Millions from Waste by Frederick Arthur Ambrose Talbot - HTML preview

CHAPTER V
 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:—

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.