Year: 1886

page_text: I, OLIVER IMRAY of No. 28 Southampton Buildings, Chancery Lane, in the
County of Middlesex, Fellow of the Institute of Patent Agents, do hereby declare
the nature of this invention and in what manner the same is to be performed to
be particularly described and ascertained in and by the following statement :-
This invention relates to a process and apparatus for restoring the spent acids in
the manufacture of pyroxyline compounds.
The accompanying drawing illustrates apparatus employed.
Fig. 1 is a side elevation.
Fig. 2 a plan of the acid drum, and Fig. 3 a section of the rubber plug and
connecting pipes for it.
In manufacturing soluble pyroxyline, it is usual to prepare a standard mixture
of nitric and sulphuric acids, in which is immersed some form of cellulose, such as
paper, cotton or other fibre. After immersion for about half an hour, the cellulose
thus converted into nitro-cellulose, is removed from the acid bath, and the adhering
'spent acid," amounting to nearly one fourth of the original bath, being partly
removed by means of a centrifugal machine, the nitro-cellulose is washed with
water until all traces of acid are removed.
"
The acid bath is then replenished from the standard mixture, and immersion of
cellulose repeated. The spent acid removed by the centrifugal machine is usually
treated as a bye product, to be returned to the chemical works, and there credited
at about one fourth of its original cost, exclusive of labour, handling, re-packing,
shipping, transportation, breakage of carboys &c.
It would seem that the acid separated from the nitro-cellulose by the centrifugal
machine is supposed to differ from that left in the converting vessels, and the fact
that they are identical, if it is not overlooked, is at least disregarded; meanwhile
this spent acid accumulates in quantities, fifteen to twenty times the weight of
nitro-cellulose produced. But the most serious defect of this mode of nitration lies
[Price Sal

page_text: in the step by step weakening of the converting bath at each successive immersion,
so that the product of the first immersion differs in quality from each subsequent
immersion, the per centage increase of weight diminishing in proportion, and giving
rise to the observation that "no two batches of pyroxyline are alike." Owing to
this unsatisfactory state of the process, from time to time the acid is emptied from
the converting pots and returned to the chemical works as "spent acid."
Some manufacturers have erected settling tanks, devised processes of filtration
or precipitation and having accumulated a large quantity, have subjected it to
analysis and corrected its defects.
The object of the present invention is to secure uniform quality of product,
greater yield, means of using spent acid over and over again until consumed, while
avoiding the labour, cost and time in clarification, filtration, settling, etc; so that
one fourth the stock of acids usually required suffices to supply a factory.
The plant required for this process consists mainly of:
1. A turn-table mounted with eight converting vessels, each preferably having a
capacity of about thirty gallons.
2. A centrifugal machine.
3. A "spent acid" tank.
4. A "concentrated mixed acids" tank.
5. A "building up acid" tank, with appliances.
6. A temperature controlling coil.
7. A dumping trough, with water supply, drainage, etc.
8. A washing tank with pure water, supply, drainage, etc.
There should be a supply of air at a pressure of about twenty pounds to the
square inch, and guages and other necessary appliances. Each of the eight con-
10 T71
Cuntalabond mind" aid fan
A convenient charge of cellulose (fine tissue paper, bleached cotton yarn, bleached
ramee, or the like) is, one kilo and three hundred and twenty five grammes, to the
150 kilos of acid, and the time of immersion should be about 241 minutes. The
temperature of the acid, 85° F, is adjusted by passing it through a tempering coil,
without having recourse to the old method of immersing a copper coil heated by
steam or cooled by water which interferes with nitration, and involves the risk of
steam or water escaping into the acid. The composition of the "concentrated
mixed acids" for manufacturing soluble pyroxyline is:
Sulphuric acid H. SO, from 58 20 to 65.00 per cent.
20
100 00 του ου
The acids are weighed in the iron drums and forced direct from the drums by
compressed air into the concentrated mixed acids tank. The "Building up Acid,'
serving to refill the converting vessel after each immersion, consists of concentrated
mixed acids, about one part, by volume-256 lbs. by weight. Spent acid from
centrifugal machine about five parts, by volume-1260 pounds by weight.
The "Building up acid tank" should be of large capacity so as to contain two
days' supply if necessary, or better, there should be two of these tanks, so that a
day's supply may always be ready a day beforehand, without requiring night
labour or work. The cellulose is introduced into the successive vessels of acid at

page_text: "
intervals of three and one-half minutes, so that by the time the first charged vessel
arrives at the centrifugal machine, the eighth vessel has received its charge. Thus
the time of action in each vessel is 24 minutes which is sufficient for conversion
of thin tissue paper. The nitro-cellulose is now rapidly transferred from the con-
verting vessel to the centrifugal machine which in two or three minutes separates
about 32 Kilos of spent acid, which flows by gravity to the spent acid tank. The
rinsed nitro-cellulose which persistently retains from six to seven Kilos of acid is
next plunged beneath water in the dumping tank, whence it passes into the
washing tank. On an average each converting vessel loses 38.4 Kilos in weight,
the contents having deteriorated in strength. By the old method, this deficiency
was made up by "normal standard mixed acid "leaving one hundred and twelve
kilos of spent acid in each converting vessel unfortified, and as this omission was
repeated twenty-five times a day it could be readily understood that, no two
batches of pyroxyline were alike," for each day's product was made up of various
qualities. By the present invention, instead of using the "normal standard
mixed acid" to replenish the converting vessels, and rejecting more or less of the
spent acid from the centrifugal machine, there is employed what may be termed
building up acid," which includes all the spent acid of the previous day's working
fortified with "concentrated mixed acid" this being applied under the following
conditions. 1. All the spent acid separated by the centrifugal machine the one
day, is reserved for the next day's work. 2. The volume of concentrated nitric and
sulphuric acids added, does not exceed the volume of spent acid lost in the washing
water. 3. The concentrated nitric and sulphuric acids contain not only the same
equivalents as a like volume of "normal standard mixed acid," but also in addition
enough nitric acid to replace that consumed in nitrating 1325 grammes of cellulose,
and lost in fumes during conversion, and in the centrifugal machine. 4. The
degree of concentration of the new acids used with the spent acid is such, as to
take up the water formed both by the chemical reaction, and by absorption from
the atmosphere, during the time of conversion. 5. The building up acid, is not
so concentrated, nor so different from the normal standard mixed acid, that if
accidentally there is an over supply or an under supply in a converting vessel,
the product is seriously affected. By observing these conditions, soluble pyroxy-
line is produced on the large scale of uniform quality, and without perceptible
deterioration of the acid-bath. By the use of eight converting vessels, one
centrifugal machine and one dumping trough of water, since a converter is
charged every three and a half minutes, seven intervals each of three and a half
minutes occur between immersion and removal, or a period of about 24 minutes
is allowed for converting the cellulose into nitro-cellulose. Also at every inter-
mission of three and a half minutes, there occur an immersion of 1325 grammes of
cellulose; a removal of nitro-cellulose to the centrifugal machine and thence to the
water tank, a flow of about 32 Kilos of spent acid to the spent acid tank, and a
replenishing of a converter with 38.4 Kilos of building up acid, ready for the next
cycle of immersion etc.
After nitration, about three-fourths of the acid remain in the nitrating vessel;
about five-sixths of the abstracted fourth is separated by the centrifugal machine
from the dripping nitro-cellulose, and passes into the spent acid tank, whilst the
remaining one-sixth of said one-fourth persistently adhering to the nitro cellulose
during centrifugal action, is lost in the washing water. For restoring the acid, the
contents of the spent acid tank are forced up into the "building up acid tank,"
the increase therein, as shewn by inches of the glass gauge being noted for instance,
forty inches; from the concentrated acid mixture enough is now directed, to raise
the level of the acid in the "building up acid tank" from seven to eight inches
bigber; as soon as a charge of "acid dripping nitro-cellulose" has been transferred
from a nitrating vessel to the centrifugal machine, the turn-table is moved so as to
bring the converting vessel from which the nitro-cellulose has been removed,
beneath the stop-cock of the "building up acids tanks," and, a volume of this

page_text: "building up acid " equal to that removed with the nitro-cellulose, is permitted to
flow into the converting vessel until the normal level indicating a charge of
150 Kilos is reached. Thus about one twenty-fourth of concentrated mixed acid
by volume, or 64 kilos by weight, together with a volume of spent acid equal to
that removed by the centrifugal machine from one batch of nitro-cellulose, being
about 32 kilos practically restores the 1116 Kilos of spent acid, left in the con-
verting vessel to its norinal strength and volume of 150 Kilos, ready to nitrate
another batch of 1325 grammes of cellulose. The weights or volumes above
mentioned also the proportion of tissue paper or other form of cellulose to the acid
may be somewhat varied. The quantity of nitric acid should be slightly increased
when the atmosphere is saturated with moisture in summer, and diminished slightly
in winter.
The product itself serves as a guide to a skilled operator shewing that more
building up acid is required when the converted cellulose appears ragged, soft or
burnt through, technically termed as "being cut" and that less building up acid is
required when it is found on washing and drying, to be imperfectly dissolved in a
solution consisting of one part of camphor to ten parts of alcohol. Usually it is
deemed necessary to use stoneware converting vessels, but according to the present
invention, cast iron vessels steeled or rendered malleable by exposure to continued
heating, surrounded by infusorial earth, or iron peroxide are used, the action of
acids upon the metal forming a ferric sulphate, which being insoluble in the acid
mixture, does not injuriously affect the product. Also, according to this invention,
Bessemer steel, homogeneous metal or mild steel are used for the tanks, this metal
practically resisting the action of the acids, there being only a slight formation of
ferric sulphate, that precipitates very slowly, (owing to its specific gravity being
nearly that of the mixed acids), whilst gaseous nitrous acid seems to interpose
between metal and acid preventing further action. Owing to this, the operation
of coating wrought iron vessels with paraffine or acid resisting compounds, as
practised heretofore, is dispensed with. Also by using iron tubing and iron stop-
cocks the plant is of metal throughout, thus avoiding the great expense of stone-
ware, also the weekly coating with paraffine, materially improving the apparatus,
and greatly simplifying and cheapening the manufacture on a large scale. Instead
of using for the tanks, covers, made removeable to admit workmen to paraffine the
interior, a mere manhole suffices; and ordinary sheet iron drums such as are used
for transport of glycerine suitably strengthened are employed for storing nitric or
sulphuric acid.
Such a drum, after being weighed, has inserted in it a plug, which carries an air
tube and a tube reaching to the bottom, then on admitting compressed air the
contents are raised to the required level. After the drum is emptied, the tare gives
the weight of acid taken. In providing for the addition of a certain proportion of
concentrated mixed acids to a certain proportion of spent acid, there are required
only three tanks whose total contents need be much less than those of which 30 are
usually employed involving a large quantity of dead stock.
Every unnecessary vessel is a disadvantage because extended surface tends to
weaken the acid by absorption of moisture, and the acids become deteriorated
according to time and extent of metallic surface exposed. It may be here noted
that in nitrating paper &c., the so called "flock" instead of being as flocculent
matter detached from the fibre, is simply ferric sulphate Fe, (SO), which being of
nearly the same specific gravity as the normal acid mixture is slow to settle. Being
insoluble in the concentrated acids it is innocuous during nitration and as it is
completely soluble when diluted with water, it disappears in the washing of the
pyroxyline.
Referring now to the accompanying drawings A. is the spent acid tank, B. the
building up acids tank, C. the temperature controlling coil, D the concentrated
acids tank, E a drum for acid, N. weighing machine. A¹ waste pipe from centri-
fugal machine to spent acid tank A. B¹ delivery pipe from spent acid tank A to

page_text: building up acid tank B, C¹ delivery pipe from concentrated acid tank D, to building
up acid tank B, D₁ delivery pipe from drum E to concentrated acid tank D,
Epipe for admitting compressed air into drum E, F¹ and G glass gauges for con-
centrated acids tanks and building up acids tank. H. H¹ emptying cocks for
tanks D and B respectively. K. L. M, man-holes to tanks A, B and D. O con-
necting pipe from building up acid tank B to coil C. P delivery pipe and
controlling stopway for conveying built up acid of suitable temperature to replenish
nitrating vessels. The compressed air pipes Q, R and S should be inserted in or
near to the sides of the manhole of tanks A, B and D; air pipes T and U with
stop cocks passing down the tanks B and D, to about six inches from their bottoms
serve for agitating and thoroughly mixing the acids in these tanks. Z is a pressure
gauge. VW and X are pipes leading air and nitrous gas through the main Y to
the ventilator.
"
The apparatus is worked in the following manner. Assuming that the spent
acid tank A contains the accumulation of a day's working received through pipe A¹
from the centrifugal machine m. First, on gauge G, the level of acid in the
building up acid tank B is marked then on closing stop-cocks o and q and opening h
and the compressed air causes the spent acid to rise up the pipe B' into the
building up acid" tank B, raising the level as shewn by the gauge G, say sixty
inches. On then closing stop-cocks i h and q and opening and having marked on
gauge F¹ the level, the stop-cock u is opened and acid passes from D by pipe C¹
to B. When the gauge G indicates 12 inches rise beyond the 60 inches before
noted, the stop cocks u and j are closed, and the compressed air supply cock T is
opened to produce agitation, the air escaping by the opened cock. It is better
to defer the agitation until the mixture has cooled down to about 70° F. To prepare
the concentrated mixed acids for tank D, a drum E of nitric acid of suitable strength
is rolled on to the weighing machine, and its gross weight is noted. Around the
drum is placed the rectangular frame a¹, and its blocks a a are screwed up against
the ends of the drum heads by the setting screws b. The plug F with its pipes is
inserted in the hole of the drum, and the pipes are connected. The cocks of D
and E¹ being then opened the pressure of the air forces acid from E into D, and by
comparing the elevation of level in D as indicated by the gauge F1, with the loss
of weight of E it can be ascertained how many inches of level are equivalent to a
given weight of each acid as a guide in future working.
The contents of several drums of nitric acid of proper strength having been
transferred to D, the required proportion of sulphuric acid of suitable strength as
described for "Concentrated inixed acids) is computed and a proper number of
druins of sulphuric acid are transferred to D, care being taken to compare weights
with rise of level in D as already described. In adding the sulphuric acid, sufficient
time should be allowed after each drum added, for the mixed acid to cool, as over-
heating might damage the tanks. By the method of transfer described, one weighing
suffices to check invoices from the chemical factory, and to guide subsequent supplies
of the acids by volumetric measurement indicated by the glass gauges, and as all
transfers take place in closed vessels, except in charging the converting vessels,
waste and fumes are avoided.
By the process carried on as described may be manufactured any of the three
varieties of pyroxyline known as (1) gun cotton (2) collodion or soluble pyroxyline,
and (3) xyloidine each of these, or mixtures of them being produced by increased
or diminished strength of acids, the proportions of which may be varied.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is:-
1. In the manufacture of pyroxylines, the process herein before described, of
restoring the spent acid of a nitrating bath, by means of a mixture of spent acid

page_text: from drained pyroxyline, with concentrated nitric and concentrated sulphuric acids,
in about the proportions and substantially in the manner described.
2. The combination of a spent acid tank, a building up acid tank, a concentrating
acids tank, with a temperature regulating coil.
3. In combination with a drum E, a strengthening frame a¹ with pressing
blocks a and setting screws b and a plug and pipes F, arranged for forcing acid
from the drum by pressure of compressed air substantially as described.
ABEL & IMRAY,
Agents for the Applicant,
28, Southampton Buildings, London, W.C.