US2916453A - Manufacture of sodium base grease - Google Patents

Description

United States Patent M MANUFACTURE or SODIUM BASE GREASE Roy F. Nelson, Port Arthur, Tex., assignor to Texaco Inc., a corporation of Delaware No Drawing. Application December 22, 1955 Serial No. 554,645

15 Claims. (Cl. 252-41) other properties, including high dropping points, which are also required. The proper texture for greases for this type of service is a smooth short fiber texture with just the right amount of fiber development, since greases of a buttery texture are thrown off the bearings at high speed revolutions, and greases of long fiber or stringy texture tend to rope and feed out of the bearings. Also, greases which are too fibrous are dry and deficient in adhesivenes and lubricating ability.

In accordance with this invention sodium base greases having the texture and other properties required of a very superior wheel bearing grease are obtained by the method which comprises carrying out a limited oxidation treatment upon a saponifiable material comprising a fatty acid glyceride and a high proportion of free fatty acid, in admixture with a minor amount of the mineral lubricating oil forming the oil component of the grease. The oxidized mixture is thereafter saponified and dehydrated at temperatures below the melting point of the soap, suitably below about 350 F., and additional mineral lubricating oil is added following the dehydration and during the cooling process.

Oxidative treatments have been employed heretofore in grease making processes of other types in order to obtain different effects. For example, Kaufman, U.S. 1,966,- 821, U.S. 1,971,750, U.S. 2,002,819 and U.S. 2,084,974, prepared block greases of relatively low soap contents for the required hardness by heating mixtures of tallow, or tallow together with a Small amount of free fatty acid, and the mineral lubricating oil component of the grease in the presence of air for periods up to about 40 hours, and then saponifying the oxidized mass at a high temperature above the melting point of the soap. Also, Dilworth et al., U.S. 2,626,898, obtained an improved ball and roller bearing grease of a buttery texture by carrying out a post-saponification oxidation treatment upon the saponification mass containing free alkali.

The grease making process of this invention produces a grease of very different type from either the block type or the buttery ball and roller bearing greases of the above patents. In addition, it avoids the hardening effect obtained by Kaufman by means of his oxidation treatment in the preparation of block greases, such effect being undesirable in greases of the present type wherein a certain minimum soap content for a given penetration is necessary in order to obtain the required high dropping points and high mechanical stability. In the grease preparation of this invention, a high proportion of free fatty acid as well as a certain amount of glyceride in the saponifiable material is essential for obtaining a grease of the Patented Dec. 8, 1959 desired texture and other properties, and the amount of oxidation is also critical.

This invention contemplates particularly greases having soap contents in about the range 12-20 percent by weight, having penetrations in the range required for No. 2 and No. 3 NLGI grade greases and dropping points above about 400 F. They are substantially anhydrous greases, preferably containing not more than about 0.2 percent of water. The greases may be substantially neutral or they may contain a small amount, such as up to about 0.5 percent by weight, of free fatty acid or of free alkali. They preferably contain not more than about 0.2 percent of free fatty acid and not more than about 0.25 percent of free alkali for a No. 2 NLGI grade grease containing about 12-15 percent of soap, and not more than about 0.35 percent of free alkali for a No. 3 NLGI grade grease containing about 15-20 percent of soap. The greases may contain additives of the usual type such as corrosion inhibitors, oxidation inhibitors, anti-wear agents and so forth.

The saponifiable material employed suitably comprises a mixture of higher fatty acid glycerides and free higher fatty acids wherein the free fatty acid content is about 40-80 percent by weight of the saponifiable material. It preferably comprises such a mixture wherein the free fatty acid content is about 50-70 percent by weight. The fatty acids and fatty acid glycerides comprising the saponifiable material may be any of the higher fatty acids and glycerides thereof which are employed conventionally in grease making, particularly fatty acids containing about 14-24 carbon atoms per molecule and the glycerides of such acids. For best results, the saponifiable material should contain some unsaturated fatty acid material, sufficient to give an iodine value of about 30-80, and preferably in about the range 40-70 to the saponifiable material. Saponifiable materials of too low unsaturated content when employed in this process produce less shear stable greases, while saponifiable materials containing proportions of unsaturated materials above this disclosed range produce greases having lower dropping points and in decreased yields.

The mineral lubricating oils employed in these greases may be either distillate or residual fractions from parafiinic, naphthenic or mixed base crudes, having viscosities in about the range 25-500 seconds Saybolt Universal at 210 F. The oils employed in the saponification mixture and for finishing are preferably oils having viscosities in about the range 50-250 seconds Saybolt Universal at 210 F., which may be blends of lighter and heavier oils of different types. The oil which is employed for finishing, which constitutes the major amount of the mineral lubricating oil employed in the grease, may be an oil of the same type as employed in the saponification mixture or a different oil may be employed such as a lighter or heavier oil of greater or less paraffinicity.

The saponification mixture which is subjected to the oxidation treatment comprises a saponifiable material as described above and mineral lubricating oil in an amount sufiicient to impart fluidity to the mass during the oxidation and subsequent saponification steps. The mixture preferably comprises such a saponifiable material and mineral lubricating oil in a proportion of about 2:1 to 1:2 by weight. The mineral lubricating oil employed may be either a distillate or residual fraction, preferably having a viscosity above about 50 seconds Saybolt Universal at 210 F. It is most suitably a residual oil having a viscosity in about the range -300 seconds Saybolt Universal at 210 F.

The oxidation step is carried out by heating the. saponification mixture in the presence of air at atmospheric or slightly elevated pressure until the desired amount of oxidation has been obtained. It is suitably carried out at a temperature above about 300 R, such as a temperature in about the range 300-700 F., and at atmospheric or increased pressure. At lower temperatures in this range, such as temperatures in about the range 300- 400" F., increased pressures up to about 100 pounds per square inch gauge may be advantageously employed. The process is preferably carried out at temperatures in about the range 400-600 F. and at atmospheric pressure or slightly increased pressures, such as pressures of about -50 pounds per square inch gauge. The length of time required will vary according to the temperature and other conditions employed. When the process is carried out by heating the saponification mixture at a temperature of about 450-500 F. with stirring, in an open kettle or in a semi-closed kettle provided with an air draft, the time required is about 3-8 hours. The time required is greatly shortened by employing increased pressures or by blowing air through the mixture. According to the preferred method of carrying out the oxidation, air is blown through the saponification mixture at a rate of about 0.05 to about 1.5 cubic feet of air per minute per pound of charge while the mixture is maintained at a temperature in about the range 400-500 F.

The amount of oxidation of the saponification mixture which is required to obtain the desired texture and other properties of the grease is, in general, represented by a viscosity increase of the saponification mixture of about 5 to about 35 seconds Saybolt Universal at 210 F. The optimum amount of oxidation within this range varies somewhat with the oxidation conditions employed. When the oxidation is carried out by merely stirring the saponification mixture at a suitably high temperature in the presence of air, the amount of oxidative change required for best results is represented by a viscosity change of from about 15 to 35 seconds Saybolt Universal at 210 F. When the oxidation is carried out by blowing air through the charge, a lower amount of oxidation is required, and optimum results are obtained with a viscosity increase of about 525 seconds, and preferably of about -20 seconds Saybolt Universal at 210 F. when air is blown through the saponification mixture at a rate of about 0.05 to about 1.5 cubic foot of air per hour per pound of saponification mixture.

In accordance with the preferred grease making procedure, the oxidized saponification mixture is mixed with an aqueous sodium hydroxide solution in substantially the required proportion for complete saponification and the saponification mass heated at a temperature in about the range 170-250 F. until the saponification is completed. The mass is then heated ata temperature of about 250- 350 F., and preferably about 280-350 F. for a sufiicient period of time to substantially dehydrate. The heat is then reduced and additional mineral oil is added gradually while the mass is allowed to cool. Any additives employed are added when the grease is at a suitably low temperature.

The following examples are given for the purpose of more fully disclosing the invention.

EXAMPLE I A grease was prepared from an oxidized mixture of Star tallow and mineral lubricating oil. The Star tallow was a commercial material having a saponification number of 198, a neutralization number of 21.4, an iodine number of 59, and a titer, C. of 37.6. The mineral lubricating oil which was employed in the saponification mixture was a propane deasphalted residuum having a viscosity of 176.8 seconds Saybolt Universal at 210 F. from a parafiin base crude.

A mixture of the Star tallow and mineral lubricating oil in about equal amounts by weight was heated with stirring in a semi-closed grease kettle provided with an air inlet and a draft fan for blowing air into the top of the kettle and a stack equipped wtih a water-cooled condenser for returning reflux to the kettle. The mixture was heated to 485 F. in 3 hours and maintained at that temperature for 7 hours with continuous stirring and blowing of air into the kettle.

A 25 pound portion of the oxidized mass obtained as described above was withdrawn to a second grease kettle and cooled to 250 F. It was saponified by adding 3.6 pounds of a 49 percent aqueous solution of sodium hydroxide and maintaining the temperature at 250 F. for one hour. The temperature was then increased and maintained at about 325-340 F. for two hours to dehydrate, after which the mass was allowed to cool while 69 pounds of additional lubricating oil was added gradually to give a 13 percent theoretical soap content grease. The lubricating oil employed for the finishing was an oil having a viscosity at 210 F. of 80.6, comprising a blend of about equal amounts by weight of a paraflinic residuum of the same type as that employed in the saponification mixture and a relatively light naphthenic distillate oil having a viscosity of about 200 seconds at F. The grease was drawn at 150 F.

The product obtained was a grease of very fibrous texture which gave the following tests:

Dropping point, F. 378 Penetration, ASTM, at 77 F.:

Unworked 230 Worked 214 EXAMPLE II A grease was prepared in substantially the same manner as described in Example I, except that stearic acid was employed as the saponifiable material. This material had a saponification number of 102, a neutralization number of 107, an iodine number of and a titer, C. of 52.8.

The stearic acid was mixed in equal parts by weight with a lubricating oil of the same type as that employed in Example I and the mixture heated to 480-490 F. in 3 hours and held at that temperature for 5 hours with continuous stirring and blowing air into the kettle. The following tests were obtained upon the oxidized mixture.

Original Final Sanonification number..- 107 97 Neutralization number... 102 87 Viscosity at 210 F. SUS 02. 8 75.3

Dropping point, F. 424 Penetration, ASTM, 77 .F.:

Unworked 246 Worked 302 As shown by the above example, the desired short fibered texture was not obtained by employing a fatty acid alone as the saponifiable material.

of tallow fatty acids having a saponification number of 206, a neutralization number of 202, an iodine number of 51 and a titer, C. of 40.8. The mineral lubricating oil employed in the saponification mixture was an oil of the same type as that employed in Example I.

The saponification mixture, comprising the saponifiable material and mineral lubricating oil in equal amounts by weight, was oxidized in the same manner as described in Example I. The mixture was heated to 485 F. in 4 hours and then maintained at 480-495 F. for 8 hours longer with continuous stirring. Portions of the mixture were withdrawn at intervals and employed for grease making. The following tests were obtalned upon the withdrawn portions.

- Length of Viscosity Viscosity Sap. Neut. .Fraction No. Time Above at 210 F. Increase No. No.

(Original 65.6 a s2 blend). 2.0 hours-- 77.6 12.0 100 70 5.0 hours 87.1 21.5 94 61 6.5 hours 95.7 30.1 90 57 8.0 hours 112. 3 46. 7 s7 56 The withdrawn portions were employed in the grease making in the manner described in Example I, with saponification at about 250 F. and dehydration at about 300 1 for 2 hours. After the mixture had cooled to 'in' accordance with the method of this invention by employing as the saponifiable material a mixture of free fatty acids and fatty acid glycerides within the disclosed range and by carrying out an oxidation treatment upon the saponifiable mixture so as to obtain a certain limited amount of oxidative change. As shown by the data, the saponification mixture which had been oxidized for only 2 hours at 485? F. produced a grease which was satistfactory with regard to penetration and dropping point but having a more fibrous texture than desired, while the saponification mixture which had received too much oxidation produced a grease which was buttery in texture and too soft.

EXAMPLE IV Another series of greases was prepared employing saponifiable materials comprising freee fatty acids and fattyacid glycerides 'in various proportions and carrying out the oxidation so as to obtain different amounts of oxidative change as measured by the viscosity increase of the saponification mixture. 7

The saponifiable materials were obtained by mixing Star tallow and tallow fatty acids, which were commercial materials of the same character as those employed in Example III, having iodine numbers from about 40 to 60. The lubricating oils employed in the saponification mixture and for finishing were oils of the same types as those described in Example I.

The oxidation was carried out at temperatures in the range 300-500 F. at atmospheric and slightly increased pressures, with air blowing through the charge at rates from about 0.07 to 1.20 cubic feet of air per hour per pound of charge, and with return of all reflux to the kettle.

The saponification and finishing were carried out as described in Example I.

The following table gives representative data for grease preparations of this series.

Table l Grease No 1 saponifiable material: Free fatty 30 acid, percent. Oxidation conditions:

Temperature 485 Pressure, p.s.l.g

Air rate, cu. ft./hr./lb. charge Hrs. to max. temp Hrs. at max. temp Viscosity increase Tests:

Dropping point, F 890 Pena. AS'IM, at 77 F.-

Unworked- Worked Soap, percent Water, percent Grease Texture 0:3 Slightly too fibrous.

278 268 275. 27% 272 15.0 (calc.) 15.8 (calc.)

Slightly stringy.

Good Good Semibnttery below about 300 F., additional mineral oil was added As shown by the table, a grease (No. 1) prepared from of the same type as that employed in Example I .for a saponifiable material comprising only 30 percent free finishing, in sufiicient amount to give a theoretical soap content of 17 percent. The greases, obtained had the following properties:

fatty acids had a too fibrous texture, even though the saponification mixture was oxidized to a viscosity increase of 18.7, whereas a grease (No. 7) prepared from a Oxidized Blend Fraction N o B C D E Dropping point 432 438 432 432. Penetration, AS'IM, at 77 F.:

Unworked 242 325. Worked.-. 250 287 273 Grease texture Too fibrous Excellent smooth Excellent smooth Buttery.

. short fiber. short fiber.

The above'example shows that greases of the desired saponifiable material comprising 90 percent free fatty texture, penetration and high dropping point are obtained acids was slightly stringy, with insufiicient fiber, even though the saponification mixture was oxidized to a .vis-

cosity increase of only 8.9. Grease No. 6, which was prepared from a saponification mixture which had been oxidized to a viscosity increase of 28.3 was borderline with respect to texture. Greases No. 2-5, which are representative of greases prepared under the preferred conditions of this invention, possessed the desired smooth, short fiber texture, as Well as worked penetrations in the desired range and high dropping points.

EXAMPLE V Another grease preparation representative of the preferred method of the invention was carried out by blowing air through the saponification mixture during the oxidation treatment and employing as the saponifiable material a tallow containing about 65 percent of free fatty acids.

The tallow was a commercial material having a saponifiable number of 197, a neutralization number of 126, an iodine number of 57 and a titer C. of 41.0. A typical analysis of a material of this character is as follows: 2.0 percent myristic acid, 32.5 percent palmitic acid, 14.5 per cent stearic acid, 48.3 percent oleic acid, 2.7 percent linoleic acid, and the glycerides thereof.

The mineral oils employed in the grease preparation were oils of the same types as those employed in Example I. The oil employed in the saponification mixture was a 22.0 API gravity oil having a viscosity of 177.7 seconds Saybolt Universal at 210 F., a pour point of 90 F. and a flash point of 565 F. The oil employed for finishing was a 22.0 API gravity oil having a viscosity of 79.3 seconds Saybolt Universal at 210 F., a pour point of l F. and a flash point of 385 F. i

The saponification mixture, consisting a a blend of equal parts by weight of mineral lubricating oil and tallow was charged to a Stratco Pressure Soap Contactor, which is a vessel containing a concentric inner cylinder having a vaned outer wall and an impeller at the bottom. The impeller was rotated during the oxidation process at a rate of 500 rpm. so as to obtain very uniform and rapid mixing. The oxidation was carried out at atmospheric pressure and a maximum temperature of 485 F. by bubbling air through the charge at a controlled rate of 0.4 cubic foot per hour per pound of charge for two hours while the charge was heated from 120 F. to 485 F., and then for an additional hour while the temperature was maintained at 480-485" F. The viscosity of the saponification mixture increased during this treatment from an original viscosity of 67.4 seconds to 78.3'seconds Saybolt Universal at 210 F.

A 25 pound portion of the oxidized blend at room temperature was charged to a grease kettle and heated with stirring to about 220 F. While the temperature was maintained at about 220 F., 4.05 pounds of 49 percent aqueons solution of sodium hydroxide were added slowly with continuous stirring. The mixture was then heated at about 250 F. for one hour and the temperature thereafter increased to about 325 F. to dehydrate. The heat was then reduced and 19.9 pounds of lubricating oil as described above were added slowly while the temperature of the mass was maintained at 300 F., after which the heat was cut off and an additional amount of the oil sutlicient to cut the soap content to 13.9% was added gradually while the mass cooled below 300 F.

A smooth short fibered grease of excellent texture and appearance was obtained which gave the following tests:

Dropping point, F. 424 Penetration, ASTM, at 77 F.:

Unworked 245 Worked 287 Soap, percent 13.9 Free alkali, percent 0.14 Free fatty acids, percent 0 Water, percent Trace Shell roll test:

CRC wheel hearing test:

Miniature penetration 4 65 Original Hub 64 Leakage 0 The Shell roll test of the above table is carried out by subjecting the grease to a rolling action by means of weighted roll rotated within a cylinder at 178 rpm. for 4 hours at room temperature. Micropenetrations are obtained upon the original grease and upon the rolled sample. A change in penetration of less than in this test is regarded as satisfactory.

The CRC wheel hearing test is carried out in a simulated front wheel hub and spindle assembly including a leakage collector ring and encased in an insulated cabinet equipped with a heater. A gram sample of the test grease is charged to the bearings and hub, and the hub assembly turned at 440 rpm. for 6 hours at 220 F. spindle temperature. After the test, the amount of leakage is determined by the increase in weight of the leakage collector ring. Miniature penetrations are taken upon the original sample and upon the grease from the hub after the test.

As shown by the above data, the grease which was prepared in accordance with the method of this invention was satisfactory in its resistance to change in the Shell roll test and was outstanding in its resistance to change and to leakage from the hearings in the CRC wheel bearing test.

Greases of substantially the same composition as the grease of Example V have been prepared very satisfactorily in both No. 2 and No. 3 NLGI grades in plant manufacture by the method of this invention. These greases have given excellent lubrication with very low low leakage in commercial use as wheel bearing greases in heavy trucks and buses.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. The method of preparing a lubricating grease which comprises providing a mixture of a mineral lubricating oil and saponifiable material having an iodine number below about 80, consisting essentially of higher fatty acid and higher fatty acid glyceride and wherein the free fatty acid content is about 40-80 percent by weight, heating the said mixture in the presence of air at a temperature in about the range 300-700" F. until the viscosity has increased by about 5-35 seconds S.U. at 210 F., saponifying the said mixture with sodium hydroxide at a temperature within about the range 170-250 F., heating the saponified mass at about 250350 F. for a sufiicient period to substantially dehydrate it, and thereafter reducing the heat and adding additional mineral lubricating oil as the mass is allowed to cool gradually.

2. The method of claim 1 wherein the said saponifiable material is heated in the presence of air until its viscosity has increased by about 5-25 seconds S.U. at 210 F.

3. The method of claim 1 wherein the saponifiable material comprises in major proportion at least one C fatty acid and the glyceride of such an acid.

4. The method of claim 1 wherein the saponifiable material has an iodine value of about 30-80.

5. The method of preparing a lubricating grease which comprises providing a mixture in about a 1:2 to 2:1 ratio by weight of a lubricating oil having a viscosity of about -300 seconds S.U. at 210 F. and a saponifiable material having an iodine number below about 80, consisting essentially of higher fatty acid and higher fatty acid glyceride and wherein the free fatty acid content is about 50-70 percent by weight, heating the said mixture in the presence of air at a temperature in about the range 300-600 F. until the viscosity has increased about -35 seconds S.U. at 210 F., then saponifying the said mixture with sodium hydroxide at a temperature of about 170-250 F. raising the temperature of the saponified mass to about 280-350 F. to substantially dehydrate, thereafter reducing the heat and adding additional mineral lubricating oil as the mass is allowed to cool gradually.

6. The method of preparing a lubricating grease which comprises providing a mixture in about a 1:1 ratio by weight of a paraflinic residual oil having a viscosity of about 150-200 seconds S.U. at 210 F. and a saponifiable material consisting of tallow fatty acids and tallow, having an iodine number in about the range 30-80 and wherein the free fatty acid content is about 50-70 percent by weight, heating the said mixture at about 300- 500 F. in the presence of air until its viscosity has increased by about 5-25 seconds S.U. at 210 F. then saponifying the said mixture with sodium hydroxide at a temperature of about 170-250" F., raising the temperature of the saponified mass to about 280-350 F. to dehydrate the said mass to below about 0.2 percent of water, thereafter reducing the heat and adding additional mineral lubricating oil having a viscosity of about 75-100 seconds S.U. at 210 F. in sufiicient amount to give a soap content of about 12-20 percent by weight as the mass is allowed to cool gradually.

7. The method of claim 6 wherein air is blown through the said saponification mixture during the heating at a rate of about 0.05-1.5 cubic feet of air per hour per pound of said saponification mixture.

8. The method of claim 6 wherein the said saponification mixture is heated in the presence of air until its viscosity has increased by about 10-20 seconds S.U. at 210 F.

9. The method of claim 6 wherein the said saponifiable material has an iodine value of about 40-60.

10. The method of claim 6 wherein the said saponifiable material has a free fatty acid content of about 60-65 percent by weight.

11. The method of claim 6 wherein the oil employed for the finishing following the dehydration is a mineral oil comprising about a 1:1 by weight blend of a heavy paratfinc residual and a lighter naphthenic distillate oil.

12. In the preparation of a sodium base lubricating grease by the method which comprises saponifying a saponifiable material with sodium hydroxide in the presence of a portion of the mineral oil contained in the finished grease, dehydrating the saponification product obtained and adding additional mineral lubricating oil to give the desired grease consistency, the improvement which comprises carrying out a presaponification treatment upon a mixture of the said saponifiable material having an iodine number below about 80, consisting essentially of about 40-80 percent by weight of higher fatty acid and the remainder higher fatty acid glyceride, and mineral lubricating oil comprising a minor portion of the oleaginous liquid component of the finished grease, said treatment comprising heating the said mixture in the presence of air at a temperature in about the range 300-700 F. until a viscosity increase of about 5-35 seconds S.U. at 210 F. is obtained.

13. The method of claim 12 wherein the said saponifiable material has an iodine value of about 30-80.

14. The method of claim 12 wherein the said mineral lubricating oil has a viscosity in about the range -300 seconds S.U. at 210 F.

15. In the preparation of a sodium base lubricating grease by the method which comprises saponifying a saponifiable material with sodium hydroxide in the presence of a portion of the mineral oil contained in the finished grease, dehydrating the saponification product obtained and adding additional mineral lubricating oil to give the desired grease consistency, the improvement which comprises carrying out a presaponification treatment upon a mixture in about a 1:2 to 2:1 ratio by Weight of the said saponifiable material, consisting es- 1 sentially of about 50-70 percent by Weight of higher fatty acid and the remainder higher fatty acid glyceride and having an iodine value of about 30-80, and mineral lubri eating oil having a viscosity of about 100-300 seconds S.U. at 210 F., said treatment comprising heating the said mixture in the presence of air at about 300600 F. until a viscosity increase of about 5-25 seconds S.U. at 210 F. is obtained.

References Cited in the file of this patent UNITED STATES PATENTS 1,966,821 Kaufman -July 17, 1934 1,971,750 Kaufman Aug. 24, 1934 2,002,819 Kaufman May 28, 1935 2,084,974 Kaufman June 22, 1937 OTHER REFERENCES Manufacture and Application of Lubricating Greases- BonerReinhold Pub. Co., NY. (1954), pp. and 126.

Claims (1)

1. THE METHOD OF PREPARING A LUBRICATING GREASE WHICH COMPRISES PROVIDING A MIXTURE OF A MINERAL LUBRICATING OIL AND SAPONIFIABLE MATERIAL HAVING AN IODINE NUMBER BELOW ABOUT 80, CONSISTING ESSENTIALLY OF HIGHER FATTY ACID AND HIGHER FATTY ACID GLYCERIDE AND WHEREIN THE FREE FATTY ACID CONTENT IS ABOUT 40-80 PERCENT BY WEIGHT, HEATING THE SAID MIXTURE IN THE PRESENCE OF AIR AT A TEMPERATURE IN ABOUT THE RANGE 300-700*F. UNTIL THE VISCOSITY HAS INCREASED BY ABOUT 5-35 SECONDS S.U. AT 210*F., SAPONIFYING THE SAID MIXTURE WITH SODIUM HYDROXIDE AT A TEMPERATURE WITHIN ABOUT THE RANGE 170-250*F., HEATING THE SAPONIFIED MASS AT ABOUT 250-350EF. FOR A SUFFICIENT PERIOD TO SUBSTANTIALLY DEHYDRATE IT, AND THEREAFTER REDUCING THE HEAT AND ADDING ADDITIONAL MINERAL LUBRICATING OIL AS THE MASS IS ALLOWED TO COOL GRADUALLY.