as noted above , the present invention is a washcloth or other personal hygiene items that is treated with a temperature changing compound that changes the temperature of the device when contacted with water . for the purposes of this invention , the term “ washcloth ” includes any item that is used by persons to wash or clean some object . it is not intended that the application be limited to cleansing personal bodies . typical fabrics for this invention are those that are normally used to make washcloths and other cleansing cloths or related items . by way of example and not as a limitation , fabrics include cotton , blended fiber fabrics , and some forms of cellulose fibers such as paper . one example of paper is the heavy paper used in paper towels , particularly those that are more absorbent . other fabrics are known as nonwoven fabrics . one example of a nonwoven fabric is , of course , paper , but other fibers are also contemplated by this invention without limitation . the invention is not limited by the choice of fabric as long as the fabric is capable of receiving dry temperature changing compounds and retaining them for reaction when water is brought in contact with the compound . since the device of this invention is normally used once , when water contacts the embedded temperature changing compound to produce heating or cooling , the less expensive fabrics are more economically desirable . often the device is discarded after that single use , though it may still function as a useful cloth other than being self - heating or cooling . the preferred heat generating material is a crystal formed from several components that , when free from moisture , are stable for up to three to five years or more , and which react when moisture is present to generate heat . the preferred crystal is made from a crystalline mixture of calcium oxide . calcium oxide is commercially available from a number of sources , one of which being calcium oxide fisher scientific s79946 . for efficient integration of this component into the fabric , the calcium oxide is ground into small particles or crystals and a sieve is used to insure uniform particle size . in some instances it is also desirable to add citric acid that functions as a heat sink to regulated the rate of reaction and to react with the hydrated calcium oxide , the citric acid is also commercially available from a number of sources . one source of citric acid is sigma aldrich 201 - 069 - 1 . in the most preferred mixture of the heat generating material is a mixture of calcium oxide with a zeolite powder . more than 150 zeolite types have been synthesized and 48 naturally occurring zeolites are known . they are basically hydrated alumino - silicate minerals with an “ open ” structure that can accommodate a wide variety of positive ions , such as na + , k + , ca 2 + , mg 2 + and others . these positive ions are rather loosely held and can readily be exchanged for others in a contact solution . some of the more common mineral zeolites are : analcime , chabazite , heulandite , natrolite , phillipsite , and stilbite . an example mineral formula is : na 2 al 2 si 3 o 10 - 16h 2 o . preferred is a ratio of calcium oxide to powdered zeolite of from about 14 to 20 for calcium oxide and from about 7 to 10 for powdered zeolite . most preferred is a ratio of calcium oxide to powdered zeolite is 17 :: 8 . 5 . the heat generation material most preferred , using the above components includes a calcined calcium oxide . this material is available as a small article size , with a diameter less than about 0 . 2 mm , and as a particle of somewhere between 0 . 2 and 0 . 8 mm . larger particles are ground and smaller ones sieved , and the calcium oxide is then calcined . it has been found to be effective to calcine for at least 60 to 120 minutes , and preferably about 90 minutes , at temperatures above 500 ° c ., and most preferably at about 550 ° c . for that period of time . the calcined calcium oxide is , of course , desiccated to prevent any contamination by moisture . laboratory grade citric acid and powdered zeolite are mixed with the calcium oxide in moisture free conditions , in an appropriate reaction ratio to provide the exothermic reaction upon contact by the activating agent water . in a preferred embodiment , the heat generation material also includes a small quantity of polyalkyl glycol such as polyethylene glycol or similar materials which are used to coat the calcium oxide prior to initiating the exothermic reaction . this small coating , of 1 % to 7 % polyethylene glycol by weight in the total composition slows down the reaction with water to prolong the heat for over two hours . a preferred weight percent of polyethylene glycol is from 3 % to 4 %. tests have been made that kept a container of one liter of water at a temperature of 140 ° f . to 165 ° f . for more than two hours . while this is a long time for a wash cloth to remain hot , extending the reaction time at least for as long as needed to complete personal hygiene practices is of considerable value . it is also an embodiment of the present invention to employ a temperature changing chemical that causes a drop in temperature when contacted by water , creating an endothermic reaction . the solid materials may , for example , include materials such as sodium sulfate * 10h 2 o ; sodium bicarbonate , ammonium nitrate , ammonium chloride , urea , ammonium dichromate , citric acid , potassium perchlorate , potassium sulfate , potassium chloride , calcium nitrate , and vanillin . these solid compounds react with water in an endothermic fashion to impart cooling . reactions can be with water based mixtures as well as other liquid systems . again these materials should be small in size so the crystals can be embedded into the fabric on which they are deposited . the process of embedding the temperature changing chemical simply involves placing the desired amount of chemical on a ply of the fabric and pressing the chemical into the fibers of the fabric . the embedded surface is then covered by at least one additional ply of the fabric . when the embedding is done with a calendar device , the fabric containing the chemical on its surface can pass through the rollers directly . alternatively , a second ply ( or more ) can be placed on the surface with the chemicals , either embedding the crystals into both plies , or into the first ply if the second ply surface is less penetrable . although the present invention has been described with reference to preferred embodiments , workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention .
a washcloth or other personal hygiene cloth having an adjustable temperature when used . a first ply of fabric has a dry temperature changing chemical embedded on it to form an embedded surface and at least one additional ply of fabric is placed to cover the embedded surface . the addition of water to the device causes the dry temperature changing chemical to change the temperature of the washcloth device . the temperature changing chemical can be one that heats or one that cools the washcloth . more plies may be added to increase the thickness of the device .