INVENTION IN ITS APPLICATION TO WASTE RECOVERY
The necessity to conserve our industrial resources, which is so
pronounced to-day, is acting as a powerful stimulant to inventive
effort. The mere circumstance that approved apparatus exist for the
reclamation of wastes and are readily available to those of a thrifty
or enterprising turn of mind no longer suffices to meet the situation.
In the past we have been content to practise waste recovery along what
may be described as satisfactory lines, but satisfactory only in so far
as they represented an attempt to turn refuse to commercial account. In
many instances the appliances employed have only been extemporized and,
as may be imagined, are far from being efficient. They only enable a
certain proportion of the available materials to be recovered. In many
instances residues treated for fats have carried away just as much of
the essential article after treatment as were actually recovered. In
other words, the work was only half completed: the system followed has
been unable to give a higher yield owing to errors in its design and
construction.
Waste recovery as it should be practised to-day is a science. It is
just as precise a science as the extraction of nitrogen from the
atmosphere, the smelting of steel, or the production of artificial
silk. Hit-and-miss methods may have sufficed during the years when
commodities were cheap and plentiful, but to-day there is a world-wide
stringency in the supply of anything and everything necessary to
commerce. As a consequence prices are ruling high, and so the practice
of waste recovery along extremely well-defined scientific lines is
essential.
The harnessing of science to this peculiar industry is imperative for
more reasons than one. As the process of extraction, say of fats,
is pushed to its logical conclusion, the task becomes more and more
exacting and expensive, demanding the employment of refined methods.
It is far more difficult to draw from the material the last ounce
of possibly reclaimable fat than to whip out the first ounce. The
last-named is surrendered readily, but to recover the first-named
enormous persuasive effort is entailed.
But it is the uttermost ounce which the scientist is determined to
obtain. Easy conquest does not appeal to his well-ordered mind, and
so we see a spirited struggle in progress to increase efficiency. At
the same time in attaining this eminent factor the inventor must keep
his eye and hand upon the issue of cost. If it is going to cost more
to extract the last absolute ounce than that ounce is worth, then the
effort is futile. Commercialism, which considers inventive ingenuity
merely from the angle of pounds, shillings and pence, or dollars and
cents as the case may be, is not impressed by the mere beauty of any
process or apparatus.
The financial issue is surveyed from every possible angle--capital
outlay, fuel consumption, simplicity of operation, maintenance charges,
depreciation, renewals, and labour. Any one of these several factors
may be sufficient to cause the refusal of an advocated process, while
should they be experienced cumulatively then the likelihood of the
process being adopted is extremely remote. Waste recovery is such a
sensitive range of endeavour as to prevent all consideration along
philanthropic lines.
An instance in point may be narrated to indicate how perplexing and
intricate the problem is. As is well-known, wood, in common with
all vegetation, carries a certain proportion of alcohol, a product
in keen demand for numerous industries. It is also common knowledge
that in working wood enormous waste is incurred, notably in the
form of sawdust. This fact induced inventors to attack the problem
of extracting the alcoholic content from this residue. Laboratory
experiment confirmed the practicability of the project, and even went
so far as to indicate how the idea might be commercially developed.
But there is a tremendous gulf between the laboratory and the factory.
It was many years ago that the possibility of extracting alcohol from
wood first aroused the serious attention of the industrial chemists.
They are still wrestling with the problem. Time after time the world is
startled by the announcement of a new and inexpensive process for the
distillation of alcohol from wood and the prospect of extracting whisky
and other popular beverages from sawdust excites intense interest.
But, metaphorically speaking, nine days later a strange silence is
encountered. The new process has vanished from aught but a memory of
much claimed but nothing forthcoming. Fortunes have been sunk and lost
in the attempts to solve this momentous problem, and it is probable,
from the state of knowledge and the stage of experiment at the moment
attained, that many millions more will be expended before commercial
success is achieved. One of the greatest obstacles to the realization
of the chemist’s dream has been the extremely high temperatures to
which resort has to be made, which plays sad havoc with the plant
involved, and the charges incident to the renewal of which are so heavy
as to render the financial outlook extremely depressing. Even the
conditions of war, which scouted all considerations of expense, have
not carried us an inch forward. We built one factory to conduct the
distillation of wood for the alcohol which was so sorely needed, and
planned a second installation. The first factory was promptly abandoned
after the signing of the armistice, while the second factory was never
completed, owing to the indifferent results achieved with the conduct
of the initial plant.
Similar experiences may be narrated in many other fields of attempted
waste recovery. Fortunately, however, for every dismal failure recorded
a dozen or more overwhelming triumphs can be related. It is this
circumstance which induces the experimenter to persevere upon his
ventures of discovery. But this is not the only satisfactory feature
of success in this field. The spirit of rivalry is so keen that the
industrial chemist and the chemical engineer are for ever striving
might and main to improve the methods which they have evolved, and
in the determination to secure the uttermost ounce of the elusive
fat, they proceed to extreme lengths. The eternal quest for improved
efficiency is not confined to the extraction of fats; it is equally
applicable to the recovery of other products in keen demand and
commanding an attractive market price, but I select fat as an example
because it is familiar to all.
Moreover, in elaborating his fruitful thoughts the investigator is
compelled to bear in mind varying conditions. Accordingly he must
adapt his ideas to the prevailing requirements. Obviously it would be
inexpedient to concentrate perfecting effort upon one definite system.
The plant involved may necessitate a capital outlay possible only to
the wealthy firm or city, and utterly beyond the small man anxious to
embark upon such an enterprise, or be impracticable to the average
town, to which the plant, owing to the limited volume of material to be
handled, would never justify the probable expense.
In these circumstances we see plants and methods being adapted to
varying demands so that the reclamation of the urgently required fats,
oils and greases may be pursued by one and all. In a previous chapter,
describing the recovery of these commodities from the swill-tubs of
the army, I referred to one system which is wholly mechanical in its
operation. In this instance success depends essentially upon the
centrifugal turbine extractor or “whizzer,” which it must be admitted
has proved exceedingly attractive in application. For this reason the
“Iwel” system, as it is called, has met with conspicuous success and
wide application, being found in every industry.
But there is another system, or rather wide range of systems, known as
the Scott, differing entirely from the one already mentioned. This,
too, is of British origin and construction, and compels attention from
its applicability to every possible requirement as well as adaptability
to every conceivable condition, from the factory handling only a few
thousand pounds of miscellaneous fat-carrying refuse a day, to the
huge packing plants to be found upon the American continent, both
North and South, Australia and New Zealand, where the accumulations of
fresh fat are imposing, and where the necessity for prompt big-scale
treatment to secure the attractive prices ruling for high-grade fats is
so obvious. The operations of the firm under review demand additional
attention inasmuch as, through the combined efforts of its chemists and
engineers, it has been able to evolve and perfect a process which is
distinctly remarkable, seeing that it enables all but 1 per cent. of
the fat contained in the crude refuse to be reclaimed, and in such a
manner as to render the method completely profitable.
The Scott systems, fundamentally, are three in number. In the one the
waste animal products are digested with open steam in conjunction
with a vacuum; the second method comprises the _dry_ rendering of
edible fats under vacuum; while the third practice is the extraction
of the grease by what is known as the solvent system. Each possesses
its individual features, making direct appeal to the situation to
which it is most eminently adapted, and, to a certain degree, the
three respective methods may be said to represent an equal number
of progressive strides towards maximum efficiency, with the solvent
process constituting the pinnacle of success so far achieved in this
province from the simple fact that it reduces the loss of fat to 1 per
cent. absolute.
However, it is difficult to lay down any hard-and-fast rule concerning
the selection of any of these three processes because, in deciding
a question of this character, full consideration must be given to
the class of material to be handled. For instance, although the
dry rendering system under vacuum is especially applicable for the
reclamation of edible fats, it is not to say that the first, or open
steam, process is only adapted to the production of non-edible fats.
As a matter of fact there are certain classes of offal which are not
suited to dry steam rendering. The fat contained in such refuse can
be most advantageously extracted only by the open steam process.
This particularly applies to the offal produced in the large killing
establishments, where such refuse can be dealt with in the fresh
condition.
The dry steam rendering process is particularly applicable to the
production of fine or high grade edible fats. The finest fat recovered
from an animal source is that known as “Oleo” margarine or “Premier
Jus.” This is rendered from the very finest crude fat obtainable,
and in order to ensure super quality being obtained the conventional
treatment is one demanding extreme care so that its inherent qualities
may not suffer the slightest injury. The general practice is to mince
the raw material very finely and then to treat it in hot water-jacketed
pans at a very low temperature, every attention being observed to
prevent the temperature rising above a rigidly predetermined point.
In these circumstances it will readily be observed that the process
is necessarily somewhat costly and occupies appreciable time. But by
means of the dry rendering process under vacuum the raw material may
be subjected to very high temperatures, and that without the product
being impaired in any way. In fact, it is equal in every respect to
that obtained by the orthodox process, while, of course, it is far more
expeditious and cheaper.
The plant necessary to the vacuum system is simple. It comprises a
cylinder or boiler called a digester, into which the offal to be
treated is placed. Under the wet steam process and after the vessel
has been closed a vacuum is created. Open steam then is admitted into
the digester and in such a way as to enable the steam to pass upwards
through the mass, thereby thoroughly permeating it. Naturally the hot
steam renders the fat fluid, that which is free running readily to the
attached tanks.
Rendering is conducted under a pressure varying from 20 lb. to 40
lb. as the case may be, but the lower the pressure the better. The
application of the vacuum to the process constitutes the crux of the
invention. At first sight the advantages of the principle may not
be readily apparent, but they may be simply explained. In the first
instance the creation of vacuum conditions effects the removal of the
greatest obstruction to the influence of heat, namely air. If this be
eliminated cooking can be conducted at a much lower temperature than
would otherwise be practicable. Fat, indeed all animal matter, carries
a certain proportion of moisture and this must be withdrawn before
the actual release of the commodity can be effected. In vacuum water
boils at a temperature below one-half of that required at ordinary
atmospheric pressure. In other words, instead of the boiling-point
of water being 212 degrees Fahrenheit, as is the case with the
kettle on the hob, it will boil at less than 106 degrees Fahrenheit.
Consequently, if a high vacuum be established within the digester the
latent water can be converted into steam to assist in the melting
process proper, which then can be conducted unhampered. Temperature,
moreover, exercises a decisive influence upon the quality of the
product, this being very superior in quality when the recovery is
carried out at a low degree.
Another point to be noted is that all noisome odours which are thrown
off during cooking, and which cannot be avoided, are exhausted from
the vessel. They are not allowed to escape into the open air, but
are led to the furnace to be discharged into the hottest part of the
fire. They have to ascend through the incandescent fuel resting upon
the fire-bars, and, since they are not allowed to become mixed with
air, must undergo complete combustion. Consequently no pollution of
the atmosphere can possibly result from the treatment of even the most
rancid offal. It being impossible to construe the operation into a
nuisance, the plant can be installed at any convenient point even in
a densely-settled area in safety, because the system fully complies
with all the rigid requirements of the local sanitary authorities and
health officers. This is a most important feature and one which will
be readily appreciated when one recalls the insufferable conditions
precipitated by the recovery of fats and greases from refuse under the
old systems.
But the outstanding characteristic of the vacuum system is the
increased yield of fat forthcoming. No mechanical system, whether
it be pressure or high-speed whizzing, can extend completely
satisfactory efficiency results. As is well known, the fat entering
into the constitution of animal matter is contained in myriads of
minute cells which are surrounded by tissue. The walls of these cells
are exceedingly elastic and of prodigious strength. They may be
compressed to an inordinately intense degree in a press, or distorted
and stretched by recourse to centrifugal action without breaking. It
is this circumstance which reacts against a high recovery of fat by
recourse to pressing and whizzing because the cells cannot be induced
to burst.
When a vacuum is applied a totally different result is recorded. The
application of heat causes the fat and air within the tiny cells to
expand, and in this manner the walls of the cells become distended to
the limits of their elasticity. The removal of the surrounding air
within the vessel by the vacuum pump completely upsets all equilibrium.
The air pressure within the cells is higher than that applied from
without, and consequently there results an accentuated expansive effort
within the cells. But the tissue has already been stretched to its
utmost limit, and so being unable to withstand the increased strain
imposed collapses, thus releasing the imprisoned air and fat. Under the
vacuum process the disruption of the fat-carrying cells is complete,
and this explains why an augmented yield of fat is obtained by this
method.
Under the open steam vacuum process the actual practice is to apply
the vacuum three times at intervals during the operation. The first
application serves to remove the obstructive air to facilitate
and expedite cooking of the contents. The second brings about the
disruption of the cells and the release of the fat which they contain.
The third application of the vacuum, which is effected towards the end
of the process, effects the withdrawal of the foul vapours arising from
the digesting operation and their discharge into the fire.
Owing to the steam being admitted to the digester and being allowed to
come into direct contact with the mass, the residue upon withdrawal
is wet. The grease, which has been rendered fluid in the process,
has escaped from the digester through a suitable draining pipe into
a tank where settlement and clarification are carried out. But all
the grease cannot be recovered in this manner. A certain proportion,
notwithstanding the disruption of the fat cells, is held up in the
mass and can only be recovered to an appreciable degree by submitting
the residue to treatment in a press. In this way the greater part of
the remaining fat suffers expulsion and recovery. The wet cakes upon
removal from the press then have to be dried and disintegrated.
The dry vacuum process, which is essentially adapted to the rendering
of edible fat, has many advantages over the wet steam method. Whilst
the plant employed is broadly similar to that employed in the process
already described, there is one notable difference. The digester is
enveloped in an outer shell or jacket, and the steam is circulated
through the space between the two walls. It is not brought into
contact with the contents of the digester at any stage of the process.
The action taking place within the vessel during the operation is
precisely the same as when the steam is brought into direct contact
with the refuse, the fat being rendered fluid by the heat and the cells
undergoing disruption by the creation of the vacuum. A high vacuum is
maintained throughout the whole rendering process. Consequently the
moisture inherent to the raw material is withdrawn as rapidly as it is
converted into steam, resulting in the production of a fine edible fat
totally free from moisture. Moreover, the residue withdrawn from the
digester at the end of the process, known as “crackling” or “greaves,”
is likewise quite free from moisture, although, as in the case of that
resulting from the open steam process, an appreciable proportion of
fat is held up in the mass which can only be recovered to a pronounced
degree by the application of pressure.
The dry steam or jacketed vacuum process is especially adapted to
the treatment of fresh fat waste, the reclaimed product of which is
primarily intended for the preparation of edible foodstuffs, such as
oleo-margarine. By carrying out reclamation without bringing the steam
into contact with the fat several distinct advantages are obtained,
the most important being the retention of the natural properties of
the fat, and no loss of glycerine which otherwise is inevitable to a
certain degree. Consequently, it is an ideal process for the treatment
of the “Premier Jus.” There is no need to mince the fat finely, as in
the orthodox rendering process, it being necessary only to cut the
waste roughly for charging the digester.
A special press has been devised for the treatment of the crackling or
greaves. It is of the cage type which allows the fat, during pressure,
and which operation is carried out while the residue is very hot, to
be expressed between the bars of the cage to fall into a trough for
recovery. The cakes, after pressing, are dry, excellent in quality,
light in colour and of attractive flavour, a result due to the fact
that the tissues have not been scorched or charred in any way during
the rendering process. The greaves constitute an excellent ingredient
for the preparation of kennel and poultry foods, and enter extensively
into the manufacture of dog-cakes. In a few instances the dry greaves,
owing to their high nutritive value, are served to the kennel in the
straight form as they issue from the press.
While the dry vacuum process is certainly efficient, it does not
fully comply with the latest ideas pertaining to the recovery of fats
from organic waste. The press is the weak link, because thereby it is
only possible to recover a certain proportion of the fat held up in
the mass, even when the cellular construction has been completely
broken up. It is stated, as a result of accumulated experience, that
the amount of fat left in the greaves may run up to as high as 10 per
cent. of the original fatty content of the offal: in many instances
it has been found to range as high as 20 per cent. The fact that this
remaining fat defying reclamation by pressing must be relatively high
is evident from the readiness with which certain waste exploiters will
buy up the greaves, not to turn them into kennel and poultry foods, but
to submit them to further treatment in order to wring out still more of
the fat which they carry.
This manifestation of enterprise has been rendered possible by the
advance of the science of fat recovery from offal to such a level as to
enable 9 per cent. of the fat remaining in a 10 per cent. greaves to
be extracted. It is the prevailing high price commanded by fats which
renders such additional treatment upon an extensive scale so attractive
and eminently profitable.
The process in question is the Scott solvent recovery invention to
which I have referred, and which represents the greatest achievement
yet recorded in the whole science of fat reclamation from organic
waste. The process was perfected and patented shortly before the war,
and although hostilities militated against its immediate and rapid
development, thereby delaying the recognition of its overwhelming
virtues, it is satisfactory to learn that many plants operating upon
this principle have been laid down, not only in this country, but in
other parts of the world. It is the process which at the moment is
arousing the most intense interest, owing to the progressive stride
which it represents in this field.
The process is delightfully simple, although apparently it involves an
intricate plant and demands a higher level of skilled labour, but where
the work of reclamation is conducted along ambitious lines it cannot be
excelled. Briefly described, it turns upon the employment of benzine,
or some other equally volatile solvent which, as we all know, will
readily dissolve fat and absorb it. What can be done with this agent is
familiar to every housewife who practises the removal of grease spots
and other unsightly marks from clothing by the aid of benzine, while it
is the medium whereby dry-cleaning is rendered practicable.
The raw material--condemned meat, offal and other organs of the animal
recovered from the slaughter-house which possess no edible value--is
charged into a steam-jacketed horizontal extractor fitted with stirring
gear. When condemned carcasses are to be treated there is no need
to carry out preliminary deboning; it is merely necessary to reduce
the material to rough pieces for convenience of handling. It will be
observed that the steam is not brought into contact with the mass, but
is circulated through the jacket as in the dry vacuum process.
The solvent is introduced in the first instance in the form of
vapour, being passed through boxes of special construction, to pass
finally into the extractor. The contents of the latter being in a
condition of constant agitation as a result of the manipulation of the
stirring gear, the benzine vapour is able to permeate the mass. The
heat radiated from the steam circulating through the jacket converts
the moisture present in the material into vapour and with which the
solvent comes into contact. Vaporization of the moisture causes the
solvent itself to condense to a certain degree, and in the liquid form
it dissolves out the grease. The process is continued until the bulk
of the moisture has been eliminated, when the grease and solvent are
withdrawn. When the grease has been fully extracted down to a limit
which will result in a dry meat-meal, containing about 1 per cent. of
grease, the benzine is steamed off in the usual manner. The benzine
itself is recovered because it is only permitted to work in a closed
circuit, and, after fulfilling its purpose, is passed to a still to be
cleaned and purified, after which it is again passed to the extractor
to repeat the cycle of operation.
The process, it will be observed, is continuous, while the benzine
may be used over and over again. All that is required is to place
a sufficient quantity of the solvent into the circuit to carry
out the operation with the essential efficiency. Naturally, the
quantity involved varies with the size of the plant and the work to
be fulfilled, but it may run up to 5,000 or more gallons. The plant
is generally laid out upon the unit principle, which is the most
satisfactory, because it facilitates the adaptation of the installation
to the volume of work in hand. One or more units can be shut down
during the “off” period, allowing the remainder to be worked up to
their full capacity, which, of course, is the most efficient and
economical method. The losses of benzine are very low--not exceeding
1 per cent. of the weight of the raw material treated. In fact, there
are many installations in operation where, over a period of one year,
the benzine loss recorded is actually below 1 per cent. This factor is
vitally influenced by the care and attention bestowed upon the plant.
If it be carefully tended, all joints being kept in the tightly packed
condition, and the condenser maintained in a high degree of efficiency,
the benzine loss may be reduced to an infinitesimal degree, the value
thereof representing but an insignificant fraction of the value of the
increased yield of oil and fat.
The solvent acts upon the grease only. It does not affect in any way
the gelatinous material, and, consequently, the nitrogenous or ammonia
value of the ultimate meal is considerably enhanced as compared with
the results achieved with the digesting plant. The meal is discharged
from the extractor in a dry crisp condition ready for immediate
grinding, and is admirably adapted for poultry and cattle feeding. No
traces of the benzine remain.
The bones may be ground immediately, if desired, but if these should
be forthcoming in sufficient quantity they should be passed on to the
glue and gelatine plant. There is no necessity to submit them to a
further degreasing process, because this has been completed in the one
operation in the extractor. As a rule, however, with installations
devoted to the treatment of condemned meat and other offal, the bones
are not forthcoming in sufficient quantities to justify the attachment
of a glue recovery plant although, of course, they can be sold to other
works specializing in this work. It is merely a question as to whether
it would pay to transport the degreased bones to the glue works. If
not, they can be ground up to be utilized as fertilizer, for which, it
is needless to say, a good price can be obtained.
The recovery of fat down to 1 per cent. of that contained in the crude
material does not constitute the only outstanding advantage of the
solvent extraction process. It enables the whole of the operations
to be condensed into one task, completely dispensing with all
auxiliary apparatus. The refuse is merely charged into the extractor
and withdrawn in the form of powder, and, if condemned carcasses
have been exploited, bone as well. What this means may readily be
realized. Under the open steam digesting system--even with the wet
and dry vacuum systems to a lesser degree--the refuse must first be
cooked. The material upon withdrawal from the digester must be passed
through the press, after which treatment it has to be disintegrated
and dried. If the reclamation of the gelatinous or “stick” liquor, as
it is called, be part of the process this also demands handling. Thus
one may safely anticipate having to conform with five distinct and
separate operations, involving intermediate handling and supplementary
plant, while the loss of fat in passing from stage to stage is far
heavier than may possibly be imagined. But, with the solvent extraction
process, the numerous above-mentioned operations are resolved into
one, and one only--the charging of the extractor with the refuse. The
saving in labour by the elimination of all interhandling is obvious,
which in these days of enhanced wage costs demands consideration, while
there are no intermediate losses of oil. In so far as saving of time
is concerned there is little, if any, difference. Under the solvent
extraction method a period of eight to ten hours is required to deal
completely with a charge of 4,500 to 9,000 lb.
The fruits accruing from this latest manifestation of ingenuity in
connection with the reclamation of waste may be tersely emphasized.
The reclamation of the fat down to 1 per cent. being accepted, it may
also prove interesting to indicate how effectively the nitrogenous or
ammonia value of the product is preserved. The following represents
a typical analysis of a meat meal, which, it should be pointed out,
contains no bone whatever. The figures are:--
Per cent.
Tribasic phosphate of lime (superphosphate) 3·25
Nitrogen 11·37
⤷
= ammonia 13·81
At the large cattle-slaughtering establishments of North and South
America, and at the sheep-killing stations in Australia and New
Zealand, the residues from which the edible fat has been recovered
by the open steam process are turned over to the solvent extraction
plants which have now been introduced to form an integral part of
the waste-recovery system, the value of the invention being fully
appreciated. At first the practice was to dry the residues from the
digesters before committing them to the extraction plant, but since
it was found superfluous to carry out such a preliminary, the residue
is turned over from the open steam digester where the edible fats are
obtained to the solvent extraction plant, the idea of course being to
secure the proportion of fat escaping recovery in the digester. In
this manner 99 per cent. of the fat contained in the crude waste is
obtained, but the proportion reclaimed from the practice of the solvent
extraction process is set aside for manufacturing purposes--conversion
into soap and other utilitarian commodities.
In the course of digesting the fresh fat with open steam a considerable
quantity of the “stick” liquor is precipitated, and its recovery for
size is fully justified. In the crude form this liquor is somewhat
weak, but by means of the Scott multiple-effect vacuum evaporating
plant it can be concentrated to any required degree of density. This
product is blended with the meat-meal from the solvent extraction plant
in a suitable vessel and is then dried to a powder, the ultimate meal
being high in ammonia.
In the case of the offal which is not suitable for the production of
an edible fat, recourse to the open steam digester is eliminated.
The refuse, along with the condemned meat, is consigned directly to
the extraction plant to be dealt with in one operation. A similar
practice is followed at the large pig-killing establishments. At
one installation in South America, where there is an impressive
illustration of British ingenuity and enterprise in regard to
waste recovery upon the Scott principle, the tallow produced is
immediately dispatched to the adjoining soap works--also a British
installation--where the glycerine is recovered and soap is produced. In
this instance therefore we have a powerful example of a self-contained
establishment completely equipped for the recovery of the whole of the
by-products incurred in the course of its normal operations and to the
utmost advantage.
The Germans have been extremely active in advancing the possibilities
of the solvent extraction process. Several large plants are in
operation in the Fatherland, of which we heard a good deal during
the war, but the character of the operations of which were grossly
misrepresented and exaggerated. Those behind the lines were reserved
exclusively for the disposal of fallen horses as well as the offal
and other wastes resulting from the feeding of the troops. The fat,
immediately upon its extraction, was treated for its glycerine, which
was dispatched to the explosive manufactories in Germany, while the
residues were converted into soap upon the spot. This practice was
followed because the glycerine was the staple in most urgent demand,
and the transport of which was far simpler than the movement of the
crude reclaimed fats. So far as soap was concerned the German soldiers,
even up to the front lines, had little or no room for complaint, for
the simple reason that it was prepared in their midst at the plants
which were installed within easy access of the centres of suitable raw
material supply.
British manufacturers, although somewhat conservative, are becoming
alive to the fact that only by the solvent extraction process can
the utmost wealth be won from fats derived from waste materials, and
many interesting expressions of enterprise in this direction may be
recorded. For instance, the manufacture of maize flour has made decided
strides in these islands during the past five years, doubtless owing
to the deficiency in connection with the wheaten product. However,
before this grain can be converted into the farinaceous form the germ
must be extracted, otherwise the keeping qualities of the flour are
seriously impaired. But, seeing that the germ represents approximately
20 per cent. of the whole grain, it will be seen that the industry
has to face a loss of one-fifth of its raw material in preparing the
flour--an imposing quantity. However, the germ is rich in oil, this
constituting approximately 20 per cent. of its bulk. The demand for
oil, particularly those of vegetable origin, is such that the maize
germ, instead of being turned over directly to cattle, is now being
exploited for its oil. By the solvent extraction process 99 per cent.
of this available 20 per cent. of oil is being extracted, the resultant
meal thus being virtually free of oil.
When the idea was first taken in hand it was maintained that the
withdrawal of the oil would imperil the feeding qualities of the meal
residue. This being conclusively disproved it was then argued that the
employment of benzine for the purpose would depreciate its cattle-food
value, the idea doubtless being entertained that it must be associated
with a certain benzine flavour from coming into contact with the
solvent. But here again practice did not coincide with precept, because
horses will devour the meal, freshly drawn from the extractor, with
avidity, and look round for more, proving very convincingly that
the benzine is completely exhausted from the extractor after having
fulfilled its designed function. Experience has shown that meal made
from the de-oiled maize germ is every whit as good and as nourishing
as, if not actually superior to, that which has not been subjected to
the oil-recovery process.
The solvent extraction process has proved to be of incalculable value
to the firms specializing in the dry-cleaning of clothes, fabrics,
and textiles in general. When the articles are likely to be charged
with appreciable quantities of dirt, such as carpets, they are first
subjected to a dusting treatment which removes the superfluous or free
dirt. Wearing apparel, except in a few instances, does not require
submission to this preliminary operation and so is passed into the
washing machine, which contains only benzine, together with a slight
proportion of ammoniacal liquor. The garments are passed through
several successive washings and rinsings in various machines, to be
submitted finally to the hydro-extractor, where practically the whole
of the benzine is recovered, the goods being delivered practically dry.
But to be positive upon this point they are hung for three or four
hours in a drying room. The articles are then examined for any stains,
such as blood and grease marks, which have resisted elimination in the
mechanical cleaning process. These are removed by hand--“hand-spotting”
as it is called, either with water, or with benzine and a little
soluble soap and a brush.
The dirt and other deleterious matter removed by the benzine in the
washing and rinsing machines is separated from the solvent, which
undergoes a simple treatment, bringing about its complete purification,
when it is returned to the service-tanks for further use. The process
is one of continuous distillation, the benzine, as previously
mentioned, being used over and over again, it only being necessary to
add certain quantities from time to time to remedy the unavoidable
losses incurred. The wastage of benzine averages about 15 per cent.
of the weight of the goods treated. Seeing that about 4,500 gallons
may pass hourly through the machines and the circuit, the loss is
relatively low. The quantity of dirt removed, despite the thoroughness
of the process, is comparatively trifling.
One interesting phase of the dry-cleaning process deserves mention,
if only to bring home the assiduity with which the reclamation of
grease from every conceivable source is now being prosecuted. Some
of the firms are devoting attention to the separation of the grease
removed from the clothes by the benzine. Seeing that the only likely
contribution of grease is that removed from the hands or other part
of the body coming into contact with the fabric, and that the grease
in question is only natural perspiration, it will be seen that, under
the most favourable conditions, such deposit must necessarily be
exceedingly trifling. That it should be deemed worthy of recovery seems
almost incredible. But it is being done, though the yield is low, and
it is proving profitable.
Probably no other waste is to be found in such a multiplicity of forms
and in such unexpected quarters as that capable of yielding grease, but
that it should pay to recover natural perspiration to assist in the
lubrication of a railway locomotive, or some other piece of machinery,
serves to emphasize the extremely fine limits to which fat-reclamation
science has been carried. It is admitted that, in the majority of
cases, the possible yields are so small as to render reclamation
absolutely impossible by any but the solvent extraction process, which
undoubtedly constitutes the highest testimony to the efficiency and
value of this wonderful British invention it is possible to advance.