been abandoned. Fuller's earth is also said to be used in the manufacture of pigments for printing wall paper, in detecting certain coloring matters in some food products, as a substitute for talcum powder, and in medicine as a poultice and as an antidote for alkaloid poisons. Another suggested use is in deliming hides in the manufacture of leather. It has also been stated that the fuller's earth cake from oil mills can be used in the manufacture of hand soaps, concrete, waterproofing, and asphalt preparations.1

As of general interest the following is quoted from an article by Maynard and Mallory 2:

Fuller's earth can be defined as a highly siliceous clay, usually indurated, which has the property of adsorbing certain organic coloring matters from vegetable and mineral oils. This property, which defines the earth and is indicative of its value, can be determined only by actually filtering the oil in the laboratory.

The American earths have been found more desirable for the refining of petroleum, while the English earth has been regarded as better adapted for the bleaching of edible oils. American earths have been found of distinctly superior bleaching power to English earth with the vegetable oils as well, but they have failed to displace the English earth on account of the dependable uniformity of the imported earth, thus assuring the refiner a standard of bleach, uniform filtering, and reliably low oil-retention properties.

Very little has been published regarding the treatment and preparation of the English earth, but it has recently been determined by the writers that certain of the American earths can be commercially prepared, so that the bleaching properties, filtering, and oil adsorption are equally as dependable and these qualities found more desirable than those of the English earth.

Fuller's earth is characterized by its light weight, due to the proportion and nature of the pore space. Sand in varying amounts is usually present as well as some mica and in places calcium carbonate in the form of fragments of shells. The earth is conchoidal in fracture, usually indurated, and does not slake in water. It is brittle and not plastic until ground. The earth varies in color from gray to blue, and brown to greenish and yellow. The yellow earth has passed through extreme processes of oxidation, and in some areas the yellow oxidized earth proves to be of superior bleach.

Although fuller's earth has a true specific gravity about equal to that of other clays, it is so porous in nature that when thoroughly dry most samples will float in water, showing the presence of more than 50 per cent voids.

Chemical analyses have never been regarded as of any particular value in arriving at an interpretation of the possible value of the earth for commercial use. An ultimate analysis, beyond showing the quantity of possibly objectionable impurities as lime and pyrite, is without much meaning. A determination of hydrous silica and of the aluminum silicates, which would in effect constitute the colloidal content, often may be of direct value.

The total silica in different earths may vary from less than 50 per cent to even more than 80 per cent; the alumina is always low, usually from 5 to 20 per cent; the combined water, from 5 to 12 per cent, is about that of the more siliceous clays. These are the more important constituents, and any others may be considered as adulterants, sometimes harmful. Lime and magnesia are nearly always present, and the iron content is usually evidence of secondary enrichment. The alkalies in many of the commercial earths do not total more than 1 per cent. The mechanically carried water (moisture) is high, even more so than in most clays, and there is the same tendency to absorb moisture in storage.

The bleaching power of fuller's earth is the basis of its commercial use. Several theories have been put forward to explain this action. Like many other colloid peculiarities, it is due to a combination of mechanical and electrical properties, with chemical action eliminated from consideration only by nice

1 Chem. and Met. Eng., vol. 26, No. 13, p. 602, March 29, 1922.

2 Maynard, T. P., and Mallory, L. E., Commercial preparation and use of fuller's earth: Chem, and Met. Eng., vol. 26, No. 23, pp. 1074-1076, June 7, 1922.

differentiation. It is a combination of adsorption and mechanical filtration, accompanied by some chemical disintegration due to selective adsorption.

The active constituents of the earth are probably hydrous silica and hydrous aluminum silicates. The porous nature of the earth, due to the fact that it is built up of grains approaching colloidal size, offers a large active surface.

The driving off of the combined water does not directly affect the bleaching properties of the earth, but this may require temperatures that will destroy a portion of this power by a reduction in surface as the clinkering stage is reached. Coarsely ground earths used in the bleaching of petroleum oils are not affected in their bleaching properties when the water of combination is driven off, while the very finely divided earths used in the bleaching of vegetable oils have their bleach more materially injured by driving off the combined water.

A few earths can be used for bleaching both mineral and vegetable oils, while most of the earths are by nature limited to one field or the other. In the bleaching of mineral oils an earth of high specific volume is more in demand, while in the refining of vegetable oils earths of lower specific volume are more desirable.

The methods of preparation of earth for the bleaching of mineral oils and vegetable oils are quite different. The preparation of the earth for the bleaching of mineral oils is much nearer standardization.

The earth is graded by size of particles for bleaching mineral oils according to the nature of the oil to be treated. The more common gradings are 30 to 60 and 60 to 80 mesh, while there is some demand for 15 to 30 and minus 80 mesh. The earth is burned at a low heat to remove moisture and combined water and then placed in large cylindrical containers. The oil is percolated through under pressure, if necessary. When the oil runs too dark the earth is washed as free of oil as practicable and burned in rotary kilns. The number of times an earth may be reused depends mostly upon the resistance that it shows to breaking down in burning and handling; with 25 to 30 per cent loss the earth is reused as much as 10 times. The quantity of oil bleached by a ton of earth, of course, varies widely; with medium oils a total of 250 barrels per ton of earth is good practice.

In the refining of vegetable oils the crude oil is heated and treated with an alkali to remove the fatty acids and convert the coloring matter to the basic form. The oil is usually bleached at approaching the boiling point of water by stirring in from 1 to 5 per cent of the earth. Moisture, either in the earth or in the oil, interferes with the process. The hot oil, with the fuller's earth in suspension, is then forced through a filter press. Following this the oil is put through a deodorizing process. The refining then varies, depending on the use to which the oil is to be put and upon the particular process of manufacture. Some processes include a second bleaching with a mixture of fuller's earth and carbon black. The oil usually starts the bleach with slightly alkaline reaction and finishes the process somewhat acid.

The amount of earth used, from 1 to 5 per cent, is determined by laboratory control for the bleach required. The filter cake is usually washed with steam, hot water, air, or various combinations of these. The cake is then wasted with any retained oil. As the earth tends to oxidize the oil, the cake must regularly and carefully be disposed of. Some earths can not be used, as they oxidize the oil so rapidly that it takes fire in the presses.

The earth is prepared by drying and grinding 70 to 100 per cent through 200 mesh for the vegetable oil bleach. This fineness of grinding depends, or should depend, upon the producer's understanding of the individual characteristics of his earth. A finely porous earth requires less grinding to develop the necessary bleaching surface. The grinding is further limited by the behavior of the earth in the bleaching kettles, in the pumps, and in the filter presses. Furthermore, each earth possesses a natural limit in bleach beyond which it requires much more than a relative increase in bleaching surface, whether by finer grinding or an increased percentage of earth, to obtain another point or two in bleach. A little calculation makes this understandable. One pound of commercial fuller's earth offers a bleaching surface of several hundred square feet. Six per cent of this earth thoroughly stirred through the oil gives an oil film thin enough to compare closely with recently determined films of lubricating oils. The effectiveness of the earth at this concentration should be rapidly approaching a limit.

Fuller's earth found its first commercial use in removing oil from woolen cloth. This property of absorbing oil is inherent in the earth.

* * * Oil losses in filtering vegetable oils run from 15 per cent of the weight of the earth used to more than 30 per cent. At the lower figure they exceed in cost the value of the fuller's earth. The refiner endeavors to reduce the losses of oil by scouring the cake and experimenting to find commercial means of recovery. The producer can bring his brand of earth into favor by lowering the oil losses with his earth as much as is practicable.

These losses may be divided into three more or less determinate parts-(1) loss in oil film, (2) loss by absorption in the pores of the earth, (3) loss in small and inaccessible voids between the particles.

In a well-washed cake the loss in oil film should not amount to more than 10 per cent of the total loss; the loss by absorption of pores in the earth is a property of the individual earth, though it can often be lessened by proper grinding; the third and often largest factor can be regulated more directly, although a separate problem for each type of earth. The use of the best adapted system of grinding or the proper combination of two or more systems of grinding makes possible the grading of particles that will reduce these inaccessible voids in the cake to a minimum, while in no way interfering with the filtering properties of the earth.

The authors have recently put through a wide series of commercial tests on certain earths with oil losses markedly lower than with other earths and with bleaching properties superior to those of the standard English earth.

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66

There is a possibility of a widening market in making cheap "clay pigments' due to the property of fuller's earth of strongly adsorbing basic dyes. The property of adsorbing bases gives it a real value as a commercial and simple water softener." The earth when freed of sand and properly ground is in good standing as a filler, particularly in the rubber trade. The "fines now wasted in the preparation of the earths for the mineral-oil trades may be utilized by further preparation for the uses above mentioned.

Carbon blacks, calcined bauxite, prepared lignite, and infusorial earth are also used in the refining of oils and sirups. It is possible that fuller's earth under modifications of present processes, where necessary and practical, may replace some of these materials.

In arriving at the possible value of an undeveloped earth a geological interpretation of its origin is of primary importance. Determination by chemical analysis of hydrous silica and aluminum silicates may have scientific value in predicting bleaching quality.

A relative determination of bleaching surface due to porosity may be made by comparing the bleaching power of an earth at different finenesses. This may be used as a base to determine nature of grinding required not only to develop bleach but also to control oil absorption.

Commercially feasible developments are dependent on location with respect to transportation, inherent superior qualities of the earth, preparation that develops these natural advantages for a particular market, and then technical control of the product. Only by a combination of these essentials can a reliable, uniform, dependable, superior commercial earth be prepared.

Our investigations show that while American earths of superior bleach to standard English earth are on the market, yet the excessive oil retention of these earths resulting from a lack of proper grinding and technical control have prevented them from occupying the position they should have.

Earths of dependable uniformity are available and eminently satisfactory to the mineral-oil refineries. However, the large amount of "fines" resulting from grinding and which can not be used by this trade, and which materials are now largely wasted, can be utilized and established in other trades by their proper preparation, at values equal to the earth shipped to the oil refineries. The present losses are wasteful and inexcusable.

While the markets and the value of fuller's earth have been growing rapidly, the producer of the mineral-oil [bleach] on the one hand has paid little attention to his by-product in the way of "fines" and the producer of the vegetableoil bleach on the other hand has not developed the all-around desirable earth that his market demands.

With the growing knowledge of the needs of the industries, technical control of production is the next step in development and will lead to markets other. wise beyond attainment or even conception.

HISTORY

3

Fuller's earth was first discovered in the United States in 1891 near Alexander, Ark., by John Olsen. This earth was used for a time by the Southern Cotton Oil Co., at Little Rock, Ark., but its use was finally abandoned. The real beginning of the industry in this country was, however, in 1893 near Quincy, Fla., when quite by accident, in an unsuccessful effort to burn brick on the property of the Owl Cigar Co., an employee called attention to the close resemblance between the clay used and the German fuller's earth. This discovery in Florida caused considerable excitement, and deposits of fuller's earth were reported from a number of States, but the material in most of these deposits was found to have no value as fuller's earth. Production began in Florida almost immediately after the discovery, and in 1897-1899 fuller's earth was produced in Florida, Colorado, New York, and Utah, with Florida the leading producer, a rank that it has maintained continuously. In 1901 Arkansas again became a producer. From 1904 to 1907 Arkansas was the second largest producer. Fuller's earth was found in Georgia soon after its discovery in Florida, but Georgia did not become a producer until 1907, when it was the third largest producing State, and it has ranked second since 1909, except in 1918 and 1919, when Texas was second. In 1904 Alabama and Massachusetts, in 1907 South Carolina and Texas, in 1909 California, in 1918 Nevada, and in 1922 Illinois and Pennsylvania first appeared as producers.

The small number of producers in some States makes it impossible to publish totals for those States without disclosing individual operations. Nearly all the earth produced in 1923 came from the Southern States. Two operators reported in Illinois, and one reported in Massachusetts. Florida was the leading State, Georgia was second, and Texas was third, as for a number of years. These three States reported 92 per cent of the output in 1923, compared with 97 per cent in 1922. Illinois was fourth, Massachusetts fifth, and Alabama sixth. The outstanding features of the industry in 1923 were the decrease in production in Florida and Georgia and the increase in production in Illinois, by the addition of a new plant, and in Texas.

Branner, J. C., An early discovery of fuller's earth in Arkansas: Am. Inst. Min. Eng. Trans., vol. 43, pp. 520-522, 1913.

FIGURE 8.-Production, total value, and average value per ton of fuller's earth, 1895–1923.

IMPORTS

The imports of fuller's earth, which at one time constituted the entire supply, were increasing before the World War and reached their maximum in 1914. Since 1914, except in 1917, 1920, and 1922, there has been a steady decline in imports, the quantity in 1923 being the lowest in more than 25 years. Owing, however, to the higher prices prevailing in later years the value of the imports in 1923 was not so low comparatively but was the lowest since 1909. Wrought or manufactured earth represented in 1923 about 93 per cent of the quantity and value of imports.

Fuller's earth imported and entered for consumption in the United States, 1917-1923

DOLLARS