US2481585A - Lubricating oil composition - Google Patents

Description

Patented Sept. 13, 1949 LUBRICATING OIL COMPOSITION Michael W. Freeman, Detroit, Mich.

No Drawing.

Serial No. 616,960

This invention deals with the composition of lubricating mediums. More particularly, it relates to the improvement of lubricating mediums by means of multi-functional complex organic co-reaction products, which when mixed with various amounts of organic lubricating bodies or other neutral mediums produce a transformation in the product, the consistency of which varies from a thin medium to a solid mass, and the transition temperature of which is substantially increased from the non-fluid to the fluid phase. The composition may be used as a lubricating base which is readily soluble in organic lubricating bodies, or may be designed so as to form stable lubricating emulsions with water or-water soluble mediums.

By this invention, lubricants may be prepared to withstand wide temperature changes without marked changes in consistency. For example, a lubricant may be made which withstands temperatures ranging from about minus 100 F. and

. to about plus 400 F. withoutmarked change in consistency or breakdown. Also, stable, high temperature lubricating greases may be prepared without the use of heavy metal soaps, thereby obviating such disadvantages as corrosion, bleeding and soap separation, which usually results in poor lubrication. Such lubricants are especially adaptable for dynamos, pumps, Diesel, truck and airplane engines;

Another object of this invention is to produce a lubricant for tanks, turbines, hypoid gears, and alloy bearings, which are subject to high pressures, high temperatures, excessive friction, oxidation and corrosion.

Still another object of this invention is to employ such composition as an additive in lubricating oils for internal combustion engines, since it possesses properties which inhibit sludge, piston and ring sticking, and varnish and lacquer formation.

A further obect of this invention is to produce an oil or water soluble medium applicable as a machining lubricant, such as for cutting, drilling, reaming, broaching, milling, threading, grinding, hot forging, cold and hot stamping, drawing and for plastic col'd working of metals.

The foregoing and related ends are obtained by producing a co-reaction, in proper proportions, between organic nitrogen base-organic acid reaction product and an oxidized mixture of organic lubricating bodies and organic sulphoccmpounds. These various materials co-react to form a homogeneous compound.

In the term organic nitrogen base organic reaction product, the following are meant to be included: (1) amine organic acid reaction products and (2) quaternary ammonium hydroxide organic acid reaction products. As representative of the first class are the following: a reaction Claims. (01; 252-332) Application September 17, 1945,

product prepared from alkylamines, alkyl polyamines, alkylolamines, polyalkylene polyamines, alicyclic amines, aralkylamines, heterocyclic basic nitrogen compounds, etc. A representative of the second class are: tetra-alkyl ammonium hydroxides, and aryl-aralkyl ammonium hydroxides, etc., with 'various organic acids. These acids may be mono or polycarboxylic acids of the aliphatic and aromatic series; also organic sulphonic acids, such as p-toluene sulphonic acid, paradiphenylsulphonic acid, quinolinesulphonic acid, etc. However, the carboxylic acids aresgenerally more satisfactory.

More specifically, such amines as diethylamine, mono-amylamine, di-amylamine, and triamylamine, di-n-butylamine, monobutylamine, dibutylamine, undecylic amine, laurylamine, myristic amine, palmitylamine, stearylamine, mono, di, and triethanolamine, laurylolamine, palmitylolamine, stearylolamine, .ethylene diamine, diamino-isopropanol, triethylene tetramine, cyclohexylamine, dicyclohexylamine, benzylamine, morpholine, piperidine, pyridine, quinoline, cephalin, lecithin, trimethyl benzyl, ammonium hy-' droxyl, dimethyl-dibenzylammonium hydroxide,

tetraethyl ammonium hydroxide, Alkaterge-O an oil-soluble substituted oxazoline the properties of which are fully described in the Handbook of Material Trade Names by Zimmerman and Lavine and manufactured by Commercial Solvents Corporation, etc., are suitable.

Among the organic acids which are suitabe are: capric, undecylic, lauric, myristic, anachidic, anthranilic, stearic, oleic, palmitic, ricinoleic, linoleic, oxalic, succinic, glutarlc, adipic, sebacic, lactic, maleic, malic, tartaric, citric, benzoic, toluic, cinnamic, salicyclic, peanut-oil fatty acids, soy bean oil fatty acids, hydrogenated soy bean oil fatty acids, hydrogenated fish oil fatty acids, degras fatty acids, naphthenic acids, acids prepared by oxidation of petroleum hydrocarbons,

abietic acid, etc.

condensation products, polyalkylated diphenylsulphonates, higher sulphated secondary alcohols, higher alkyl sulphated alcohols, sulphonated castor oil, sodium taurocholate, etc. More specifically, the following compounds have been found satisfactory: the esters of sulpho-succinic acid, sulphated higher primary alcohols, formaldehyde condensation product of di-isopropylated naphnormally present in the various ingredients.

thalene B sulphonic acid, sodium taurocholate,

sulphonated castor oil, petroleum sulphonic acids miscible in either oil and/or water, di-secondary desired properties.

The oxidizing agents for the organic lubricating bodies-organic sulpho reaction products may be any well-known oxidizing agents, such as air, KMn04, H202, P205, P203, P204, ozone, chromates, organic peroxides, such as benzoyl peroxide, acetyl peroxide, ultra violet rays, X-rays, actinic rays, etc.

It is important to note that during the acid treatment of mineral oil, or other organic lubricating bodies, to produce sulfonates, the action of the acid or of the acid and oxygen of the air upon the organic lubricating body has an oxidizing efiect during the period of reaction. After the sludge and impurities have been removed, the resultant product comprises mixtures 'ofoxidized organic lubricating bodies and its oxidized sulf o compounds. This may be used as such, or the oxidized suli'o compound may be removed by conventional methods which usually'contain from 20 to 80% of the entrained organic lubricating bodies and these may be used to react with the amineorganic acid reaction product to form the desired lubricating complex co-reaction base. If the removed resultant productcontains less than about 1% of reacted oxygen, the product should be subjected to further oxidation. Hence, for purposes of this application and claims, the term oxidized organic lubricating bodies shall comprise bodies subjected to oxidation of the extracted oxidized sulfo components from this treated body. The resultant lubricating complex base may be further commingled with ordinary mineral oil, organic lubricating bodies, or with other than oil soluble medium, such as water, glycerine, glycols, etc.

Since there are a vast number of both. the

used. Usually the temperature varies from room temperature to the boiling point of the component parts, and the time of reaction varies from a fraction of an hour to about eight hours. The amounts of amine and respective organic acid used are related to approximately the molecular weight of each ingredient. In some cases, it is desirable to have present an excess of amine in the final product because of its stabilizing effect, its value in counteracting corrosion, its value in accentuating a desirable phase relationship with the medium which is compounded with it, or to improve the refractive index of the combined composition, or to eflect any combination of the above mentioned functions. The relative amount of oxidized organic lubricating medium sulfo organic compound used varies from approximately equal molecular proportions to about fifty tothe amineorganieacid reaction product. I

Also, in may instances where it is desired to modify organic lubricating mediums other than oil soluble ones, such as water or water soluble substances such as glycerol, ethylene glycol, a1-

' cohol, ketone, esters, aldehydes, etc., the amine is increased above its molecular weight combining power, in order to obtain a more stable and desirable product.

The method of preparing this complex base is simple, requiringno specially designed complex equipment or delicate control. The following examples are used for purposes of illustration and should not be construed in any way as a limitation of the invention.

Method of preparing diethylamine-stearic acid,

oxidized mixture ofmineral oil-organic petroleum sulphonate complex co-reaction Product estimated one to twenty moles of petroleum sulphonate and a light petroleum oil suflicient in amount to solubilize the sulphonate are heated for one to four hours with air being blown amine-organic acid reaction products as well as the oxidized organic lubricating bodies-organic sulpho reaction products, it is obviously impossible to enumerate them all. However, these reaction products may be so chosen that they are relatively miscible in lubricating organic bodies, and if desired, are also miscible in aqueous mixtures.

The amount of the complex co-reaction product will be determined, in general, by the nature of the components used, the medium with which it is admixed, and the characteristics desired of the lubricant. Therefore, the nature of the co-reaction product and the final characteristics desired of the lubricant will in all cases determine the amount of complex co-reaction product to be em-j ployed. Usually from 0.1-50% and, in many through the mixture under constant agitation. At the end of this period, the air is cut of! and the amine-organic acid reaction product is slowly stirred into the oxidized mixture. The entire mixture is reheated and about one to ten parts of oil are slowly added under constant agitation.

The complex co-reaction lubricating base is a flilim jelly and is soluble in mineral lubricating o Method of preparing laurylolamine-oleic acid,

oxidized mixture of mineral oil-organic petroleum sulphonate Approximately one mole of laurylolamine and about one mole oleic acid are reacted at elevated reaction temperature for a period of from a fraction of one hour to two hours in a suitable reaccases, 5-25% of the complex co-reaction lubrieating base may sufllce. For many uses the comtion vessel until a homogeneous mixture is obtained.

In the same or in another vessel, an estimated approximately one to twenty moles of organic petroleum sulphonate and a light mineralpetroleum oil sufficient in amount to solubilize the sulphonate are heated for one to three hours, air being blown through the mixture under constant agitation. At the end of this period, the air is cut oi! and the amine-organic acid reaction product is slowly stirred into the oxidized mixture.-

Method of preparing triethanolamine-deems fatty acid; oxidized mixture of mineral oil-sulphonated castor oil Approximately one or more moles of triethanolamine and about an equivalent amount of one mole of degras fatty acid are reacted at an elevated reaction temperature for a period up to about two hours in a suitable reaction vessel.

In same or in another vessel approximately estimated one to twenty moles of sulphonated castor oil and alight petroleum oil sumcient to solubilize the sulphonated castor oil are slowly heated, and -10% of mo. is carefully added, and the entire mixture is reacted with constant stirring for about an hour. If desired, this reaction product may be used as is or the mixture may be purified by dissolving it in an inert solvent, washing it, removing the aqueous liquid and the inert solvent. The above amine-organic acid reaction product is slowly stirred into the purified or unpurified oxidized mixture of oil-sulpho castor oil mixture, and the entire mixture is heated to an elevated temperature and admixed with from one to ten parts of pale oil.

The complex co-reaction lubricating base is soluble in lubricating oil.

Various other organic reagents can be incorporated with the complex co-reaction base composition either during the mixing process or after it has been compounded in order to enhance lubricating and/or physical properties. Among the desirable additives are halogenated aromatic and aliphatic compounds, sulphurized oils, phosphorus-sulphur oxygen containing organic reaction products, sulphur oxygen containing organic reaction products; phosphorus-sulphurized oil compounds, such as unsaturated petroleum derivatives, olefines, isolefines, diolefines and olefinic polymers, unsaturated fatty bodies which can be either vegetable, animal or mineral type. The phosphorus-sulphur reagents used can be either inorganic or organic compounds, such as: P2S5, P483, P283; phosphorus-oxides, phosphorushalides, phosphorus-oxy-halides, phosphorussulpho-halides, react with unsaturated organic compounds and/or unsaturated fatty bodies. Pour point depressors, such as chlorinated naphthalenes, alkyl-aromatic amines, liquid polymers of dimethyl silicons, and other organic silicons, and organic silicon polymers; corrosive inhibitors, such as inorganic nitrites and organic nitroso and nitro compounds; agents to facilitate dynamic impacts in cold and hot forging, drawing, piercing, or thread grinding, such as the polyvalent metal high molecular weight fatty acid derivatives. Inert materials such as pulverized mica, zonolite, colloidal graphite and the like.

Bearing the above remarks in mind, the following examples serve to illustrate the wide applicability of this base composition.

Method of preparing benzylamine-benzoic acid;

oxidized mixture of organic lubricating bodysulfo succinic acid complex co reaction product Approximately one mole of benzylamine and about one mole of benzoic acid are reacted at elevatedv temperatures for a period of a fraction of one hour to about five hours in a suitable reaction vessel.

In the same or in another vessel approximately about one to five moles of sulfo-succinic acid and castor oil suflicient in amount to solubilize the sulfo compound are heated under agitation in the presence of the oxidizing agent P205 until the desired oxidized mixture is obtained. This oxidized product may be used as is or purified as described in previous example. At the end of this period I the amine-organic acid reaction product is gradually introduced into the above oxidized product, and the entire mixture is reheated and about one to ten parts of oil are slowly added under agitation, or the resultant co-reaction product may be used as lubricant per se.

Method of preparing triethanolamine-oleic acidpetroleum sulfonates containing entrained oxidized mineral oil, soluble in water Approximately one or more moles but not exceeding five moles of triethanolamine and one mole oleic acid are reacted at room or at elevated temperature until a homogeneous product is obtained. To this, approximately one to fifteen moles of petroleum sulfonate (containing from 20-80% entrained oxidized oil) or a mixture of approximately equal parts of mineral oil and petroleum sulfonates containing the above amount of entrained oxidized oil, is slowly added to the amine-organic acid reaction product, and the entire mixture is heated and agitated. About one to three parts of water is then added to form the base composition. Depending upon the machining operation, this base composition can be diluted with from one to fifty parts of water to give an excellent cutting and cooling composition.

Method of preparing triethanolamine-oleic acidpetroleum sulfonates containing entrained oxidized mineral oil, soluble in' oil medium Approximately one or more moles but not exceeding five moles of triethanolamine and one Wide temperature range lubricant Following the procedure outlined in the above examples, approximately molar amounts of diamylamine and benzoic acid were reacted and admixed with approximately one to fifteen moles of petroleum sulfonates (containing from 20-80% entrained oxidized oil), and the entire mixture was heated and agitated until a homogeneous product was obtained. Modifying amounts of ethyl aniline and trichlordiphenyloxide were added, and the product diluted with 1000 see. visc. oil at F.

This product remained plastic at minus 60 I". and had a drop point by the basket method of plus 375 F.

a control test.

Non-corrosive extreme pressure lubricant peratures until the reaction is completed, and.

admix with approximately from one to fifteen moles of petroleum sulfonates (containing from 20 to 80% of entrained oxidized oil). Modifying amounts of phosphorized-sulphurized petroleum oil and/or fatty bodies can be added to enhance extreme pressure properties. sition can be used for thread cutting or grinding, hypoid gears, and in places where extreme pressure and corrosion is encountered. The following-is a partial list of some preferred products which may be compounded as outlined in the illustrated examples; or the procedure may be modified and the proportions may be varied from the above cited examples. I

1. Diamylamine-stearic acid, oxidized mixture of mineral oil-petroleum sulfonates. l 2. Dibutylaminc-benzoic acid, oxidized mixture of mineral oil-petroleum sulfonates.

3. Diethylamine-oleic acid, oxidized mixture of mineral oil-sulpho-succinic acid. I, I 4. Diamylamine-benzoic acid, petroleum sulfonates (containing 20-80% entrained oxidized'oil) 5. Cyclohexylamine-stearic acid, oxidized mixture of carbonyl compounds (glycerine, glycoles) and sodium diisopropyl naphthalene-sulphonate.

6. Triethanolamine-olelc acid, oxidized mixture of mineral oil-ester of sulphosuccinic acid.

7. Diamino isopropanol-oleic acid, oxidized mixture of mineral oil-petroleum sulfonates.

8. Di-n-butylamine p-toluene sulphonic acid, oxidized mixture of mineral oil-petroleum sulio nates.

9. Stearylolamine-oleic acid, oxidized mixture of mineral oil-petroleum sulfonates. 1

10. Benzylamine-linoleic acid, oxidized mixture of mineral oil-esters of sulpho-succinic acidi 11. Laurylamine-oleic acid, oxidized mixture of mineral oil-petroleum sulfonates. j

12. Morpholine-stearic acid, oxidized mixture of mineral oil-petroleum sulfonates.

13. Morpholine-naphthenic acid, oxidized mixture of mineral oil-sulphonate castor oil.

14. Piperidine-sebacic acid, oxidized mixture of mineral oil-petroleum sulfonates.

15. Trimethyl benzyl ammonium hydroxide stearic acid, oxidized mixture of mineral oil-ester,

of sulpho-succinic acid.

16. Triethanolamine-abietic acid, oxidized mixture of mineral oil-petroleum sulfonates.

17. Laurylamine-salicyclic acid, oxidized mix-,

ture of mineral oil-petroleum sulfonates.

18. Stearylamine-naphthenic acid, oxidizedi mixture of mineral oil-petroleum sulfonates.

19. Stearylolamine-naphthenic acid, oxidized mixture of mineral oil-petroleum sulfonates.

20. Laurylamine-degras fatty acid, oxidized mixture of mineral oil-petroleum sulfonates.

21. Stearylamine-toluic acid, oxidized mixture of mineral oil-petroleum sulfonates.

acid, oxidized mixa 22. Diamylamine-benzoio ture of mineral oil-petroleum sulfonates.

Tests the improved oil for three of 340 F. and then exposed to same test was conducted with This base compo- .70 hours at a temperature 1 the atmosphere for 1 48 hours and the time of corrosion noted. The

the reference oil as Improved Control Oil, Time Oil, Time me when corwhen corrosion rosion noted noted Hours Houn A.... 16%laurylolamine-oleic acid oxidized 48exoel- 2.

gnixtture oi mineral'oil-petroleum suilent.

one es. B. l5 diethylamine-stearic acid 011- 40 2.

dized mixture 0! mineral oil-petroleum suiionates. C.-. 15% stenrylamine-naphthenic acid 2.

oxidized mixture 0 mineral oilpetroleum sulfonates. D... 15% triethanolamine-degras iatt 40 2. acid oxidized mixture of mineral o petroleum sulfonates. E Morpholine-stearic acid oxidized mix- 38 2.

Eurot of mineral oil-petroleum sulone cs.

II. Cutting compositions prepared as disclosed in column 6, lines 19 to 59 inclusive, in mineral oil or m'odified'so asto be miscible with water, were used as cutting compounds on different machines cutting and drawing 'variousmetals and metal alloys. After the employment oi. over 100,000 gallons of the base composition, an increase of up to about sevenfold in tool life at a material increase in machining speed and feed hasbeen observedi The products 01' thisainvention in their undiluted form possess strong bactericidal and bacteriostatic' properties. Certain autotrophic bacteria; which are completely'non-pathogenic for man and which have been found as air and soil contaminants in these productsare rendered in capable of multiplication in the undiluted products; when diluted with water or oil, the bacteriostatic properties, with respect to the autotrophio organisms, are reduced and a certain amount of growth occurs.

These products are, however, bactericidal in their undiluted form and strongly bacteriostatic when diluted for the heterotrophic group of organisms which contains pathogenic forms for man. When these products are diluted with water or oil, the bactericidal properties are reduced but the bacteriostatic properties against the heterotrophs remains.

It may be stated then that the bacteria found as contaminants in oil or emulsions containing compositions of this invention do not usually correspond to any, of the bacteria known to be pathogenic for man. Such bacteria as have been found in the products of this invention are non-pathogenic contaminants that "may enter any exposed material from the air, dust, or hands of workers.

The problem of dermititis by the use of products of this invention as cutting compounds is reduced to a minimum.

This composition has an additional advantage in that it i capable cides, such as formaldehyde, creosote, dior tricreosote, etc., so their usual obnoxious and irritating odor is mitigated to practically nil.

This invention has been presented in detail and with numerous examples. This has been done by way of illustration only and with the intention that no limitation should be imposed upon the invention thereby. effected in the practice of the invention which are within the scope of the following claims.

What I claim as my invention is:

1. A lubricating oil composition having incorof masking certain germi-.

Various modifications may be r amas from room temperature to the boiling point the component parts of said reaction, (a) 1 to 5 moles of an organic nitrogen base with about 1 mole of an organic monocarboxylic acid and (b) an oxidized mixture of from 1 to 20 moles of an organic sulionate and a hydrocarbon lubricating body in an amount suflicient to solubilize said organic sulfonate, said portion (11) of the reaction containing not less than 1% of reacted oxygen.

2. A lubricating oil composition having incorand (b) an oxidized mixture of from 1 to moles of an organic sulfonate and a hydrocarbonvlubricating body in an amount sufiicient to solubilize said organic sulfonate, said reaction being carried out at from room temperature to the boiling point of the component reagents taking part in porated therein in an amount suflicient to impart extreme pressure properties to said lubricating oil of a complex reaction product obtained by coreacting, at a temperature ranging from room temperature to the boiling point of the component parts of said reaction, (a) 1 to 5 moles of an organic nitrogen base with about 1 mole of an organic aliphatic monocarboxylic acid having from 8 to 18 carbon atoms and (b) an oxidized mixture of from 1 to 20 moles of an organic sulfonate and a hydrocarbon lubricating body in an amount suflicient to solubilize said organic sulfonate, said portion (b) of the reaction containing not less than 1% of reacted oxygen.

3. A lubricating oil composition having incorporated therein in an amount sumcient to impart extreme pressure properties to said lubricating oil of a complex reaction product obtained by coreacting, at a temperature ranging from room temperature to the boiling point of the component parts of said reaction, (a) 1 to 5 moles of an organic nitrogen base with about 1 mole of an organic aliphatic monocarboxylic acid having from 8 to 18 carbon atoms, and (b) an oxidized mixture of from 1 to 20 moles of an organic petroleum sulfonate and a hydrocarbon lubricating body in an amount suflicient to solubilize said organic petroleum sulfonate, said portion (b) of the reaction containing not less than 1% of reacted oxygen.

4. A lubricating oil composition having incorporated therein in an amount sumcient to impart extreme pressure properties to'said lubrieating oil of a complex reaction product obtained by coreacting, at a temperature ranging from room temperature to the boiling point of the component parts of said reaction, (a) 1 to 5 moles of an organic amine with about 1 mole of an organic monocarboxylic acid and (b) an oxidized mixture of from 1 to 20 moles of an organic suli'onate and a hydrocarbon lubricating body in an amount suflicient to solubilize said organic sulionate.

5. A lubricating oil composition having incorporated a complex coreaction product in an amount so that said lubricating oil remains plastic throughout a wide temperature range of from minus 100 F. to plus 400 F., of (a) 1 to 5 moles of an organic amine with about 1 mole of an organic monocarboxylic acid and (b) an oxidized mixture of from 1 to 20 moles of an organic sulfonate and a hydrocarbon lubricating body in an amount suihcient to solubilize said organic suli'onate, said reaction being carried out at from room temperature to the boiling point oi the component reagents taking part in the reaction, and a four point depressing amount of a polymeric silicon.

6. A lubricating oil composition having incorporated therein in an amount suflicient to impart extreme pressure properties to said lubricating oil of (a) 1 to 5 moles of an organic amine with about 1 mole of an organic monocarboxylic acid,

the reaction, and a germicidal amount of agermicide from the class consisting of formaldehyde, cresol, and phenol.

'7. A lubricating oil having incorporated therein from 0.1 to 50% of a complex coreaction product obtained by coreacting (a) 1 to 5 moles of an alkylolamine and 1 mole of an aliphatic monocarboxylic acid having 8 to 18 carbon atoms and (b) an oxidized mixture of petroleum sulfonate and mineral oil in an amount sunicient to solubilize said petroleum sulfonate, said coreaction being carried out at from room temperature to the boiling point of the component reagents taking part in the reaction.

8. A lubricating oil having incorporated therein from 0.1 to 50% of a complex coreaction product obtained by coreacting (a) 1 to 5 moles of ing part in the reaction.

9. A lubricating oil having incorporated therein from 0.1 to 50% of a complex coreaction product obtained by coreacting (a) 1 to 5 moles of triethanolamine and 1 mole of an aliphatic monocarboxylic acid having 8 to 18 carbon atoms and (b) oxidized mixture of petroleum sulfonate and mineral oil in an amount sufllcient to solubilize said petroleum sulfonate, said coreaction being carried out at from room temperature to the boiling point of the component reagents taking part in the reaction.

10. A lubricating oil having incorporated therein from 0.1 to 50% of acomplex coreaction product obtained by coreacting (a) 1 to 5 moles of diethylamine and 1 mole of an aliphatic monocarboxylic acid having 8 to 18 carbon atoms and (1b) oxidized mixture of petroleum sulionate and mineral oil in an amount sufllcient to solubilize said petroleum sulfonate, said coreaction being carried out at from room temperature to the boiling point of the component reagents taking part in the reaction.

MICHAEL W. FREEMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 722,507 Helmar Mar. 10, 1903 1,892,650 Coleman Dec. 2'7, 1932 1,985,687 Nuesslerin et a1 Dec. 25, 1934 2,049,043 Birkly Jan. 28, 1941 2,239,720 Katzman Apr. 29, 1941 2,303,848 Freeman et al. Dec. 1, 1942 2,340,112 Davis et al. Jan. 25, 1944 2,355,995 Morgan Aug. 15,1944 2,382,699 Duncan Aug. 14, 1945 OTHER REFERENCES Handbook of Material Trade Names,"Zimmerman et al. (1946), pages 21 and 23.