text: House-broken animals, such as cats, are trained into the habit of urinating and defecating in a specially provided litter box. Similarly, untrained and caged animals, such as guinea pigs, urinate and defecate on the floor of their cage, often in approximately the same floor area of the cage. Consequently, pet owners, homeowners, veterinarians and laboratory personnel have added absorbent materials to the litter box or cage to collect the urine and feces. After a relatively short period of time, the dross-soiled absorbent emits objectionable odors because of the presence of the urine and fecal matter.
  In order to reduce or eliminate these objectionable odors, homeowners periodically remove the fecal matter from the litter absorbent physically. However, physical removal of the feces does not reduce or eliminate odors caused by the urine absorbed into the absorbent. Therefore, when the odors caused by the absorbed urine become intolerable, the homeowner discards the litter box absorbent material entirely. The homeowner then washes the litter box and refills the litter box with fresh litter box absorbent material. These activities are unpleasant, time-consuming and expensive. Consequently, the litter box absorbent material usually is a relatively inexpensive solid absorbent material, such that an individual cleaning of the litter box is not particularly economically burdensome. However, repeated litter box cleanings over a period of time accounts for relatively large expenditures.
  The most commonly used litter box absorbent materials are inexpensive clays, such as calcined clays, that are safe and non-irritating to the animals, and that absorb relatively substantial amounts of liquids. Other porous, solid litter box absorbent materials, that are used alone or in combination, include straw, sawdust, wood chips, wood shavings, porous polymeric beads, shredded paper, sand, bark, cloth, ground corn husks, cellulose, and water-insoluble inorganic salts, such as calcium sulfate. Each of these absorbent materials has the advantage of low cost, but each suffers from the disadvantage of merely absorbing a liquid waste product and holding the product within its porous matrices, or, in the case of sand, adsorbing the liquid dross on its surface. For each absorbent material, offensive odors are eventually caused by the absorbed urine, and the entire contents of the litter box, including soiled absorbent material and unsoiled absorbent material, has to be discarded.
  One such litter box absorbent material is described in Lohman U.S. Pat. No. 4,570,573. The Lohman patent is directed to an animal litter composition comprising about 60-94% by weight paper, about 1-35% calcium sulfate and about 3-12% water. Such an absorbent is effective in collecting animal dross, but it does not reduce or eliminate the generation of objectionable odors and does not eliminate the disadvantage of periodically replacing the entire contents of the litter box. Larson et al in U.S. Pat. No. 4,315,761 describes the use of aerated or foaming concrete, of relatively large size, like up to 10 mm (millimeters), to absorb animal dross and facilitate removal of the excrement from a litter box. The aerated concrete merely absorbs the animal dross, and therefore suffers from the identical drawback of present day animal litter box compounds, i.e., an inability to easily separate the soiled absorbent particles from the unsoiled absorbent particles without having to clear and clean the entire litter box.
  Stuart, in U.S. Pat. No. 4,685,420, disclosed an improved litter box absorbent composition comprising from 0.01% to 5.0% by weight of a water-absorbing polyacrylate in combination with a common litter box absorbent material. According to the method and composition of Stuart, the polyacrylate and absorbent material absorb the urine or similar waste material, and the polyacrylates act to gel the soiled litter box absorbent material into a gelled product. Stuart teaches that the gelled absorbent material then can be physically removed from the litter box to reduce the generation of offensive odors, and to avoid discarding the unsoiled portion of the absorbent material. However, the method and composition of Stuart suffers from the disadvantage of relative cost ineffectiveness. The commonly used litter box absorbent materials are very inexpensive materials, whereas the water-absorbent polymers of Stuart are relatively expensive products that can raise the initial cost of the litter box absorbent material to an unacceptable level in a very cost competitive market.
  Other litter box absorbent materials are disclosed by Fisher in U.S. Pat. No. 3,765,371 describing a foamed plastic for absorbing and/or adsorbing animal dross; by Kramer et al in U.S. Pat. Nos. 4,275,684 and 4,395,357 describing calcium silicate as an animal litter box absorbent material and specifically teaching against the use of mineral products, such as clay-type minerals, because of the mineral product's tendency to swell upon liquid absorption; by Rodriguez et al in U.S. Pat. No. 4,494,481 describing the addition of a .[.transmition.]. .Iadd.transition .Iaddend.metal of Group Ib or IIb of the periodic table to present-day litter box absorbent materials to prevent the development of urine odors; and by Greenberg in U.S. Pat. No. 4,638,763 describing the addition of sodium sulfate to a litter box absorbent material to facilitate removal of soiled absorbent from the litter box.
  Therefore, a need exists for a litter box absorbent material that effectively collects the urine or other dross material of house-broken pets and caged animals; that agglomerates when wetted to allow physical removal of the wetted litter box absorbent material from unwetted litter box absorbent material in order to reduce or eliminate dross-based odors and to reduce costs associated with animal litter box absorbent materials; and that is sufficiently economical for practical use in a highly competitive and cost conscious market. Surprisingly and unexpectedly, it has been found that water-swellable bentonite clays effectively absorb animal dross; and during absorption of the animal dross, agglomerate into a sufficiently large and stable mass for physical separation of the soiled portion of the litter box absorbent material from the unused portion of the litter box absorbent material. The water-swellable bentonite clays, and their absorbent and agglomerating properties, effectively reduce or eliminate odors associated with animal dross; reduce costs associated with litter box absorbent material replacement; and are sufficiently economical to compete effectively in a highly competitive and cost conscious industry.