ASTM D128 standard test methods for analysis of lubricating grease
INSOLUBLES, SOAP, FAT, PETROLEUM OIL, AND UNSAPONIFIABLE MATTER
12. Choice of Test Method
12.1 Examine greases containing residuum, asphaltic oils and asphalt, tars, and so forth, using Test Method II, as these ingredients usually cause stubborn emulsions if a vigorous agitation process is applied at the start. Analyze all other greases using Test Method I. (See Fig. 1.)

Test Method I

13. Insolubles
13.1 If insolubles are present (see Note 5), weigh the sample (see section 6) in a small beaker, add 50 mL of HCl (10 %), and warm the beaker on a steam bath, stirring until all soap lumps have disappeared and the upper layer is clear. If undissolved mineral matter or other insoluble is present, filter both layers while warm through a Gooch crucible provided with a suitable mat, wash the beaker and crucible with warm (60 to 63°C) water (see Note 6) and n-hexane, (Warning - Extremely flammable. Harmful if inhaled. May produce nerve cell damage. Vapors may cause flash fire.) Finally, wash the crucible with alcohol (Warning - Flammable. Denatured. Cannot be made nontoxic.) collecting the alcohol washings separately, and discarding them. Dry the crucible and contents at 120°C and weigh, reporting the result as percentage of insoluble matter (graphite, molybdenum disulfide, and so forth).

NOTE 5 - If no insolubles are present, omit the procedure given in Section 13.

NOTE 6 - Throughout the test method where the word warm is used, it is to be understood that a temperature of 60 to 63°C is to be used.

14. Soap
or by the single-phase procedure as described in 14.3. In either case, if the contents of the flask or beaker remain liquid, follow the procedure described in 14.4. If contents congeal, or if, in the case of the two-phase decomposition, solid particles form, follow the procedure described in 14.5.

14.2 Weigh the grease sample (see Section 6) into either a 250-mL or a 500-mL Erlenmeyer flask, spreading the sample over the lower inside surfaces of the flask. Add 20 mL of n-hexane followed by 50 mL of HCl (10 %) and several boiling chips. Digest the sample by boiling under a reflux condenser until it is completely decomposed. Formation of a clear oil layer is evidence of complete decomposition. A digestion time of 3 h is generally sufficient; however, more vigorous boiling or use of a stronger HCl solution or additional n-hexane will be found necessary for greases difficult to decompose. Allow the contents of the flask to cool to room temperature.

14.3 Weigh the grease sample (see Section 6) into a 250-mL beaker. Add a TFE-fluorocarbon-coated magnetic stirring bar, 50 mL of t-butyl alcohol (Warning - Flammable liquid; causes eye burns), 50 mL of n-hexane, 2 drops of butter yellow indicator (Warning - Flammable. Vapor harmful) and 2 mL of HCl (37 %). For heavy greases, 50 mL of toluene (Warning - Flammable. Vapor harmful) may be substituted for n-hexane. Note also that t-butyl alcohol will solidify if the temperature is approximately 24 to 27°C or below. Heat the beaker and contents on a magnetic stirring hot plate. Stir magnetically and break up large lumps with a glass rod, but avoid boiling the solution. If the indicator becomes yellow, add concentrated HCl (37 %) in 1-mL increments until the color remains red. Continue the heating and stirring until all grease has dissolved, which indicates complete decomposition. For most grease, 10 to 15 min are usually sufficient. Disregard any inorganic salts that may precipitate. Cool the contents of the beaker to room temperature.

14.4 Transfer the contents of the flask or beaker to a separatory funnel, using n-hexane and water as washing liquids. Allow this solution (or the combined filtrate and washings, except the alcohol washings, from the determination of insolubles, Section 13, transferred to a separator), to clear and draw the aqueous layer, A, which contains all the bases as well as glycerin, into another separator. Wash the n-hexane layer, B, three times with 25-mL portions of water to remove HCl, adding the washings to A. Wash the aqueous solution, A, twice with 20-mL portions of n-hexane, C, and then set Solution A aside for examination for glycerin (Section 16). Wash Solution C once with 15 mL of water, which may then be discarded, and add C to B. If Solutions B and C are comparatively light-colored, an approximate determination of free fatty acids and fatty acids from soap can now be made by titrating the solution in the separator with 0.5 N alcoholic KOH solution (Warning - Poison. Causes eye and skin damage) using phenolphthalein (Warning - In addition to other precautions, avoid skin contact or ingestion) as the indicator, and using 200 as the average neutralization value of the fatty acid (that is, 1.0 g of fatty acid requires 200 mg of absolute KOH for neutralization). If Solutions B and C are dark, add a few drops of 14.1 If insolubles are absent, decompose a sample of the grease, either by the two-phase procedure as described in 14.2 phenolphthalein solution and sufficient 0.5 N alcoholic KOH solution to make the alcoholic layer distinctly alkaline after vigorous shaking.

NOTE 7 - Capital letters reference solutions given in Fig. 1.

14.5 Heat the contents of the flask or beaker to approximately 63°C and transfer to a separator that has been previously warmed by flushing with warm water, using warm n-hexane and warm water as washing liquids (Warning - see 14.5.1). Allow this solution to clear and draw the aqueous layer, A, which contains all the bases as well as glycerin, into another separator. Wash the n-hexane layer, B, three times with 25-mL portions of warm water to remove HCl, adding the washings to A. Wash the aqueous solution, A, twice with 20-mL portions of warm n-hexane, C, and then set Solution A aside for examination for glycerin (see Section 16). Wash Solution C once with 15 mL of warm water, which can then be discarded, and add C to B. If SolutionsB and C are comparatively light-colored, an approximate determination of free fatty acids from soap can now be made by titrating the solution, which is at approximately 63°C, in the separator with 0.5 N alcoholic KOH solution using phenolphthalein as the indicator, and using 200 as the average neutralization value of the fatty acid (that is, 1.0 g of fatty acid requires 200 mg of absolute KOH for neutralization). If Solutions B and C are dark, add a few drops of phenolphthalein solution and sufficient 0.5 N alcoholic KOH solution to make the alcoholic layer distinctly alkaline after vigorous shaking.

14.5.1 (Warning - Extreme care should be exercised in handling warm n-hexane because of pressure developing in the stoppered separatory funnel. Invert the funnel and release pressure through the stopcock occasionally.)

14.6 If Solutions B and C from 14.4 and 14.5 have been titrated, add 0.5 to 1.0 mL excess of alkali before separating. The conservative addition of alcohol at this point can aid in securing rapid and sharp separation. Allow the two solutions to separate sharply and draw off the lower alcoholic layer, D, into another separator. Wash the upper n-hexane layer, E, three times, with 30, 25, and 20 mL of neutral 50 % alcohol, respectively, adding these washes to D. Wash Solution D with 25 mL of n-hexane, after which draw off D into a beaker and add the n-hexane to E. Evaporate Solution D to a small volume to remove alcohol, wash the residue of potassium soap into a separator with hot water, acidify with HCl, and shake out twice with 50 and 25 mL of ethyl ether, F, respectively. Run Solution F into another separator and wash twice with 20-mL portions of water, which can then be discarded. Transfer Solution F to a weighed beaker and evaporate to dryness on a steam bath, blowing with air to remove all traces of ethyl ether. (Warning - Extremely flammable. Harmful if inhaled. May cause eye injury. Effects may be delayed. May form explosive peroxides. Vapors may cause flash fire. Moderately toxic. Irritating to skin.) Heat the residue, consisting of free fatty acids and fatty acids from soap, for a short time on a steam bath, adding and evaporating 5-mL portions of acetone (Warning - Extremely flammable. Vapors may cause flash fires) until a constant weight is obtained and the last traces of water are removed. Determine the exact neutralization value on as large a sample of these fatty acids as possible.

14.7 The fatty acids may be identified to some extent by special tests, such as odor, crystal form, melting point, iodine number, color reactions, and so forth.

14.8 If the grease is appreciably oxidized, the fatty acids obtained by the ethyl ether extraction are likely to be dark in color and hard to identify. For further study and identification, the neutralized acids may be extracted again (qualitatively) with n-hexane and HCl (1 + 3), thus eliminating the small amount of more darkly colored matter.

14.9 From the total quantity of fatty acid found, deduct the free acid, if any (see Section 23), and calculate the remainder as a percentage of soap as described in Section 15.

15. Calculation and Report
15.1 Calculate and report the neutralization number, molecular weight of fatty acids, and percentage of soap in accordance with 15.1.1-15.1.6:

15.1.1 Neutralization Number of Fatty Acids - Calculate the neutralization number of the fatty acids as follows:
A = 56.1BN/X
where:
A = neutralization number of fatty acids,
B = millilitres of KOH solution required for titration of the solution,
N = normality of KOH solution, and
X = grams of fatty acid titrated.

15.1.2 Molecular Weight of Fatty Acids - Calculate the molecular weight of the fatty acids as follows:
Mf = 56,100/A where:
Mf = mean molecular weight of fatty acids, and
A = neutralization number of fatty acids.

15.1.3 Soap in Single-Base Greases—Calculate the percentage of soap in single-base greases as follows:
Soap, % = MsC/MfE
where:
Ms = mean molecular weight of the soap,
C = percentage of fatty acids from soap,
Mf = mean molecular weight of fatty acids from soap, and
E = number of moles of fatty acid per mole of soap.

15.1.4 Soap in Mixed-Base Greases Soluble in Organic Solvents - If the grease is soluble in organic solvents, determine the more accurately determinable metal (of the two soaps present) in the solvent-soluble portion (see Note 8). Then calculate the percentage of the soap having this metal as the base, as follows:
Soap, % = FMs/Mm
where:
F= percentage of the metal determined,
Ms = mean molecular weight of the soap of the metal, and
Mm = molecular weight of the metal.

Calculate the fatty acids necessary to form this amount of normal soap. Subtract these acids from the total soap fatty acids and then calculate the remaining soap fatty acids to the soap of the second metal, as described in 15.1.3.

NOTE 8 - The soluble portion may be separated from the insoluble matter by continuous extraction through an extraction thimble.

15.1.5 Soap in Mixed-Base Greases Not Soluble in Organic Solvents - If the grease is not soluble in organic solvents, determine the more accurately determinable metal and correct for free alkali if it is the predominant metal. Then proceed in accordance with 15.1.4. The presence of insolubles can introduce complications in the analysis of such a grease.

15.1.6 Soap in Greases Containing Heavy Metal Soaps - In greases containing soaps of lead, aluminum, and so forth, the soap content cannot be calculated accurately because free fatty acids, for which correction must be made, are not directly determinable in the presence of such soaps. A good estimate of the soap content may be obtained, however, by adding the value for organically combined metal to that for free fatty acids plus fatty acids (free and from soap) to soap. If the acids are greatly in excess of those necessary for the normal soap of the metal, it is advisable to calculate the metal to normal soap and report the remaining acids as excess acids.

16. Glycerin (Qualitative)
16.1 To determine whether a grease has been made from whole fats or from fatty acids, neutralize Solution A with dry Na2CO3 (Warning - Harmful if swallowed. May cause skin irritation) and add sufficient excess to precipitate calcium or other metals. Then evaporate the whole mass to dryness, extract the residue several times with alcohol, filter the combined alcoholic extracts, and evaporate the alcohol. The residue will then contain most of the glycerin with a little sodium chloride (NaCl). The presence or absence of glycerin in the residue shall be confirmed by suitable qualitative tests.

17. Fat
17.1 Concentrate the n-hexane solution, E (see Section 14), containing free fat, petroleum oils, and unsaponifiable matter to a volume of about 125 mL in a 300-mL Erlenmeyer flask, adding 10 mL of 0.5 N alcoholic KOH solution and 50 mL of neutral alcohol, and boil on a hot plate with an air condenser for 1 1/2 h. Titrate the uncombined alkali with 0.5 N HCl, and from the alkali consumed, corrected for the blank determination as specified in 6.1, calculate the percentage of free fat, using 195 as the average saponification value (that is, 1.0 g of fat requires 195 mg of absolute KOH for specification).

17.2 Place the titrated solution, G, in a separator, draw off the alcoholic lower layer, H, into another separator, and remove the remaining traces of soap as described for Solutions B and C (see Section 14), making only two washes with 30 and 20 mL of 50 % alcohol, I. Combine Solutions H and I, wash once with a little n-hexane, which is added to Solution G, and then evaporate Solutions H and I to a small volume and isolate the fatty acid as described for D (see 14.6). The percentage of fat can be checked by weighing and titrating the free fatty acid.

NOTE 9 - Multiplying the weight of fatty acid by 1.045 gives very close approximation of the weight of fat from which it was derived. This factor varies very little with the molecular weight of the fat.

18. Petroleum Oil
18.1 Evaporate the n-hexane solution, G, now containing all the hydrocarbon oils and unsaponifiable matter, to dryness in a weighed beaker as described for F (see 14.6), weigh the residue, and report the result as petroleum oils plus unsaponiflable matter.

18.2 The viscosity of the petroleum oil can be determined using Test Method D445. If a complete characterization of the petroleum products is required, decompose a new sample of from 150 to 200 g of grease as described in Section 13, except that all quantitative operations shall be omitted, as well as the isolation of the free fatty acids, and the use of standard alkali and acid is not necessary.

18.3 If the grease contains rosin oil, beeswax, degras, montan wax, or other materials containing a large amount of unsaponifiable substances, the petroleum oils isolated from Solution G will contain the unsaponifiable matter, and the physical properties will differ from those of the petroleum products used in making the grease. In most cases, no further separation is possible except in the hands of skillful and experienced operators, who can devise special methods to suit the individual conditions.

Test Method II

19. Dark Greases
19.1 Weigh the sample in a 76-mm (3-in) porcelain dish, and add 10 g of granulated KHSO4 (Warning - Poison. Harmful or fatal if swallowed. Causes severe eye and skin irritation or injury. Dust or mist may be harmful), 10 g of clean, dry ignited sand, and 5 mL of water. Heat the dish and contents on a steam bath, while stirring frequently, until all water is driven off, 2 h usually being sufficient. After cooling and breaking up lumps with a small pestle, transfer the mixture quantitatively to an extraction thimble, which has been previously placed in a Soxhlet apparatus, using a little n-hexane to wash the last traces into the thimble. Extract the thimble thoroughly with n-hexane, concentrate the extract somewhat if necessary, and titrate the free fatty acid and fatty acid from soap with 0.5 N alcoholic KOH solution as in Solutions B and C, 14.4. Proceed in accordance with Sections 14, 17, and 18.

20. Asphalt and Tarry Matter
20.1 Extract the thimble a second time with CS2 (Warning - Extremely flammable. Poison. Vapor may cause flash fire. Vapor harmful. Capable of self-ignition at 100°C or above. Harmful or fatal if swallowed. May be absorbed through the skin.) Evaporate the extract to dryness, heat at 120°C for 1 h, and then weigh, reporting the results as asphaltic and tarry matter. Discard the residue in the thimble.