X 1812 Davy, studying the action of car- bonyl chloride on ammonia (##),. 6rst @ I synthesized and described but did not

recognize urea, a salt perfectly neutral and dry, but deli- quescent by attracting moisture from tlie air. It is remarkable that on the formation of this ammoniacalsalt, gas (phosgene) combines with as much as four times its bulk of ammoniacal gas. The reaction so accurately observed was:

COCll + 4N& = CO(NIIA + ~NHICI Thus it was left for Wohler (88) to announce the synthesis of urea, making memorable the year 1828 and destroying the existing sharp demarcation between organic and inorganic matter. Seventeen years elapsed before the next synthesis of an organic compound-acetic acid by Kolbe. That tlie Wijhler synthesis could be reversed and urea converted back to ammonium cyanate was not established until 1895 (79).

In 1773 Rouelle (64) had obtained a saponaceous extract of urine by alcoholic extraction of evaporated urine. Twenty- six years later Fourcroy and Vaquelin ( S I ) obtained urea in a comparatively pure state from the same source and, recog- nizing it as a new compound, gave it the name ureo. Twenty years later Prout (62) devised a method for obtaining pure urea from urine and published the first analysis of this compound. In 1829 large quant.ities of urea were required in the Hospital of St. Aiitoine in Paris for conducting experi- ments (which were unsuccessful) on diabetics, and Henv ($8) developed a method for preparing it in quantity from fresh urine through the use of lead salts for the removal of acids and mucous substances.

Development Process As mentioned, urea was first synthesised from ammonia

and phosgene by navy in 1812, though ltegnault (1838) is usually given credit (69) for being the first to prepare urea by this reaction. Well over 6fty different methods have since been devised for the synthesis of urea. It is of interest, how- ever, that only two methods have attracted industrial atten- tion, the hydrolysis of cyanamide and the interaction of carbon dioxide and ammonia.

During the World War as an emergency measure, small quantities of urea were manufactured in Canada and by the du Porit Company from calcium cyanamide. A pilot plant for the production of urea by the Lidholm process for the hydrolysis of calcium cyanamide was operated in 1925 at, Niagara Falls (65).

Until 1935 the worlds production of solid synthetic urea

ABSORBXMS IX C ~ ~ f i - l ~ i i . 1 . m ~ P~. . \XT

solid urea, and in IYoveinhr, 1935, the first commercial pro- duction of synthetic solid urea begm in the United States.

All commercial synt,hetic urea now producod in Germany, England, and the United States is obtained thmngh the reac- tion of ammonia and carbon dioxide.

In 1868 Basaroff (9) first suggested the synthesis of urea from carbon dioxide and atnmonia, showing that both am- monium carbamate and enrbonatc when heated in a sealed glass tube yield urea. Bourgeois ( I I ) further fitudicd this reaction to improw the yield but met with little success,

WBS largely controlled by Germany. E a r l y in 1935 t h e Imperial Chemical Industries, Ltd., Billingham, Eng- land, commenced the production of synthetic urea 0x1 a relatively small scale. In 1932 E . I. d u P a n t d e Nemours & Company, Inc., developed urea- ammonia liquor, essen- t i a l ly a so lu t ion of crude urea in ammonia for use in the amnio- niation of superphos- phatefertiliser ( I S , GO) This mas followed by s tud ie s on the high- pressure syntliesis of

CRYSTAL UREA

Industrial Development and Properties

J. F. T. BERLINER E. I. du Pont de Nernoum & Company, Inc.,

Wilmington, Del.

obtaining yields from 1 . 5 t o 9 . 5 2 per cen t urea. l i e noted t h e strong corrosive action of the carbon dioxide- ammonia system on iron. In 1882 Mixter (59) shon.ed that urea could, he formed by passing dry carbon di- oxide and ammonia througli a heated tube. In 189i Slosse (72) oh- tained urea by passage of a silent electric dis- charge through a dry gaseous mixt.ure of one volume of carbon diox- ide and two volumes of ammonia. Although the transformation of

518 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 28, NO. 5

TABLE I. PHYSICAL PROPERTIES OF UREA Mol. weight Melting point (decomposes) C. Melting point at 3000 atm.," C. Triple point transformation. C. at 6635 at,m.

w a s , 1 to 2 Tri le point volume change, kg./cc. I

Crystal habit Refractive indices at 20 C. Heat of fusion, cal./gram Heat of combustion (solid), cal./gram Heat of solution in water cal./gram Heat of solution in metdanol, cal./-

Heat of solution in ethanol, cal./- gram

gram

60.047 132.7 (68) 150 (18)

102.3 (18)

48.0 (18) 0.6 (18) 1.335 0.000208

($4) :

Tetragonal-scalendohedral (37) Optical sign, positive; axial r

A/geedles or rhombic prisms 1.484 and 1.602

= 1:0.833 (57)

57.8 (58) 2,531 (46) -57.8 (58)

-46.6 (75)

-50 2 (76)

Free energy of formation at 25' C., cal./mole:

Thermal conductivity of crystals,

Axial thermal conductivity ( A - B ) Specific heat (20 C.) , cal./gram/' C. Dissociation constant, 2"" c. Dielectric constant (22 (3.1, c . g. 8 .

units at 4 X 106 cycles/sec.

Solid -47,120 ( 4 3 ) Aqueous -48,720 ( 4 3 ) cal./sec./sq. cm./O C./cm. 0.191

A / C = 0.79 (48) 0.320 ( 4 1 )

1.5 X 10-4 (80)

3.5 f 0.2 ( 4 1 A , 7 4 )

,atio

ammonium carbamate to urea had been known for some time, the first markedly successful work was undertaken by Fichter and Becker (29) in 1911. They placed carbamate in steel bombs and studied the effects of time, temperature, and pack- ing density on the conversion, concluding that 135" C. was the optimum temperature and 42 per cent the maximum conversion attainable a t this temperature. This same year Lewis and Burrows (50) published their studies on the free energy of urea and the synthesis of urea from carbon dioxide and ammonia, which tended to confirm the results of Fichter and Becker.

During the war when the problem of nitrogen fixation be- came acute in France, Matignon and Frejacques (0'7) under- took the study of urea synthesis and showed that, although the temperature exercised no profound influence on the equilibrium, the speed of the conversion is very much affected. The addition of dehydration catalysts accelerated the rate of conversion a t the low temperature, but they contributed no appreciable improvement above 150" C.

In 1919 the Fixed Nitrogen Research Laboratory began an investigation of the synthesis of urea from ammonia and carbon dioxide and in 1922 developed a process which was operated on an experimental plant scale (46). This consisted of charging briquetted ammonium carbamate into an auto- clave maintained at 150" C. and passing the liquid product into a still where the unconverted ammonia and carbon dioxide were recovered and recycled. These studies suggested that higher temperatures would result in higher yields, agree- ing with the work of Matignon and Frejacques, Krase and Gaddy further showed that the use of an excess of ammonia over that combined as carbamate materially increased the conversion to urea. Carbon dioxide did not show this effect (47). The maximum conversion of ammonium carbamate to urea, which in the absence of excess of ammonia was about 44 per cent, could be increased to 85 per cent by the use of about 300 per cent excess ammonia. The slope of the con- version curve indicated that further excess of ammonia would have little effect on the conversion. The effects of tempera- ture, materials of construction, and a number of other factors were studied by this group (i7, 18, 19, 49). In 1930 a con- tinuous process for the synthesis of urea from liquid ammonia and carbon dioxide was described. A small unit producing 175 pounds (386 kg.) of urea per day was operated a t 35 to 37 per cent conversion a t 153" C. (48).

While ammonia, carbon dioxide, and water are by them- selves practically noncorrosive to steel, when combined they are astonishingly corrosive. Under urea synthesis conditions the mixture will dissolve iron filings rapidly, and ordinary steel plate will dissolve a t the rate of about 130 grams per square meter per hour, or more than 10 ounces per square foot per day (77). Chrome irons and a number of ordinarily resistant alloys are also rapidly attacked. Lead is attacked a t about one-thirteenth the rate of steel.

The primary difference in the manufacture of urea in the United States and in other countries is in the treabment of the unconverted ammonia and carbon dioxide. Both in England and in Germany gypsum conversion plants have been operated in conjunction with the urea synthesis operation. However, in Germany, the present practice is to recycle the uncon- verted gases a t sufficiently high temperature to prevent formation of solid compounds. In this country where there are large amounts of ammonium sulfate available from coke- oven operations, its further production is unattractive. The utilization and handling of the unconverted gases has con- stituted one of the major problems in the domestic produc- tion of urea.

The world's present synthetic urea production capacity is about 190 tons a day. Prior to 1936, with the exception of the small amount produced during the World War, all domes- tic urea requirements were derived from Germany. There is now sufficient production capacity in the United States

TABLE 11. SOLUBILITY OF UREA IN VARIOUS SOLVENTS Solubility in Water (44 , 61, 70, 81)

Temp., O C. 100 G. Ha0 Temp., C. 100 G.%zO Urea per Urea er

0 10 20 30 40 50 60

67 84 105 136 163 205 246

70 80 90 100 110 120

309 396 508 725 1164 2244

Solubility in Methanol (IO, 69, 73, 76) --G. Urea per 100 G. Methanol--

Solid phase, Solid phase Temp., C. CO(NHz)z CO(NH~)~.CH;OH

-78 . . . . . . 0.3 -25 -15 -10

0 + 10 15 19 20 30

. . . . . . 10.9 unstable 11.6 unstable 14.2 unstable 17.7 unstable 19.7 unstable 21.4 unstable 22.0 stable 27.7 stable

2 . 9 3.9 4.9 7.7 12.5 16.4 20.5 .. .. . . 35.3 stable 40

50 46.0 stable . . 60 62.8 stable . .

Solubility in Alcohols (76) G. Urea per 100 G. Alcohol

n- 180- 180- 180-

C. (69) m o l no1 no1 s l c o E ~ l alcohol alco%ol Temp., Ethanol Prop- propa- buta- am 1 Capryl All 1

0 10 20 30 40 50 60 70 80 90

2.6 4.0 5.4 7.2 9.3 11.7 15.1 20.2 * .

* .

1.6 2.0 2.6 3.6 4.8 6.2 7.7 9.8 12.3 17.0

. . s'.i . . . . . . . . .. .

23 . .

1.0 1.3 1.7 2.3 3.1 3.7 4.4 5.3 6.3 8.2

0.7 1.2 1.6 2.1 2.7 3.4 4.1 4.9 5.5

.. . . 0.6 .. . . . . . . . .

. . 9 . 5 .. .. . . . . .. . .

Solubilities in Other Solvents Ethyl ether L15-20' C.), g . / l O O cc. 0.0004 (35) Glycerol 15 C ) ./lo0 g. About 50 (68) Pyridine i20-25; :Cf), g . / lOO g. 0.96 (84) 50 aqueous pyridine (20-25 C.), g . / l O O g. 21.53 (68) Et$l avetate (2.50 c.), g./100 g. 0.080 (61) Ammonia. anhvdrous. ~./100 E.: , - -

-26.4' C. +23.9' C. +50.0 C.

25.1 (67) 107.6 315.2

MAY, 1936 INDUSTRIAL AND ENGINEERING CHEMISTRY 5 19

to satisfy our present and forecastable requirements as well as to allow, for the first time, the exportation of urea.

Physical Properties Pure urea is a white, odorless, crystalline solid with a

cool saline taste resembling sodium nitrate. Urea crystallizes from water in exceedingly long, needle-like crystals without definite terminal faces. However, these are usually well developed when urea is crystallized from alcoholic solution.

The material produced in this country is distinguished from imported urea by difference in crystal habit. It is obtained in compact four-sided rhomblike prisms instead of the usual elongated acicular crystals. The domestic urea is termed

crystal urea." Because of its crystal form, crystal urea is freer-flowing, shows less tendency to mat or cake, and occupies about 25 per cent less space for a given weight-factors of importance in handling, measuring, transporting, and storing,

The essential physical properties of urea are presented in Table I.

( 4

Solubility of Urea in Various Solvents When supersaturated solutions of urea in methanol are

rapidly agitated a t 0" C., a solid phase, CO(NHz)&H30H, separates. This molecular compound is less soluble in methanol than urea and is stable below +19.25" C., the transi- tion temperature to urea.

Data on the solubility of urea in various solvents are given in Table 11.

Viscosities of Urea- Water Solutions Chadwell and Asnes (id) showed that, although aqueous

solutions of urea do not have negative viscosities (relative viscosity less than water), their viscosities are much lower than those of equivalent solutions of ether, ethyl and methyl acetates, and urethane in water. The relative viscosities of urea-water solutions are as follows (densities are in paren- theses) :

Temp., I Per Cent by Weight of Urea: 0 c. 0% 5% 10% 15%

5 1.000 1.0000 1.019 1.0150) 1.046 1.0296) 1.086 10444) 1.054 1.0283) 1.094 1 0428 10

25 1.000 (0.9971) 1.038 (1.0106) 1.077 (1.0240) 1.126 (1.0376)

1.000 0 99971 1.021 1.0140 16 1.000 0:QQQl) 1.030 1.01321 1.066 i 1.0273) 1.111 [1:0415] 20 1.000 i 0.9982) 1.033 1.0120) 1.071 (1.0257) 1.118 (1.0396)

Chemical Properties Urea has long been considered as the

diamide of carbonic acid, or carbamide, NH2.C0.NH2. Werner has brought together considerable evidence (86) to show that this conception does not adequately represent the facts either for the syntheses or for the reactions of urea.

He advocates the cyclic formula NH:C(d and visualizes

the transient existence of an active tautomeric enol form,

NH:C

d

520 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 28, NO. 5

all other amides, CO(NHz)z + 2HN02 --+

COz + Nz + 3Hz0 Werner contends that urea and pure nitrous acid do not react

ratio of carbon dioxide to nitrogen (1 to 2) required by the above equation is never obtained. The proportion of carbon dioxide is always much higher and the composition of the

proposed the following mechanism for the reaction in presence of acid:

CO(NH2)z + HNOz + Nz + 2Hz0 + HNCO

disilver urea, CO(NHAg)2. A dimercury urea can be simi- larly prepared (ss). peroxide, co(~H,)z .HzOz, which decomposes a t 85" C. (4). vrea replaces the water of crysta~~isation in many com- pounds. G~~~~~ in the presence of an aqueous solution of

(87) ; similarly, calcium nitrate forms Calurea, CaNOp 4CO(NH&, a well-known fertilizer material.

Hypochlorite, hypobromite, or acid permanganate solutions convert urea into carbon dioxide and

except in the presence of 8 strong acid and that the volume Urea forms a crystalline stable compound with hydrogen

gas is affected by the concentration of reactants (86). Werner urea a t 300 C. is converted to the complex, CaS04.4CO("2)2

OXIDIZING AGENTS. The cyanic acid is decomposed in two ways as fast as it is Neutral 01 alkaline permanganate solutions do not generated, both reactions proceeding simultaneously; the act on urea. Chlorine acts on fused urea to yield cyanuric predominance of one over the other is dependent on the condi- tions : acid, ammoniLlm chloride, and Bromine has a similar action (71) . When chlorine or hypochlorites act on

well-cooled or dilute solutions of urea, chloro- and dichloro- urea are formed [h'H2.CO.PJHC1 and CO(NHC1)21. These

HNCO + HzO --+ NHs + COz HNCO + NHOz e COz + Nz + Hz0

Urea sulfonic acids, NH2CO.NH8OIH and CO(NH- SOsH)2 were prepared for the first time in 1931 (3).

Urea forms crystalline addition compounds with a large number of inorganic and organic compounds. On evaporat- ing a solution containing both urea and sodium chloride, the compound CO(NH2)2.NaCl.H20 separates in shining prisms (melting range, 60-70' C.). Similar complexes are formed with ammonium chloride and salts of copper, silver, gold, magnesium, zinc, cadmium, aluminum, mercury, lead, and most other metals. Over thirty chromium-urea compounds alone have been described.

Urea also forms metallic salts such as mono- or disodium ureas [NHZCO.NHNa or CO(NHNa)z] obtained by the interaction of urea and alkali or alkali amide in liquid am- monia. Aqueous solut,ions of urea act on silver oxide to form

compounds decompose a t 71' and 32' C., respectively, when rapidly heated (7, 15, 21, 64). Through the chloroureas, hydranine can be produced in yields up to 60 per cent (66). The chloroureas decompose in dilute aqueous solutions to yield chloramines, and bichlorourea on treatment with strong ammonia (16, 91) produces p-urazine or diurea,

ORGANIC COMPOUNDS. Urethanes or carbamic acid esters are obtained when urea is heated with alcohols:

NHzCONHz + .ROH + NHz.COOR + NHs This is a general reaction and can also be applied to dihydric and polyhydric alcohols. However, the yields are relatively

MAY, 1936 INDUSTRIAL AND ENGINEERING CHEMISTRY 521

low. Evidently alkyl carbonates, (RO)zCOz, cannot be prepared through the action of 2 moles of alcohol with 1 of urea, the reaction always stopping a t the urethane stage.

Urea reacts with aldehydes, ketones, acid anhydrides, hydrazines, certain esters, and halogen-substituted com- pounds. Two reactions, highly important commercially, are the reaction of urea with formaldehyde and with malonic acid derivatives.

Probably the first observation that urea and formaldehyde condense must be credited to Schiff in 1869 (66). The com- mercially important reaction is the formation of the water- soluble crystalline monomethylol and dimethylolurea : NHzCO.NHZ + CHzO + NHzCO.NHCHzOH (methylolurea)

(dimethylolurea)

Application of heat or catalyst, or both, to the methylolureas causes further reaction, the methylolurea condensing with itself to form larger and larger molecules; as the reaction continues, the product passes from the true-solution state to the colloidal-solution state and finally to the hard, water- insoluble resin. Further treatment of this resin with heat, such as in the molding operation, forms an insoluble, infusible resin.

Astonishingly large amounts of urea are employed in the manufacture of the malonylureas or barbituric acid deriva- tives, widely employed soporifics and sedatives. The malonyl- ureas can be obtained through the interaction of urea and substituted malonic acid esters-for example, diethylmalonyl- urea or diethylbarbituric acid, which as Verona1 or Barbital is obtained from diethyl malonic ester and urea:

NH2.CO.NH.CHzOH + CHzO + CO.(NH.CH?OH)Q

Diethylmalonylurea or diethyl- barbituric acid (Barbital or Ver-

Similarly Allonal contains the allyl isopropyl derivative, Luminal and Phenobarbital the ethyl phenyl derivative, Dial the diallyl derivative, etc. Some four hundred barbituric acid derivatives have been described but only about a dozen are in common use.

Analytical Methods The four principal analytical methods now in use for urea

are the Kjeldahl (6W), urease (SW), hypobromite (WS), and xanthhydrol (30) methods.

The Kjeldahl method is not specific for urea and is appli- cable only when no other nitrogenous materials are present. When concentrated sulfuric acid is used for the digestion, the results are somewhat erratic (78). It has been noted that the use of dilute sulfuric acid (20 per cent by volume) gives good and consistent results.

The hypobromite method, where the nitrogen evolved is measured, is rapid but not accurate.

In the urease method, urea is hydrolyzed to ammonia and carbon dioxide by the enzyme, urease (obtained from the Jack bean, Canavalia ensiformis). This method is specific for urea, but small variations in titration or weighing may cause large percentage errors. For instance, on a 0.1-gram sample, an error of 0.1 cc. of 0.1 N acid introduces an error of 0.3 per cent nitrogen.

Urea forms the insoluble dixanthhydrylurea when treated with a methanol solution of xanthhydrol. This may be weighed or dissolved in sulfuric acid and estimated colori- metrically (5) or titrated with permanganate (53) or dichro- mate (1). The xanthhydrol method is not applicable in the

Urea diethylmalonic ester onal)

presence of cyanamide, since urea is obtained from cyana- mide in the analytical procedure (32).

Literature Cited Allen, F. W., and Luck, J. M., J. Biol. Chem., 82, 693 (1929). Basaroff, J . prakt. Chem., 1, 283 (1870); Ann. Chem. Pharm., 146, 142 (1868); Chem. Soe. J., [2] 6, 194 (1869); 2. Chem., 1869, 204.

Baumgarten and Marggraff, Ber., 64, 301 (1931). Bayer & Co., German Patent 293,195 (July 14, 1916); Beil-

steins Handbuch der organischen Chemie, 4th ed., 1st suppl., Berlin, Julius Springer, 1929.

Beattie, Florence, Biochem. J., 22, 711 (1928). Behal, Bull . soe. chim., 15, 149 (1914). Behal and Detouef, C m p t . rend., 153, 681, 1229 (1911). Blair, J. Am. Chem. Soc., 48, 97 (1926). Blanchard and MacDonald, Action of Nitrous Acid on Subst.

Ureas, paper presented at the Buffalo meeting of the Ameri- r can Chemical Society, September, 1931. Bourgeois, Bull. soc. chim., [3] 7, 45 (1892). Ibid., [31 17, 474 (1897). Bridgman, Proc. Am. Acad. Arts Sci., 52, 91 (1916). Burdick, Chem. & Met. Ens., 40, 638 (1933). Chadwell and Asnes, J . Am. Chem. SOC., 52, 3507 (1930). Chattaway, Am. Chem. J., 41, 83 (1909); Chem. News, 98, 166, 285 (1909); J . Chem. Soc., 95, 235, 464 (1909); Proc. Roy. SOC. (London), 81A, 549 (1909).

Chattaway, Proc. Roy. SOC. (London), 81A, 381 (1908). Clark, Gaddy, and Rist, IND. ENQ. CHEM., 25, 1092 (1933). Clark and Hetherington, J . Am. Chem. SOC., 49, 1909 (1927). Clark and Krase, IND. ENQ. CHEM., 19, 208 (1927). Dalman, J. Am. Chem. SOC., 56, 549 (1934). Datta, J . Chem. Soe., 101, 166 (1912). Davy, Phil . Trans., 102, 144 (1812). De Graaff and others, in Beilsteins Handbuch der organischen

Chemie, 4th ed., 1st suppl., Vol. 3, p. 25, Berlin, Julius Springer, 1929.

Dehn, J . Am. Chem. Soc., 39, 1400 (1917). Emich, Monatsh., 10, 331 (1889). Escales, Chem.-Ztg., 35, 595 (1911). Fawsit, A., 2. physik. Chem., 41, 602 (1902). Fearon, Physiol. Rev., 6, 411 (1926). Fiohter and Becker, Ber., 44, 3473 (1911). Fosse, Ann. inst. Pasteur, 30, 525 (1916). Fourcroy and Vaquelin, Ann. chim., 31,49 (1799). Fox and Geldard, IND. ENO. CHEM., 15, 743 (1923). Franklin, E. C., Nitrogen System of Compounds, p. 115,

New York, Reinhold Pub. Co., 1935. Franklin and Stafford, J . Am. Chem. SOC., 28, 97 (1902). Gortner, Biochem. Bull., 3, 468 (1914). Hantzsch and Hoffman (and Bauer), Ber., 38, 1005,1013 (1905). Hendricks, J . Am. Chem. SOC., 50, 2455 (1928). Henry, J . pharm., 15, 161 (1829). Hoffman, Ber., 4, 262 (1871). Hurd, Pyrolysis of Carbon Compounds, A. C. S. Monograph

International Critical Tables, Vol. V, p. 101, New York,

Ibid., Vol. V. w. 231.

No. 50, p. 607, New York, Chemical Catalog Co., 1929.

McGraw-Hill Book Co., 1929.

(42A) Ibid., Vol. VI, p. 83. (43) Ibid., Vol. VII, p. 245. (44) Jaenecke, 2. Elektrochem., 36, 647 (1930). (45) Kharasch, Bur. Standards J . Research, 2, 359 (1929). (46) Krase and Gaddy, IND. ENQ. CHEM.. 14, 611 (1922). (47) Krase and Gaddy, J. Am. Chem. SOC., 52, 3088 (1930). (48) Krase, Gaddy, and Clark, IND. ENQ. CHEM., 22, 289 (1930). (49) Krase and Hetherington, Ibid., 19, 208 (1927). (50) Lewis and Burrows, J. Am. Chem. SOC., 34, 1515 (1912). (51) Ibid., 34, 1525 (1912). (52) Lucas, R., and Hirschberger, W., 2. angew. Chem., 42, 99 (1929). (53) Luck, J. M., J . Biol. Chem., 79, 211 (1928). (54) MacDowell, J . Am. Chem. SOC., 41, 241 (1919). (55) McBride, Chem. & Met. Eng., 32, 791 (1925). (56) Matignon and Dode, Bull. SOC. chim., [5] 1, 114 (1934). (57) Matignon and Frejacques, Compt. rend., 170, 462, 171, 1003

(1920); 174, 455, 1747 (1924); Bull. soc. chim., 31, 101, 307, 394 (1922); Chimie et industrie, 7, 1057 (1922); Ann. chim. [9] 17, 257, 271 (1922).

(58) Miller and Ditmar, J . Am. Chem. SOC., 56, 848 (1934). (59) Mixter, Ibid., 4, 35 (1882). (60) Parker and Keenen, Chem. & Met. Eng., 39, 540 (1932). (61) Pinck & Kelly, J . Am. Chem. SOC., 47, 2170 (1925). (62) Prout, Ann. Philosophy, 11, 352 (1818). (63) Regnault, Ann. chim. phys., 69, 180 (1838). (64) Rouelle, J . Medicine, Nov., 1773.

VOL. 28, NO. 5 INDUSTRIAL AND ENGINEERING CHEMISTRY

Schestakow, J . Russ. Phys. Chem. SOC., 35, 858 (1903); 37, 5 (1905); German Patent 164,755 (Nov. 2, 1905).

Schiff, Ann., 151, 186 (1869). Scholl and Davis, IND. EXG. CHEM., 26, 1299 (1934). Seidell, A., Solubilities of Inorganic Compounds, 2nd ed.,

Ibid. , suppl. 2nd ed., Vol. 11, p. 1486 (1928). Shnidman and Sunier, J. Phva. Chem., 36, 1232 (1932). Smolka, Monatsh., 8, 64 (1887). Solvay (Slosse), Bull. acad. YOU. Betg., [3] 35, 547 (1898). Speyers, Am. J. Sci., [41 14, 293 (1902). Ibid., 10, 61 (1903). Tanatar, J. Russ. Phys. Chem. Soc., 47, 1283 (1915). Timofeiew, Dissertation, Kharkhov; Seidell, Solubilities of

Inorganic Compounds, 2nd ed., Vol. I, p. 737, New York, D. Van Nostrand Co., (values derived) 1919.

Ullmann, Ensyklopadie der tech. Chemie, 2nd ed., Vol. 6, p. 107, Berlin, Urban and Schwarzenberg, 1930.

Vol. I, p. 738, New York, D. Van Nostrand Co., 1919.

(78) Vee and Davis, IND. ENG. CHEM., Anal. Ed., 7, 259 (1935). (79) Walker and Hambly, J . Chem. Soc., 67, 746 (1895). (80) Walker and Wood, Ibid., 83, 484 (1903). (81) Walton and Wilson, J . Am. Chem. Soc., 47, 320 (1925). (82) Werner, E. A.. J. Chem. SOC., 103, 29 (1913); Ber., 18, 3106

(1885),; 19, 341 (1886); 38, 1010 (1913); Richter, Organic Chemistry, 3rd ed., Vol. I, p. 530, tr. by E. N. Allot, P. Blakistons Son & Co., Philadelphia, 1934.

(83) Werner, E. A., J . Chem. Soc., 103, 1015 (1913). (84) Ibid., 117, 1046 (1920). (85) Ibid., 111, 863 (1917). (86) Werner, The Chemistry of Urea, London, Longmans, Green

& Co., 1923. (87) Whitaker, Lundstrom, and Hendricks, IND. EKG. CHEM., 23,

1281 (1933). (88) Wohler, An%. Phys. Chem., 12, 253 (1828).

RECEIVED March 14, 1036

0 . 0 VACUUM REFRIGERATION HE chemical engineer and refrigerating engineer have a t their disposal a large T variety of industrial refrigerants. New

ones have frequently been added to the list and some have been quickly and widely adopted with considerable success. Water as a refrigerant is by no means new, but its possibili- ties were neglected for many years until recent improvements in the steam-jet type of vacuum producer provided eco- nomical equipment for applying this method.

Chilling water by partial evaporation a t high vacuum has been known for decades. A few isolated cases are recorded

FIGURE 1. REFRIQERATING UNIT OF 24 Tom CAPACITY, WITH VERTICAL VACUUM CHAMBER

D. H. JACKSON Croll-Reynolds Company, Inc.,

New York, N. Y.

where the method was applied in the early part of the century, but the installations proved impractical and were more in the nature of engineering experiments than of practical or eco- nomical installations.

During the past few years a large amount of development work has been done by different manufacturers of steam-jet equipment, and numerous installations have been made for air-conditioning, cooling drinking water for large buildings, and cooling a large variety of fluids in chemical process work. A conservative estimate of the total capacity of vacuum refrigerating equipment installed in the past three years is equivalent to 50,000 tons of ice every 24-hour day. The reason for this rather sudden commercial application of an old, well-known principle is interesting. Many of the early attempts to apply this method depended upon reciprocating vacuum pumps to produce the vacuum and draw off the necessary vapor from the high-vacuum evaporating chamber.

The problem can be easily understood by considering a typical case of chilling water required for air-conditioning a medium-size restaurant. Assuming that the required capacity for cooling and dehumidifying the air is 50 tons of refrigera- tion, a total heat absorption of 600,000 B. t. u. per hour is necessary. Assuming that the required chilled water tem- perature is 45 F., a vacuum corresponding to an absolute pressure of 0.3 inch of mercury is required. Therefore, suffi- cient water must be evaporated a t 0.3 inch absolute so that the latent heat of evaporation will absorb the 600,000 B. t. u. The latent heat a t 0.3 inch is 1066 B. t. u. Dividing 600,000 by 1066 gives 562 pounds per hour of water which must be evaporated. The specific volume of water vapor a t 0.3 inch absolute is 2033 cubic feet per pound. The total volume of vapor to be handled, therefore, is 562 X 2033 or 1,142,546 cubic feet per hour (19,042 cubic feet per minute).

Steam- Jet Apparatus Obviously, then, the vacuum cooling method is not prac-

tical with conventional reciprocating vacuum pumps. This type of pump has its advantages for low and moderate vacua, but it is generally agreed that its efficiency falls sharply a t high vacuum. A battery of dozens of large-size commercial reciprocating pumps would be required for this duty. On