April 1951 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 871

Further evidence is the fact that in soft rvater runs (where calcium precipitates could not form) the addition of alkalies had no deleterious effect on the protective action of the synthetics.

The mechanism of filming by inorganic precipitates alone, in the absence of foodst)uffs, is also of interest. Figure 1 shows that sodium metasilicate (SlIS j and trisodium phosphate (TSP) film strongly above 0.2% in hard water. The ~ v a y in which these films form in the dishwashing cycle is as follows: When the alkali is added to the hard water, it precipitates all of the calcium and magnesium and leaves an excessof unprecipitated alkali in jolution. At the end of the wash cycle this alkaline water is left clinging to the tableware, and the incoming hard rinse water then forms additional precipitate in situ as i t strikes the glass surface (5 ) . This is confirmed by the fact that little film is formed if the rinse is carried out with soft water (so that secondary precipitation cannot occur). The inorganic precipit,ates so formed apparently adhere to the glass surface through electrical forces of the kind that von Buzagh ( 1 ) found operative in causing quartz. or calcite pow-ders to cling to quartz plates under water. As Figures 2 and 3 show, the addition of certain synthetic detergents (especially Ant,aros A and Ultrawet K ) apparently enhances the adhesion of the* inorganic precipitates, contrary t o their action on food soils where the synthetics prevent adhesion. Although the explanation for this effect is not yet apparent, it can be avoided by the use of special synthetics such as Antaron L520, combined with low-filming alkalies such as pyrophosphates.

A secondary way in which the synthetic detergents reduce filming is by increasing the rate of drainage. The ware in the machine is covered by a layer of soiled wash water a t the end of the washing cycle (before the rinse). It has been found that the presence of the synthetics enables more of this dishwater t o drain away before the rinse starts; this leaves less redepositable ma- terial clinging to the glassware and dishes, and also results in cleaner rinse water during the final operation. Because the food particles and inorganic precipitates left in the clinging wash water a t the start of the rinse are all protected by the adsorbed hydro- philic molecules of the Eynthetic, no difficulty is experienced in washing them an-ay and leaving film-free surfaces.

CONCLUSlONS

Under the particular test conditions used here, mechanical dishwashing compounds based on low-foaming anionic organic detergents appear t o offer certain advantages over the conven- tional polyphosphate-alkali mixtures.

Using a synthetic of this type, together with properly selected builders, redeposition of inorganic precipitates and foodstuffa is held to a minimum, and the result is brighter glassware and freedom from film formation. I n addition, the wetting action of the synthetic enables the water t o drain and spread more effec- tively with greater freedom from salt rings and water spot,s as a result.

ACKNOW-LEDGMENT

The authors wish to thank AIarvin Kopp of this laboratory for aid in statistical analysis and T. E. Graham of hntara Producta for help in arranging field performance surveys.

LITERATURE CITED

(1) Buaagh, A. yon, J . Phys . Chem., 43, 1003 (1939). ( 2 ) Gilcrease, F. W., and O’Brien, J. E., Am. J . Pub. Health, 31, 143

(3) Hughes R. C.. and Bernstein, R., IND. ESG. CHEM., 37, 170

(4) Machlis, S., and Michaels, E. B , Soap Sa7tit. Chemicals, 24, 42

(5) hiann, E. H., and Ruchhoft, C. C . . 6’. S . Pub. Henlili Repts., 61,

(1941).

(1 945).

(1948).

539 (1946). \ - - - - , . (6) I b i d . l p . 877. ( 7 ) Siven, W. JV., “Fundamentals of Detergency,” p. 200, Kew

York, Reinhold Publishing Corp., 1950. ~~

(8) Ibid.. p. 224. (9) Lange. S. A . , “Handbook of Chemistry,” 4th ed., p. 578,

Sandusky, Ohio, Handbook Publishers, 1941. (10) Xorrie, F. I., and Ruchhoft, C. C., Division of Water, Sewage,

and Sanitation Chemistry, 116th Meeting, AM. CHEM. SOC., Atlantic City, N. J., 1949.

(11) Pon-ney, J., and Noad, R. W., J . Teztile Inst., 30, TI57 (1939). (12) Schwartz. C.. and Gilmore, B. H., IND. ESG. CHEX, 26, 998

(13) Walter, TI-. G., Am. J . Pub. Health, 38, 246 (1948). (14) Wilson, J. L., and hlendenhall, E. E., ISD. Esc. CHEST., ANAL.

RECEIVED .4pril 12, 1950. Presented before the Division of Colloid Cbem- is t ry a t the 117th Meeting of t he A h i E R I c . a N CHESICAL SOCIETY, Houston, Tex.

(1934).

ED., 16, 253 (1944).

Preparation and Properties of Urea-Form

K. G. CLARK, J. Y. I-EE, K. S. LOVE, AXD T. A. BOYD Bureau of Plant Industry , Soils, and Agricultural Enginebring, United States Department of Agriculture, Beltsville, M d .

S AS earlier communication Clark, Yee, and Love ( 3 ) de- I scribed both dilute and concentrated solution procedures for carrying out the reactions between urea and formaldehyde to form products (urea-form) of low solubility suitable for fertilizer use, The products of the two procedures differ from each other in their content of unreacted urea and in the relative proportions of the various urea-formaldehyde complexes present. The dilute solution products which are separated from the mother liquor and washed, necessarily contain less unreacted urea, and a lower proportion of their urea-formaldehyde nitrogen in readily soluble form than the concentrated solution products which are neither separated from the mother liquor nor washed Both types of products, however, are much less soluble than the usual chemical nitrogen materials now used for fertilizer purposes

Yee and Love ( 1 1 ) demonstrated for products of the dilute

solution type that the rate of conversion of their nitrogen to nitrate form in soil media, a generally accepted measure of the rate a t which nitrogen becomes available to plants, was deter- mined largely by the mole ratio of urea combined with formalde- hyde in the product. Because the nitrogen content of the solu- tions obtained in determining the solubility of the products in water increased continuously with time, an empirical solubility determination was devised for comparing the relative solubility of the materials. The empirical solubility data were found to be in general agreement with the mole ratio of urea to formaldehyde, U/F, and the nitrification behavior. Fuller and Clark ( 5 ) re- ported data which indicated that enzymatic hydrolysis largely was responsible for conversion of the nitrogen to readily nitrifiable form.

872 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 43, No. 4

T h e present work was undertaken further to define the conditions under which urea and formaldehyde react to form complexes of low solubility suitable for use as slowly available sources of nitrogen for crop growth, to devise laboratory procedures for more rapid evaluation of the probable fertilizer value of such products than the cus- tomary nitrification and vegetative growth experiments, and to examine means for determining the relative pro- portions and solubilities of the various components con- stituting the over-all reaction product.

The reaction between urea and formaldehyde leading to the formation of urea-form appears to progress through methylol urea formation to increasingly more complex polymethl-lene urea compounds. Neutralization of the

reaction mixture at the proper stage largely inhibits com- pletion of the reaction to excessively insoluble materials and stabilizes the product to subsequent heat treatment. Correlations were found between empirical solubility measurenien ts and nitrificaLion characteristics which permit rapid laboratory evaluation of the suitability of urea-form materials for fertilizer use. Application of solu- tion analysis procedures provides a means for determining the relative proportions and solubilities of the components of urea-form materials.

Progress has been made in defining the conditions for the preparation of urea-formaldehyde reaction products suitable for fertilizer use and in developing rapid methods for their evaluation.

. i Concentrated solut ion p r o d u c t s

x r = i O . E I * * 0 6 5 + 0 . 4 y i". 4 -

- h O i l u l e s o l u t i o n products

0.98" 0.788~ I

I I 0 10 20 30

N i t r i f i c o t t o n . 3 w e e k s - Percent

Figure 1. Relation between Primary Nitrogen Solubility and Degree of Nitrification

3 weeks at 30° C.

SOLUBILITY PATTERN, A / B z

Originally, a single empirical solubility procedure was used to measure the total nitrogen dissolved by digestion of a 1-gram sample in 400 ml. of water a t 30" C. for 24 hours. Tlie value found was corrected for the unreacted urea content of the sample and the solubility of the urea-formaldehyde nitrogen a t first es- pressed as milligrams of nit,rogen per 100 ml. of solution a d later as parts per million under the designation "solubility in- des" (3). I n order to improve the over-all characterization of the solubilit,y relationships and the nitrification behavior of the product, the initial solubilit,y determination has been supple- mented more recently by a second empirical procedure and the results of both determinations are espressed as a solubility pattern, A / E z , Determined under the above conditions t,he primary solu- bility value, A , of this pattern now includes the nitrogen prcsent as unreacted urea and is expressed as the percentage of the total nitrogen in the sample. The secondary solubility value, E,, relates to the percentage of the total nitrogen dissolved when the

TABLE I. EFFECT OF DIGESTION PERIOD o s SOLUBILITY PATTERN, A / B ,

Duration of Primarv and Secondary Digestion Peribds, Hours

24/24 16/24 16/20 Sample U/F Mole Moisture,

No. Rat io 70 Solubility Pat tern, A / B z , 70 4910B 1.35 4 .34 49.0/11.3 48.8/11.7 49.1/11.4 481) 1.36 2.46 42 .9 /9 .7 4 3 . 1 / 9 . 6 4 3 . 1 / 9 . 6 4980 1.35 2 .38 38.5/7.3 38.6/7.3 38.3/7.0

undissolved residue from the primary solubility determination is digested with 2000 ml. of water at 30" C. for 24 hours.

As shoi\n in Figure 1, the concentrated solution products ex- hibit considerably higher primary nitrogen solubility values than the dilute solution products for equal degrees of nitrification in a 3-week incubation period. The differences between the A solubility values and the initial nitrification behaviors for the two types of products presumably are related to the greater tendency for the less complex urea-formaldehyde materials in the concentrated solution products t o undergo further reaction during the incubation period. For each type of product the correlation between the primary nitrogen solubility and the nitrification in 3 weeks was significant a t odds of better than 99 to 1. Figure 2 shows that the secondary solubility, E,, also is significantly correlated with the increase in nitrification between 3- and 15- week incubation periods a t odds of better than 99 to 1 for both preparation procedures. I n consequence, similar availability patterns may be evpected from the two types of materials when their B , values are nearly the 8ame and the A value of the con- centrated solution product is approximately twice that of the dilute solution product.

TABLE 11. EFFECT OF M A X I M ~ I REACTION TEUPERATURE ON CHARACTER OF COXESTRATED SOLUTION PRODUCT

hlaximum Unreacted Solubility Reaction or iilois- h-itrogen Urea U/F Pat tern,

Sample Pouring ture, Content, Content, Mole A / B z , h-0. Temp., C. 70 % 7G Ratio yo 281 35 2 . 7 2 39.60 9 . 2 2 1 . 4 0 47.2/11.4 274 50 2 . 2 4 3 9 . 9 2 8 .40 1 .41 49.4/10.9 282 G O 2 .83 39 .60 10.00 1.38 4 1 . 3 / 9 . 1 283 96" 2 . 9 8 39 .55 12 .34 1 . 3 4 36.1/5.0 a Sample not poured; reaction continued t o solidification in reaction vessel.

' The primary and secondary digestion periods used in the empirical solubility procedure may be reduced by 8 and 4 hours, respectively, as s h o m in Table I, without appreciably affecting the values obtained. Further reduction in the digestion periods, however, failed either t o yield comparable results or to decrease the over-all time required. With the exception of the data in Table I, all solubility pattern data presented in the present paper are based on 24hour estraction periods for both A and B,.

FACTORS AFFECTING CHARACTER OF COSCEKTKATED SOLUTION PRODUCTS

Clark, Tee, and Love (3) showed that the mole ratio of urea to formnldohydc, nitrogen content, unreacted urea content, and primary nitrogen solubility of urea-form products increased 89 the initial mole ratio of the reactants was increased when the maximum temperatures of the reaction between crystalline urea and acidic 37 yo formaldehyde solutions were limited to about 55" to 60" C.

April 1951 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 873

TABLE 111. EFFECT O F RAPID NEUTRALIZATION .4SD SUBSE- QUENT HEAT TREATVENT ON CHARACTER O F COSCENTRATED

(Init ial U/F mole ratio, 1 33, reacted a t pH 8 and 40-4.3' C. for 42 minutes before acidulation to p H 3 7)

Si t rogen Unreacted C/F Solubility Sample hloistrire, Content, Urea Mole Pa t te rn ,

h-0. 70 % Content, % Ratio A / B z , 70

SOLUTION PRODUCT

357Da 2 . 3 9 35 .24 4 . 3 5 1 . 3 4 33.4, /10.6 357ADb 1 . 5 9 38 .84 7 . 3 1 1 . 2 9 6 3 . 7 / 1 9 . 0 357AH80c 1.86 38 .93 6 . 9 5 1 26 61 9119.1 357II80d 2 . 4 7 3 9 , 2 0 5 . 9 8 1 29 2 7 . 0 / 8 . 8

a Air dried a t room temperature. b Xeutralired with gaseous ammonia and then air-dried. e Xeutralized with gaseous ammonia and heated in air oven a t 80' C.

for 2 hours. d Heated in air oven a t 80' C. for 2 hours.

-1

A r . 0.92" a 6 7 5 C 2 . 7 4 ~

m'

2 I O

0 5

0 I I I O 20 30 40 50 60 0

Nitr i f icat ian, 15 weeks - 3 weeks, Percent

Figure 2. Relation between Secondary Kitro- gen Solubility and Degree of Nitrification in 15

Weeks RIinus That in 3 W'eelrs at 30" C.

The data in Table I1 are typical of the changes observed in the urea-formaldehyde mole ratio, unreacted urea content, and nitrogen solubility when the reaction mixture Icith an initial mole ratio of reactants of 1.5 and p H of 3.7 is quickly chilled on reaching the indicated maximum temperature by pouring a thin layer into a n aluminum pan a t room temperature. The un- reacted urea content passed through a minimum value, the mole ratio of the urea-formaldehyde compounds formed tended to re- main constant or to increase and then decrease, and the solu- bility pattern progressively decreased as the maximum reaction temperature was allowed to increase. The sccondary solubility, however, suffered a proportionately greater decrease than the primary solubility.

Data typical of the effect of rapid neutralization and subse- quent heat treatment on the character of the final product are given in Table 111. I n this case, the reaction mixture with an initial urea-formaldehyde mole ratio of 1.33 was maintained a t pH 8 and 40" t o 43" C. for 45 minutes, cooled to 30" C.. and acidified to p H 3.7 rrith sulfuric acid. The temperature increased spontaneously to 50" C. in approximately 1.5 minutes, a t which point the reaction mixture was poured into an aluminum pan a t room temperature to a depth of approuimately 0.75 inch and allowed to solidify. The freshly solidified cake was broken up and subjected to four different treatments, as indicated in Table 111.

From the data it is apparent that neutralization of the free acid content of the moist freshly prepared cake effectively stopped the reaction short of completion to produce a much more soluble product with a lower urea-formaldehyde mole ratio and higher unreacted urea content. I icat treatment of the inoist neutralized cake resulted in only minor changes in solubility, mole ratio, and unreacted urea content. Heat treatment of the unneutralized moist freshly prepared cake, hoviever, increased the unreacted urea content and decreased both the primary

and secondary solubility values. Heat treatment of moistened and slightly acidified dilute solution products also has been observed to increase the free urea content and to decrease the urea-formaldehyde mole ratio and solubility values.

These observations, together Tvith the data of Table I1 and the earlier findings (3) that under acidic conditions in the presence of an eucess of urea, unreacted formaldehyde disappears from the reaction mixture prior to completion of the over-all reaction, indicate that the over-all reaction tends to proceed through the formation of methylol urea and the generaiized series of reactions indicated in Figure 3. The methylol urea reacts with urea to form methylene diurea and water. Depending on the initial mole ratio of urea to formaldehyde, the methylene diurea formed may react successively with additional methylol urea to form higher polymethylene ureas with the liberation of one mole of water for each mole of niethylol urea coniumed. Interaction of the various methylene ureas to form still higher polymethylene products with the liberation of urca mould account for the increase in free urea content observed when unneutralized prod- ucts are subjected to heat treatment. Presumably the inter- action between the methylene ureas is initiated before complete disappearance of the methylol urea, so tha t during the early stages of the reaction the urea-formaldehyde mole ratio tends to increase and the unreacted urea content to decrease. During the later stages the mole ratio decreases from the maximum value attained and the unreacted urea content increases above the minimum value. T h e solubility of the product decreases con- tinuously, hovever, as more complex and higher molecular m-eight compounds are being formed as the result of both re- actions.

Yeutralization of the reaction mixture may be employed effectively to stop the reactions a t a desired stage. Subsequent drying operations then may be carried out a t suitably elevated temperatures without appreciable change in the solubility and availability characteristics of the product.

Figure 4 shows the time-temperature relationships resulting when external heating of urea-formaldehyde solutions which had been maintained under alkaline conditions (pH 8.0 and 40" to 42' C. for 45 minutes) favorahle to conversion of an appreciable portion of the formaldehyde to monomethylol urea (4, 10) was

i I

I Lnreacted u r e o I I I

I

-- -. ~~

- n -

Figure 3. Generalized Reactions and Trend in Urea- Formaldehyde Rlole Ratio, Unreacted Urea Content, and Solubility of Products as Reactions Progress

a74 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 43, No. 4

TABLE Iv. EFFECT OF DELbYED A~DJUSTYENT O F UREA- FORXALDEHYDE MOLE RATIO ON CHARACTER OF PRODUCT

Prnrlnot

Un- Solubility U/F Mole Rat io hlois- U/F Total reacted Pat tern,

Sample of Reactants ture, mole nitrogen, urea, A / B z , KO. Initial Final '% ra t io % % % 273 1 . 2 5 1 . 2 5 3 . 2 1 1 . 2 6 38 .66 3 . 2 4 10.9/3.0 300 1 . 5 0 1 . 2 5 4 . 9 3 1 . 2 7 37 .91 4 . 0 7 1 1 . 2 / 3 . 6 276 1 . 5 0 1.50 2 . 2 3 l . A l 39 .87 8 . 4 9 4 7 . 3 / 1 0 . 5

1 A c p H 4.5

50w'/ I I 1 I I I 2 3 4 5 6 7 8

Time - Minutes

Figure 4. Time-Temperature Relationships after Acidulation

Mixtures produced by dissolving crtstall ine urea in 379% for- maldehyde a n d mainta ining resulting solution a t 40-42' C.

and pH 8 for 45 m i n u t e s

discontinued and the solutions were acidulated with sulfuric acid to different pH values. I n each case, decrease in p H increased the rate of reaction as measured by the spontaneous increase in temperature, and the rate x-as still further increased as the reactions involving the formation of the less soluble and more complex compounds became the controlling factor. iilthough the difference between the rates was more pronounced a t the higher pH values, the reactions proceeded more rapidly a t the lower values.

The data in Table 11- indicate that the relative proportions of monomethylol urea, urea, and formaldehyde in reaction mixtures prior to acidification have little effect on the character of the final product. I n these experiments the reaction mixtures were maintained under alkaline conditions as before and acidulated to pH 3.7 to promote formation of polymethylene ureas, and the reaction mixtures were chilled by pouring into a pan when the temperature reached 50' C.

The urea-formaldehyde ratio of the nlixture TYas not changed when the acid was added, but in one case ( S o . 300) sufficient formaldehyde solution Fas added after initiation of the pre- cipitation reaction to reduce the urea-formaldehyde mole ratio from 1.50 to 1.25. .Is shown, t,he solubility characteristics of the products were independent of any reaction rvhich occurred prior to f ind adjustment of the urea-formaldehyde ratio.

SOLUBILITY ANALYSIS OF PRODLCTS

h number of investigators (6-8) have described the possibili- ties and limitations of solubility studies for determining the purity of a material, and for determining the number of components, their individual solubilities, and the relative amounts of each present in a mixture. As indicated by Figure 5 , which illus- trates a hypothetical case for a mixture containing three nitrogen compounds, the solubility analysis is based on the linear rela- tionship which exists between the portion of the solute dissolved

and the composition of the system over a range of solvent to eolute ratios for which there is no change in the number of solid phase components. When the number of solid phases present is reduced by one, corresponding to complete solution of one of the original components, the slope of the curve changes abruptly to a new linear relationship. Thus, the number of segments equals the number of components. Extrapolation of the segments t o the y-axis permits determination of the nitrogen solubilities of each component and the percentages 0 1 the tot,al nitrogen present in each form in accordance with the formulas shown in the figure.

Figure cj shows the solubility analysis curves obtained for typical concentrated and dilute solution products. As is ap- parent, location and determination of the number of segments for water t o sample ratios below about 0.4 is particularly difficult and subject t o large uncertainties. In addition, the known content of unreacted urea and its solubility ( 9 ) must be taken into account. Table T' summarizes the results of these solubility analyses. T h e concentrated solution product, CY-22, contains about 11% of its nitrogen as unreacted urea and more than 27% as urea-formaldehyde products with solubilit'ies equivalent t o 2.7 t o 2.8 grama of urea per liter. I t also contains approximately 45y0 its nitrogen in forms having solubilities equivalent t o 4 t o 8 mg. of urea per liter. I n contrast, the dilute solution product, G-5, contains relatively little unreacted urea and of the more soluble forms of urea-formaldehyde complexes, but has nearly

TABLE I-, COMPARISON O F SOT,UBIIJTY O F COWCEXTRATED AND DILUTE S O L ~ T I O N PRODUCTS

Concentrated Dilute

481 or CY-22 Solution Product , Solution Product,

476 or G-5 I t em U / F niole ratio Total nitrogen, To Urea nitrogen, To hloistilre, "F Solubility pattern. -4 I B z , yo

Solubility, Urea Equivalent, lfg. 'L.

-l-R _ _ 14-18 30-33 45-50 80-90

170-180 200-225

1100-1150 2700-2800

1310 X loaa 0 Urea solubility a t 30' C.

1 . 3 3 1 . 3 1 3 8 . 0 3 8 . 5

4 . 3 0 . 9 4 31 3 . 6 6

49 . o ' 11 .2 14.3 , '18 .7

9 Total Si t rogen

4 5 . 2 5 . 2 3 , 4 . .

i : 9 2 . 4

27:6 1 1 . 3

79:4

l b : 2 3 6 1 . 6

2 . 7 . .

i:4

Composition of the system, L H , o / g N

Figure 5 . Graphical RIethod for Evaluating Xumber of Components, Solubilities, and Relative Amounts Present in Rlixture from Solubility Determinations

April 1951 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

_.I 4

G- 5 CY-22 Dilute solution Concentrated solution

product product

U/F 1.31 1.35 A/B,, % 14.3 / 18.7 49.0/ 11.2 Total N, % 38.5 38.0 1 Urea N, % 0.9 4.3

Composition of the system, LHz0 / g sample

Figure 6. Application of Solubility Analysis Procedure to Urea-Forms CY-22 and G-5

80% of its nitrogen in the solubility range equivnlent to 14 to 18 mg. of urea per liter.

PLANT GROWTH T E S T S

Greenhouse studies (1 , 8 ) with grasses have shown that the nitrogen in urea-form materials becomes available to the crop more slowly and more uniformly throughout the gron-ing season than that of conventional nitrogen fertilizers. This difference between the nitrogen availability patterns of the two types of materials for equivalent applications of nitrogen resulted in a lower initial response to urea-form than to st’andard nitrogen sources, and in a relatively greater response t o urea-form during the later stages of growth. T h e over-all upt,ake of nitrogen from properly prepared urea-form materials equaled or exceeded that from materials which exhibited greater initial availabilit’ies. Single applicat,ions of urea-form were made a t rates as high as 800 pounds of nitrogen per acre (equivalent to nearly 2 tons of ammonium sulfate) without any evidence of burning or other detrimental effect. A single application of urea a t one half this rate or 400 pounds of nitrogen per acre, hoLvever, killed all the plants. T h e uptake of nitrogen when urea-form vias applied a t levels between 200 and 800 pounds of nitrogen per acre was approximately in proportion to the amount of nitrogen added.

Results, as yet unpublished, have been obtained in field experiments a t Beltsville, l l d . , llarysville, Ohio, and Tifton, Ga., clearly indicating the late-season superiority of urea-form materials for turf . With few exceptions, however, field esperi- ments on row crops and small grains in rt-hich urea-form has been used as the sole source of fertilizer nitrogen a t normal levels of application have not short-n satisfactory results as measured by crop yield increases. Whether supplying part of the nitrogen as urea-form and pari as a more rapidly available form would more nearly meet crop requirements reniains to be determined. I n the case of tohacccj in Connecticut, sach a partial replacement of a portion of the customary nitrogen application has resulted in increased J-ield and quality of the crop.

Vegetative esperiments have

87 s SUMMARY

Correlations have been found between empirical solubility relationships of urea-formalde- hyde reaction products and their nitrification characteris- tics which permit laboratory evaluation of the snitahility of such products for fertilizer use. The reaction hetween urea arid formaldehyde leading to fornxi- tion of urea-form appears to progress through iiiethylol urea formation to increasingly more complex polymethylene urea compounds. Neutralization of the reaction misture a t the proper stage largely inhibits completion of the reaction to excessively insoluble materials and stabilizes the product t,o s u b s e q u e n t heat treatment. Application of the procedures of solubility analysis to a tii- lute and a concentrated solu- tion product indicated that the solubility of the major portion of the nitrogen was in the range equivalent to 4 t o 18 rng. of urea per liter.

shown that properly prepared urea-form materials are superior as the sole source of fertilizer nitrogen for turf t o more soluble and more rapidly available nitrogen fertilizers. Experiments also have given some indication that the use of urea-form to supply a portion of the fertilizer nitrogen may improve both the yield and quality of row crops.

LITERATURE ClTED

.kniiger, J\-, H., Clark, K. G., Lundstrom, F. O., and Blair,

rlrmiger, W. H., Forbes, I., Jr., Wagner, R. E., and Lundstrom,

Clark, K. G., S e e , J. Y., and Love, K. S., ISD. ENG. CHEIr ,

Crone, G .I., Jr., and Lynch, C. C., J . A m . Chem. SOC., 70,

Fuller, IT. H., and Claik I<. G., Proc. Sotl Science SOC. Am., 12,

A. E., A g r o n . J . , 43, 123-7 (1951).

F. O., I h d . , 40, 342-56 (1948).

40, 1178-83 (1948).

3795-7 (1948).

198-202 (1947). Herriott, R. SI.. Chem. Rea., 30, 413-21 (1942). Kunitz. SI.. and Sorthrup, J. H., Curnp. rrrad. trau. lab. Curls-

berg, 22, 288 (1938). Northrup, J. H., and Kunitz, ll., J . Gen. Physiol. , 25, 465

Pinck, L. A,, and Kelly, AT. .4., J . A m . Chem. SOC., 47, 2170

Smythe, L. E., J . Phys. Colloid Chem., 51, 3R9 (1947). Tee, J. T., and Love, K. S., Proc. S o i l Sci. SOC. Am., 11, 3 8 9 ~ 4 2

(1941).

(1 925).

(1946)

RECEIVED 3Iay 2 , 1950. Presented before the Division of Fertilizer Cheni- istry at the 116th Meeting of the BJIERICAS CHE\IIC.AL SOCIETY, Atlant ic Ci ty , S. J.

Heat Transfer-Correction In the review paper on “Heat Transfer” [IND. ENG. CHEY.,

43, 99 (1951)] references (14) , (69)) and (73) are to the Trans- actions of the Institution of Chemical Engineers, and not to the Transactions of the American Institute of Chemical Engineers, as erroneously listed on pages 101 and 102.

GEORGE T. SKAPERDAS