acids which are useful in preventing the accumulation of gaseous ammonia are defined by four criteria : the molecular weight per acid functionality should be low so that only a small amount of acid will be needed to function effectively . preferably , the acid should have a molecular weight of less than 250 per available proton . more preferably , this value will be less than 150 , and most preferably less than 75 . an available proton is defined as a hydrogen ion in the molecule which may be donated to free ammonia , so that an acid ammonium salt is formed . the acidity should be high also to limit the amount of acid which must be used for control . one measure of acidity is the pk a , which is the negative of the common logarithm of the acid dissociation constant . a molecule which contains several acidic groups will have several pk a values , one for each of these groups . preferably , the first pk a of the acid should be less than 5 . more preferably , this will be less than 4 , and most preferably less than 3 . the lack of volatility is defined in terms of smell . an acid should be selected which will not annoy or irritate the occupants of these animal areas . any acid which has a noticeable smell should not be used . finally , the lack of toxicity is essential to avoid endangering animal or human health . preferably , the acute oral ld 50 value for the acid should be greater than 500 mg / kg . more preferably , this value will be greater than 1000 mg / kg , most preferably , greater than 2000 mg / kg . many acids will meet the criteria of the instant invention . these include certain naturally occurring and artificial carboxylic and substituted carboxylic acids , as well as phosphoric acid . some particularly useful acids are indicated in table 1 . these all have low volatilities and hence no odors , low toxicities , good acidities , and low molecular weights per available proton . other acids meet some but not all of the criteria , and therefore are not suitable . for example , acetic acid has reasonable acidity , low molecular weight , and low toxicity , but is volatile and thus has a strong and unpleasant smell . boric acid is low in molecular weight , toxicity , and volatility , but is not very acidic . it should be noted that having acidic protons is a crucial point of this invention . thus , salts of acids meeting the above criteria are not generally effective . the sodium salt of citric acid is not a useful ammonia control agent . table 1______________________________________some acids processing desirable attributesfor use in preventing the accumulation of ammonia . molecular first weight / oral ld . sub . 50acid pk . sub . a available proton ( mg / kg ) smell______________________________________citric 3 . 1 64 11 , 700 ( rat ) nonefumaric 3 . 0 58 -- nonemaleic 1 . 8 58 700 ( rat ) faintmalic 3 . 4 67 5 , 000 ( rabbit ) nonemalonic 2 . 8 52 1 , 300 ( rat ) nonephosphoric 2 . 1 33 1 , 500 ( rat ) nonesorbic 4 . 8 112 7 , 400 ( rat ) nonesuccinic 4 . 2 59 -- nonetartaric 3 . 0 75 -- none______________________________________ the conventional animal litter , bedding and absorbent materials used in animal areas includes straw , wood shavings , wood chips , saw dust , clay , rice hulls , corn cobs , sand , vermiculite , etc . mixtures of these materials can also be used . methods of application must ensure a uniform and continuous distribution of the acid . if patches of bedding , litter , or absorbent material exist which are not treated with acid , substantial amounts of ammonia may be formed . one suitable application method is merely to sprinkle or dust compound over the bedding , litter , or absorbent material as a pure solid . compounding with one or more additional solids prior to sprinkling or dusting would be acceptable . these solids might absorb moisture from animal wastes , prevent the formation of some gaseous toxicant other than ammonia from said wastes , be colored to indicate the presence of the compound , or have some other purpose . examples of such solids include zeolites , iron oxide , vermiculite , and other inorganic oxides and similar materials . in addition to being sprinkled or dusted onto bedding , litter , or other absorbent material as a pure solid or in admixture with other solids , the acid may be impregnated onto a solid carrier prior to application . such a carrier may serve merely as a vehicle for the dispersal of the enzyme inhibitor , or it may have some additional function . suitable carriers include natural and synthetic zeolites and clays , as well as other materials . as an alternative to dispersal as a solid , the acid may be dissolved in water or other solvent , and the resulting solution sprayed or poured onto the bedding , litter , or other absorbent material . spraying of a solution is a preferred method of application , as it may yield a very uniform distribution of the compound . a hand - pumped sprayer or other device may be used for this purpose . slurries may be used in place of solutions for solvents in which the compound is sparingly soluble . the acid may be applied to bedding , litter , or other absorbent materials before they are placed in animal areas . this application may take the form of simple physical mixing . alternatively , the acid may be impregnated onto the bedding or other material . this impregnation may be done using a spray , immersion into a bath , or other suitable method , with an optional drying step . if the bedding or other material is artificial , the compound may be added to the raw materials during production . the treated bedding , litter or other absorbent material can be used for larger farm animals such as horses , cows , sheep and pigs ; for domestic animals such as cats and dogs ; and for smaller animals such as mice , rats , guinea pigs , hamsters , gerbils and other small mammals . it is recognized that for birds the primary form of nitrogen waste is uric acid and not urea . however , as the uric acid decomposes , it forms urea which can be hydrolyzed enzymatically to form ammonia . control of the levels of this ammonia can be achieved using the present treated bedding , litter or other absorbent material . accordingly , the bedding , litter or other absorbent material can also be used for fowl and poultry such as chickens , turkeys , ducks , etc . to test the effectiveness of the acid the following procedure has been used . a synthetic urine is made by combining 2 . 3 wt % urea and 1 . 1 wt % sodium chloride . to mimic the presence of bacteria , 200 units of jack bean urease is added to the synthetic urine . jack bean urease is a readily available form of urease which is suitable for use in this context because useases from most natural sources appear to act similarly . see &# 34 ; jack bean urease ( ec 3 . 5 . 1 . 5 ). 8 . on the inhibition of urease by amides and esters of phosphoric acid &# 34 ; by r . k . andrews et al , j . am . chem . soc . 1986 , 108 , 7124 - 7125 . this urine is then poured over a sample of bedding or other absorbent material to which the acid has been applied . the treated sample is covered so that any gases produced may accumulate . the presence of ammonia is tested for by using draeger tubes . having described the basic aspect of the invention , the following examples are given to illustrate the specific embodiments thereof . this example illustrates the use of citric acid in the presence of two different types of bedding material . two 8 oz . polyethylene bottles were charged with 15 g of rice hulls and 15 g of sawdust , respectively . into each was added 15 g of the synthetic urine described above , which is a 2 . 3 wt % urea / 1 . 1 wt % nacl solution with 200 units of the enzyme urease . also present in this mixture was 12 mg of citric acid . the bottles were capped , and incubated in a shaker bath at 37 . 5 ° c . after 4 hr , no ammonia smell could be detected in either bottle . by contrast , identical bottles not containing citric acid smelled strongly of ammonia . this example illustrates the use of other acids to control the accumulation of ammonia . following the procedure of example 1 , 12 mg of malic acid , 6 mg of fumaric acid , and 6 mg of phosphoric acid were found to be sufficient to prevent the accumulation of noticeable amounts of ammonia . this example illustrates that acids which do not meet the stated criteria may not be effective . following the procedure of example 1 , boric acid ( 36 mg ) was tested and found to not control the accumulation of ammonia . boric acid has a first pk a of 9 . 1 , and this does not have a first pk a which is within the stated preferred range . this example illustrates that the salts of acids , which lack acidic protons , may not be effective . following the procedure of example 1 , sodium citrate ( 24 mg ) was found not to control the accumulation of ammonia . this example illustrates the effectiveness of citric acid when live urease - producing bacteria were substituted for urease . an 8 oz . polyethylene bottle was charged with 6 g of rice hulls and 24 g of synthetic urine , which is a 2 . 3 wt % urea / 1 . 1 wt % nacl solution to which 24 mg of citric acid had been added . bacillus pasteurii then was added to this mixture , which subsequently was incubated in a shaker bath at 37 . 5 ° c . after one day , no ammonia was evident in this bottle ( less than 5 ppm as measured using a draeger tube ). by contrast , the dead space in an identical bottle not containing citric acid contained more than 700 ppm of ammonia . it is understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of this invention .
the accumulation of gaseous ammonia in areas wherein animals are housed or maintained is controlled by providing to the areas animal litter , bedding , or other absorbent material which contain a low molecular weight , non - volatile organic acid . acids such as citric , malic , fumaric , phosphoric , tartaric , maleic , malonic , succinic , sorbic and mixtures of these acids are used and especially phosphoric and fumaric . these acids can be used in concentrations of about 0 . 0001 to 2 wt % of the dry bedding .