a minimum space of time ; and in our very
best engineering schools, this truth controls, perhaps not avowedly, the
course of study.
My object in broaching this view is to encourage our bright young
graduates, to make them feel that even when foreign methods are in
question, as in the manufacture concerning which I write, wherein
virtually we are dependent upon cumbersome-I use the word advisedly
-talent, a very little study, a very brief experience, will enable them to
master the subject, and once mastered, "Improvements in the Manu-
facture of Sulphite Fiber " will become a famiUar caption in the Patent
Gazette.
Last fall, some acquaintances of mine, desiring to obtain information
concerning the manufacture of wood celhilose by the bisulphite process,
asked me to make an investigation. Accompanied by Mr. M. L. Griffin,
M.A., of Holyoke, Mass., an expert wood-pulp chemist, I visited Alpena
and Detroit, Mich.; Appleton and Monico, Wis.; Cornwall, Ontario;
Lawrence, Mass., and Birmingham, Conn., at which places the various
methods of making sulphite fiber were in actual operation.
Everywhere we were treated with courtesy and consideration, on oc-
casion with generous candor and unreserved openness ; indeed, it is not
likely that two seekers for knowledge in this branch of manufacture,
will ever again have such exceptional facilities extended to them.
Reports were made by Mr. Griffin and myself, and the following is in
the main the gist of what I reported; Mr. Griffin has kindly supple-
mented this by some remarks upon the chemical aspects of the subject.
As I have in view only the desire to attract the attention of those who
â– may so soon make themselves competent experts, to this opportunity
for the remunerative application of their skill. I shall not enter into
much detail, but merely give iny own impressions as simply and as
briefly as possible.
MICHAELIS ON LIME SULPHITE FIBER. 265
Sulphite fiber, or piire wood cellulose, supersedes rag stock iu paper
making. The wood, iu chips or discs, is boiled iu great digesters with
a solution of bisulj)hite of lime, and the main engineering problem lies
in the construction of a suitable, economical and lasting digester. The
processes examined, in alphabetical order, were the Graham, the Mit-
scherlich, the Partington, the Kitter-Kelluer, and the Schenk.
The investigator is at once struck by the astonishing diti'ereuce in
size and boiling pressure between the Mitscherlich and all the other di-
gesters ; the former is 14 x 40 feet, the largest of the latter 10 x 28 feet;
the steam gauge on the former registers 40 to 45 pounds, while on all
the others, 75 to 80 pounds. Why these differences? The reply to both
these suggested questions develops an intrinsic difference of operation
between the Mitscherlich and all the other systems. The boiling point
of liquids rises with the pressure, and Avhile in all these sulphite pro-
cesses Ave have to do with a solution of greater specific gravity than
water, for purposes of comparison we can consider the temperature of
the boiling point of water. According to Raukine, under a pressure of
40 to 45 pounds water boils at 267 to 275 degrees Fahr. ; at 75 to 80
pounds, at 308 to 312 degrees. Hence Mitscherlich boils at about 40
degrees Fahr. lower temperature than the others, consuming, of course,
more time for comjjlete conversion, and to compensate, he boils a greater
quantity.
Professor Mitscherlich claims that the slower boiling yields a better
and surer output. His digester turns out from ten to fourteen tons, the
others from one and a half to three tons, at a " boil." He requires for
cooking from forty-five to seventy-two hours; the others, from fifteen to
twenty-four.
Exteriorly all the digesters are of metal, all of open-hearth steel or iron
plate, excei^t the Schenk, which is of so-called deoxidized bronze. All
are approximately cylindrical, except the Partington, which is spherical.
The cylinders are uiDright in the Ritter-Kellner and Schenk processes ;
in the Mitscherlich and Graham they are horizontal. The digesters
are fixed, with the exception of the Partington and Graham, which
revolve, the Graham about its longer axis.
Upon carefiil exterior survey of the digesters, I was struck by the
fact that both the Partington and Ritter-Kellner were tapped at numer-
ous points, and the holes closed by screw plugs. I learned that the
jiuriDOse of these vents was to locate leaks ; indeed, at Monico theso
266 MICHAELIS OX LIME SL'LPHITE FIBEK.
holes were not closed, and the sulphite solution exuded in perceptible
quantity.
Considered merely as a vessel strong enough to stand a given pres-
sure, the only available substance of which the digester can be made,
looking from an economical standpoint, is iron or steel. The majority
of the digesters are made of rolled iron plates ; the Detroit, of open-
hearth steel. There is no reason why our gun iron, with a tensile
.strength api^roximating 40 000 i^ounds, should not be available for
digesters. They could be turned out in sections ready for assembling ;
the advantages of such a substitution for the complicated rivet-work
shell are evident. At remote inland i^oints the large digesters must be
assembled hi situ, and boilermakers must now be transported for the
purpose, A properly handled wrench would suffice to set up the sec-
tional cast-iron construction.
A 14 X 40 feet cast-iron digester has been designed, with a factor of
safety of 6, which will cost less than the riveted apparatus, to say
nothing of the facility with which it can be transported, and the ease
with which it can be assembled by unskilled labor.
We come now to the inside of the digester. Owing to the well
known affinity of the bisulphite solution for iron, all digesters made
of this metal must be lined with a resistant, fluid-tight material, as a
jn-otection against the solvent action of the "acid" mixture. The
Schenk digester, a uni-metal construction of deoxidized bronze, is
assumed to be sutficieutly resistant to the solution without protecting
lining. Tha Graham, Partington and Ritter-Kellner digesters are all
lead-lined, the Mitscherlich, fire-brick lined. I use the word "fire-
brick " for want of a better. The bricks used are of special form, and
are made of a German refractory clay, which seems to me to be about
the same as is used in the manufacture of the Nassau Seltzer jugs.
DiGESTEE Linings.
The vital point in thesj sulphite processes lies in the ability of the
digester to resist the erosive action of the acid solution and its gaseous
products. Lead has for centuries been used as a lining material in the
manufacture of sulphuric acid, so that its application to the present
sulphite fiber processes lay near at hand. It is used in the Graham,
Partington and Ivitter-Kelluer digesters.
MICHAELIS ON LIME SULPHITE FIBER. 267
Lead Lining.
In speaking of the sul plate process, the Encyclopedia Britaunica uses
the following language :
" The pulp or fiber produced by all these processes is of excellent
quality, and can be prepared at a cost greatly lower than the soda pro-
cess. The strength of the fiber is maintained unimpaired even after
bleaching, and white paj^er made solely from such fiber is in every
respect superior to that manufactured solely from pulp prepared by
boiling with caustic soda.
' ' Dr. Mitsclierlich's process has been extensively adopted in Germany,
and there seems little doubt that these processes will in time supplant
the use of soda in the case of wood. The great objection to them all is
that, as they all depend on the use of bisulphite, which, being an acid
salt, cannot be worked in an iron boiler, the boiler must be lined with
lead, and great difficulty has been encountered in keeping the lead lin-
ing of the boiler in repair."
The i^rimary, indispensable condition in protecting iron sulphite
boilers with lead, is that the lining must be continuous — that is,
liquid-tight.
Now, lead has a linear co-eflicient of expansion much more than
double that of iron ; in these processes it is subject to a change of tem-
perature of at least 240 degrees Fahr. (300-60 degrees), and the una-
voidable resulting flow of the metal cannot be comjjensated for by
permitting sections to expand and to contract freely upon each other,
for that would require open joints, a violation of our primary condition.
The lead lining must in some way be attached to the iron shell, for
otherwise it would soon collapse, or go to pieces in some other way.
Only three practical ways offer themselves for the attachment of the
lead lining to the iron.
It may be bolted on at proper points ; it may be, to borrow a plum-
ber's phrase, "tacked on," at appropriate places, or it may be com-
j)letely soldered on. The first two methods permit, as is evident,
under variations of temperature, changes in the superficial area of the
lining ; the latter method forcibly resists this, and limits the flow of
the lead during the life of the solder union to molecular expression
only.
268 MICHAELIS ON LIME SULPHITE FIBER.
Paktington.
This boiler, it will be remembered, is spherical ; the lead is applied
in spherical lunes, clamjjed to the iron, and burned to each other. The
theory is that it is an easy matter to replace an injured section, and
thus to keep the lining intact at comparatively little cost. At Monico,
the vents in the shell, already spoken of as "leak locators," were all
open, and, — the descriptive aptness of the words would be appreciated
by any eye witness, — in eruption. Having had some experience in lead
burning, I noticed at Monico extensive preparations for conducting it,
and, in answer to my inquiries on the subject, the genial and capable
superintendent admitted that he had had great trouble with the lining.
Indeed, the visible debris and the evident condition of the boilers
were cogent evidence. It is needless to make further comment ; " he
who runs, may read " is here ajsplicable. I learn that since my visit
these boilers have been destroyed by fire, and have been replaced by
another construction. At Lawrence, where a battery of eight Partiug-
tons is in ojjeration, the digesters were certainly more presentable; but
there I observed that the usual hand apparatus for lead burning w^as
apparently not considered sufficient, for the manager had applied an
installation furnished with a power pumj), and a system of conducting
air and hydrogen pipes in situ at each boiler.
It is evident that in the Partington digester, the lunes must bulge
from the iron under expansion, and must again be forced into con-
tiguity under contraction and pressure. Hence, there is periodic
" flapping," which, it seems to me, must in time result in Assuring. Of
course, constant watchfulness and timely burning would prevent
destructive results upon the shell. The expense of this can only be
inferred from the statements made in regard to the cost of the output.
Neither at Monico, nor at Lawrence, was an opportunity offered to make
an interior examination. At Monico, such examination would have
been merely a work of supererogation.
The Eittee-Kellner.
The digester, about 10 x 28 feet, is built up of cylindrical sections,
4 feet wide, a few inches apart, and fastened by heavy exterior bands.
The object of this construction is to provide the means for attaching the
lead lining peciiliar to this process.
MICHAELIS ON LIME SULPHITE FIBER.
2G9
The spa:!es between these sections form annular dovetail mortises
thus:
A. — Boiler Shell.
B. — Exterior Band.
C. — Annnlctr Tenon of Lead and Antimony Alloy.
These mortises are filled with an alloy of lead and antimony, and at
the ends of a diameter meet similar vertical tenons, to which they are
attached. The lining is burned fast to this semi-cylindrical frame.
Here, again, under the irresistible force of expansion, these great sheets
of lead, roughly sio3aking 16x4 feet, miist theoretically, if the tacking
holds, "ijuckerup," and again be forced back against the shell under
contraction and pressure.
Again, it seems to me that this constant movement to and fro must,
in the end, bring about Assuring. At Cornwall we were told no trouble
of this kind has been experienced, and the digester we entered, more
than half filled with chijis, showed no evidence of degradation detect-
able in the very brief time at our disposal.
I asked two bright prominent officials, one of the parent, the other
of the Canadian company, " What becomes of the increased superficial
area due to the difference in the expansion of the iron and lead ?" One
said he didn't know and had no theory on the subject, the other replied:
" This is no longer a matter of theory, it is an accomplished success."
The digester is, however, provided with abundant vents, or leak
locators, and in reply to my question regarding their practical value,
the gentleman in charge explained to me that by using a pneumatic
pump the noisy issue of the air through the nearest vent located the
leak. This was so graphically told, that I was at once convinced the
descrii^tion was founded upon auricular observation.
270 MICHAELIS ON LIME SULPHITE FIBER.
The Geaham.
The Graham digester, 7J x 22 feet, is made of sheets of boiler plate,
to which the lead lining is soldered before bending and assembling.
The method of doing this is ingenious and simple.
The sheet is cleansed, and smoothed by a radially traveling emery
wheel; it is then firmly fixed for half its surface over a gas-jet heater.
The rectangular frame that holds it down is packed with fire-proof
packing where it rests upon the i^late, thus actually forming a water-
tight vessel, of which the iron to be leaded is the bottom. The plate is
copiously doused with a solution of chloride of zinc, and when heated
to the proper tlegree molten lead in sufficient quantity is poured upon it.
Although the promoters of this process do not so call it, it is, never-
theless, soldering, which is authoritatively defined to be "the jirocess
of uniting tw^o pieces of the same or of diff"erent metals by the interposi-
tion of a metal or alloy, which, by fusion, combines with each."
Here the metals to be united are lead and iron; the " metal or alloy "
is zinc, or zinc and lead. I emphasize this simple matter because it is
claimed that in the Graham process the two metals are united by a
special alloy of lead and iron.
I quote from the company's courteous, well posted expert:
" Our boiler obviates these defects and overcomes the difficulties and
repairs and constant iusiDection to which ordinary lead lined boilers are
liable. This is because the lead is united to the iron or steel uniformly
by means of an alloy at the point of junction between the steel and
lead, and the crystals of the two metals are intimately mixed at the
point, so much so that it is impossible with a cold chisel to cut the lead
away from the irou or steel without still leaving a thin surface of lead.
The junction alloy of steel and lead has also a greater breaking strain
than lead itself, it having been subjected to breaking tests."
A standard authority states that "an alloy is a combination by fusion
of two or more metals, as brass and zinc, tin and lead, silver and copper,
etc." Hence to speak of "the junction alloy of steel and lead" is in-
correct, for in the coating operation there is not even an approximation
to the melting i:)oint of iron.
The alloy of lead and iron appears to be almost unknown in the arts;
and that this so-called " junction alloy of steel and lead," or, as I think,
of zinc and lead, should possess a greater tensile strength than the lead.
MICHAELIS OX *LlME SULPIJITE FIBER. 271
is not strange, it is not an unusual iiroperty of alloys; thus one con-
sisting of 12 parts lead and 1 part zinc lias six times the tenacity of lead.
I must also put on record iny lack of faith in the natural inference
that would be drawn from the claim that the two metals (iron and lead)
are intimately mixed at this i^oint (the junction or cementation surface),
" so much so that it is impossible with a cold chisel to cut away from
the iron or steel without still leaving a thin surface of lead." Under
favorable circumstances the lead can be "peeled" from the iron — I
have done it myself.
I examined the Graham process after the Ritter-Kellner at Cornwall,
and it struck me at once as a logical consequence that if " tacking " the
lead on in places only gave satisfactory results, then complete cementa-
tion ought to do even better. Upon reflecting, however, I modified this
hasty conclusion — for the governing conditions in the two processes are
entirely different. In the Ritter-Kellner the lead is burned to the
circular and vertical tenons.
Burning is defined as "joining metals by melting their adjacent
edges, or heating the adjacent edges and running into the interme-
diate space some molten metal of the same kind." A well known writer
says :
"The articles burned together being homogeneous, the parts expand
and contract evenly by changes in temperature ; the solders have a
greater range of expansion by given changes of temperature than the
metals they connect.
" The solders oxidize oioi'e or less frealy than the metals they connect,
and establish galvanic circuits which destroy the integrity of the joint,
especially in the presence of heat, moisture or acids."
One would almost suppose the aiithor had sulphite digesters in
mind.
In the Ritter-Kellner there is little danger of the joints loosening.
In the Graham, under periodic expansion and contraction and galvanic
action, I should fear a sundering between the lead and iron; if this did
take place the boiler would very soon become unserviceable. Even
granting the claim that the lining and sheet are indissolubly connected
by an alloy of lead and steel, and that the "lead, being the weaker metal,
when fastened homogeneously to the iron or steel, has to obey the ex-
pansion and contraction of the iron or steel," there still remains an ap-
l^arently insuperable difficulty. The lead lining is at least half an inch
272 MICHAELIS ON LIME SULPHITE FIBER.
thick, and even supposing that the cylindrical laminfo in homogeneous
contact with the iron are docile, and move in military cadence with
their inseparable stronger companion, yet the balance of the lead must
be subjected to a recurring ebb and flow for which no comi^ensation is
l^rovided. I quote from the Graham expert:
' ' The explanation of the iron controlling the lead expansion is easy to
understand. Lead is a very malleable metal, its crystals fitting loosely
together, i. e., there is comparatively a large space between the crystals
as against other metals, and if the ci'ystals of lead were counted over 22
feet (the length of the digester), and the number divided into one-third
of an inch (the linear expansion of lead for 90 degrees in 22 feet), it
would be found that the fractional part of this one-third inch would be
considerably less than the spac3 between each crystal, and there is no
chance of one crystal pushing another one, as in metals where crystals
are closer together."
On this theory I do not understand why lead should expand measur-
ably under ordinary increase of temperature. Further, the common
experience of every plumber militates against the correctness of the
assumption.
Lead pipes for hot water will "creep" under fluctuation of temper-
ature without perceptible increase of length; this is very evident when
the pipe under a metallic clamp is examined ; a l^urnished band is seen
protruding beyond the clamp. I have seen this in less than twenty-four
hours after brand-new pipes were installed.
It is a well known fact that in hotels, for instance, where a large
quantity of hot water is used in the morning and very little during the
rest of the day, the pipes being thus subjected to frequent and compara-
tively great changes of temperature, this very movement of which I have
spoken, to use plumbers' parlance, " kills " them. That is, they lose
all elasticity, become brittle and crack, showing a crystalline fracture.
Now, I am inclined to think that there is danger of such a result with
the lead lining of the Graham boiler, even if the cementation remain
intact. The lead, under this constant, enormous molecular stress, will
degrade, become brittle, porous, crack, even drop off. (See Note 1.)
Then the boiler is ruined, for the lining, under such circumstances,
can neither be repaired nor replaced.
Although I have not seen the patents issued to the Graham Com-
pany, yet I am of oi)iuion that they can afford but slight protection.
MICHAELIS OX LIME SULPHITE FIBER. 273
The lead coating of iron has long been well knowu in the arts, as seen
in terne plates, and no modern patent can limit the amount of lead that
may be applied.
Brick Lining. — The Mitscherlich.
The Mitscherlich digester, as already stated, is lined with an acid-
proof brick of special design, laid in Portland cement.
Apparently a startling innovation, reflection proves that this method
follows out the direct line of modern progress. The manufacture of
that almost indispensable article, sulphuric acid, has in comparatively
late years be3n greatly improved and facilitated by the introduction of
the Gay-Lussac and Glover towers, edifices lined, not with lead, but
with acid-proof tiles or brick. It is a curious coincidence, in this con-
nection, that about seven years ago one of the leading American sul-
jjhuric acid makers told me that he had found that Seltzer jugs made
the most resistant tower linings. The transition from brick-lined
towers to brick-lined digesters must have been no difficult task for so
able a scientist as Dr. Mitscherlich.
The ability of fire-clay to withstand enormous stresses is familiar to
us all. The Bessemer Converter and the Open -hearth furnace are illus-
trations in point.
The co-effi:-ieut of expansion of fire-brick is only about 40 per cent,
that of iron; in a length of 40 feet for a change of 180 degrees Fahr. a
fire-brick construction would expand linearly less than one-quarter of an
inch. Mortised and tenoned together, due to the special form of brick
used, and laid in Portland cement, it constitutes a homogeneous mass,
whose integrity is not jeoparded by usual fluctuations of temperature.
I have examined, with the utmost care, digesters that have been in
use for nearly two years, and have failed to discover any intrinsic defect
in the lining. The best steam boiler imaginable is liable to blow up if
not handled with ordinary care, and so doubtless must an average de-
gree of watchfulness be exercised in the use of the Mitscherlich, as well
as of any other digester. An absolutely automatic digester, that fills,
cooks, empties and cleans itself, is still an undiscovered desideratum.
The cement joints are now and then superficially j^ercolated by the acid
solution; they give clear warning of this percolation by discoloration; a
cold chisel to cut out the affected mortar, and a trowel to repoint with
cement, afl'ord a ready, inexpensive, efficacious remedy.
274 MICHAELIS ON LIME SULPHITE FIBER.
In one of tlie digesters I noticed a patch back of one of tlie ui^per
min-holes. The cause of the corrosion was very apparent, and its oc-
currence inculcated a valuable lesson. The man-hole is lined with lead,
this is "bent under," flanging well back of the intersection of the man-
hole cylinder with the digester. The brick lining comes up to this well,
and, of course, has an open circular junction line, which must be kept
well pointed, as at present constructed. This was neglected, the liquid
penetrated, followed the lead, and ate its way through the iron. Such
an accident can only occur under long continued, persistent neglect.
I know of no engineering objection to a brick or tile lining for a low
pressure digester. Such constructions, as already stated, do withstand