Commercial Oils, Vegetable and Animal: With Special Reference to Oriental Oils

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Preface

This book is intended primarily for the non-technical man in the oil trade. The writer has attempted to give in it the technical data and information required in every-day dealings in the oil trade, without mixing in a great mass of more or less purely scientific matter.

Trade rules and specifications have been given whereever such exist. The characteristics of the various oils (or constants as they are sometimes less properly called) which are given, are the maximum and minimum values within which most of the samples of oil that will be met with in practice will lie. In general, values which represent what might be termed " freaks " have been omitted. The idea has been to show what values can reasonably be expected, rather than to show the widest variations that can exist. In preparing these maximum and minimum values, determinations of many chemists have been compared, as published in standard text such as Lewkowitsch and Allen, in the technical press, and other sources.

The data on Oriental oils, which are now being imported at Pacific Coast ports, are for the most part results of work in the author's laboratory. Characteristics of these oils have been given separately from the above-mentioned average characteristics. This has been done because it has been found in many cases that a

Vi PREFACE

so-called Oriental oil will dififer from the same oil from other parts of the world, to which the oil trade has been more accustomed in times past. In some cases this is due to difference resulting from climate, soil, and other natural conditions. In other cases it is due to the handling the oil receives, sometimes the result of carelessness, and sometimes due to unavoidable commercial conditions.

The result in some cases is an oil different in some respects from the oil that commerce is used to. Objection is often made by buyers to such differences. But these Oriental oils have filled a great need in a crisis in the United States, and have won a place for them- ' selves, and as such must be accepted by the oil trade. Buyers must not attempt to make Oriental oils conform to the standards of oil from other countries, but should rather draw new standards for these oils, which will fit their special characteristics.

There is a constant demand for closer grading of these oils. This demand will gradually be met as methods for obtaining and shipping these oils improve. In a commercial movement as new as this is, too much must not be expected at the start. The grading is now probably as close as can be under present methods of handling. Cooperation between buyer and seller will be the best means of improving conditions, and of holding this new trade for the United States in years to come.

I. F. Laucks.

Seattle, Sept., 1918.

Chapter I

Definition — General Properties — Rancidity and Free Fatty Acids — Oil Cake — Refining— Physical and Chemical Properties and Reactions of Oik — Moisture or Water — Insoluble Sediment, Dirt, Foreign Substance — Specific Gravity — Melting-, Solidifying-, and Freezing-points — Refractive Index — Color — Viscosity — Saponification Value or Number (Koettstoerfer No.) — ^Iodine Number — Reichert-Meissl, Reichert-WoUny Number — Acetyl Value — Free Fatty Acids and Acid Value or Number — Unsaponifiable Matter — Qualitative Tests — Color Tests — Examination of the Fatty Acids — Cholesterol and Sitosterol (Phytosterol) — Examination of Oils for Purity i

Chapter II

Perilla Oil — ^Linseed Oil, Flaxseed Oil — Proportion of Oil in Seeds — Boiled Linseed Oil — China Wood Oil, Chinese Tung Oil, China Nut Oil — ^Heat or Coagulation Test for China Wood Oil — Japanese Tung Oil, Japanese Wood Oil — Candle Nut Oil, Lumbang Oil— StilUngia Oil, TaUow Seed OU— Hemp Seed Oil — ^Walnut Oil — Soya Bean Oil — Poppy Seed Oil — ^Sunflower Oil — Com Oil — Cottonseed Oil — Sesame Oil, Rape Oil, Colza Oil— Ahnond Oil— Peanut Oil— Tea Seed Oil— Olive Oil— Castor Oil— Animal Oils— Fish Oils— Menhaden Oil — ^Japanese Sardine Oil, or Fish Oil — Sardine Oil — Salmon Oil — Herring Oil — Liver Oils— Cod Liver Oil — Shark Liver Oil— Dogfish Liver Oil — Blubber Oils — Whale Oil— Turtle Oil— Porpoise Oil— Dolphin Oil— Terrestrial Animal Oils — Silkworm Oils, Chrysalis Oil — Egg Oil— Neat*s-foot Oil— Pabn Oil— Cacao Butter- Chinese Vegetable Tallow— Palm Nut Oil, Palm Kernel Oil — Cocoanut Oil — Japan Wax — Animal Fats — Bone Fat— Tallow— Beef Tallow— Horse Fat— Butter Fat- Butter Substitute — Renovated Butter — Waxes — Sperm Oil — ^Solid Waxes — Camauba Wax — Wool Wax or Wool

Grease — Beeswax — Spermaceti — Insect Wax 30

vu

Viii CONTENTS

Chapter III ^

Uses op Oils— Edible Oils— Salad Oils— Edible Fats— Oils for Medicinal Purposes — Burning or Illuminating Oils — Paint Oils — Lubricating Oils — Wool Oils, Cloth Oils — Hydrogenated or Hardened Oils or Fats — Boiled Oils — Varnishes — Enamels — Paints — Blofcm Oils, Oxidized Oils — Rubber Substitute, Vulcanized Oils — Nitrated Oils — Sulphonated Oils — Candles — Fatty Acids — Soap Stock Fatty Acids — Soap — Glycerin — ^Polishes — Foots, Soap Stock — Greases — Sod Oil, Degras io6

Chapter IV

Sampling — ^Tank Cars — Barrels — Cases — Storage Tanks — Seeds,

Cake 119

Chapter I

Vegetable and animal oils, and fats (as distinct from mineral oils, or petroleums), are compounds of carbon, hydrogen and oxygen which are found naturally in all plants and animals.

The word oils is generally applied to the varieties liquid at ordinary temperatures, and fats, to those solid at ordinary temperatures. Oils and fats are chemical combinations of glycerin as a base with the so-called fatty acids.

The combination forms the so-called neutral oil or fat. There is a large number of different kinds of fatty acids. The different kinds of oils found in nature are due to the number of fatty acids. Any one oil generally has some one kind of acid predominant in it, and along with this predominant acid it wiU have besides a number of the other acids in smaller amounts. The different acids each have different properties, and impart these differences to the oils in which they occur. No one oil, however, has any fixed combination of the different fatty acids present in it, but the proportions of these will vary with the locality, soil, season, food (in the case of animals), and various other factors. This accounts for differences between the same species of oil from different places, or harvested at different times.

Examples of the fatty acids, with their occurrence are as follows:

Butyric acid, butter.

Valeric add, porpoise.

Laurie acid, cocoanut, palm nut.

Palmitic acid, palm, and other vegetable and animal fats.

Stearic acid, animal and vegetable fats.

Arachidic acid , peanut .

Oleic acid, most vegetable and animal oils and fats.

Erucic acid, rape, fish.

Linolic acid, drying oils.

Lmolenic acid. Unseed and other drymg oils.

Ricinoleic acid, castor.

It must not be supposed that any of the above acids are the only acids in the oils named. Thus cocoanut oil, besides lauric acid, will contain stearic, palmitic, oleic, etc., in varying proportions.

General Properties

All oils are Ughter than water. When pure they are colorless, but most commercial oils are yellow, or even of darker colors due to impurities. Oils are odorless and tasteless when pure, the taste and odor of commercial oils being due to impurities.

Oils are insoluble in water, but readily soluble in ether, chloroform, benzene, carbon bisulphide, carbon tetrachloride, turpentine, petroleum oils and spirits. They are only partially soluble in alcohol (except castor oil).

They do not give off inflammable vapors imless they are quite hot. They will bum with a wick. They will not distill like petroleum, but decompose imder strong heat.^

If kept from the action of air, light and moisture, oils will remain imaffected for great lengths of time. Oils have been foimd imchanged which were buried for several thousaads of years in ancient tombs.

Oils absorb oxygen from the air. The oils classified as drying oils rapidly absorb oxygen, becoming thick and forming hard fihns. Linseed oil is an example. The non-drying oils absorb oxygen at a slower rate, and become rancid in the process (see later discussion of rancidity). Moisture and light also cause formation of rancidity.

Rancidity and Free Fatty Acids

The property of an oil developing rancidity and free fatty acids is so important commercially that it is worthy of special attention. Rancidity means practically a disagreeable smell and taste in an oil. When an oil turns rancid the free fatty acids increase. Rancidity and free fatty acids are not, however, synonymous terms, as rancidity is not due to the free fatty acids, but to other substances formed from them.

An oil is a combination of glycerin and fatty acids. When moisture and ferments are present in an oil, the combination of glycerin and fatty acid is gradually broken up, so that part of the glycerin^ and part of the fatty acids are present in a free state. This part of the

• Glycerin being soluble in water, when free is generally in the water portion of an oil, except when present in large amount. See p. 87.

fatty acids is called the free fatty acid of the oil. This action increases with time. Some oils turn rancid much quicker than others. As an example of what, increase may occur in storage of oils the following results obtained in the author's laboratory are quoted:

Oil.

Free Fatty Acids.

Fish

Whale

Castor

Peanut

Extracted bean Refined rape. . .

Shark liver . . . .

Turtle

Cocoanut

February.

Per Cent.

11.28

9.02

7.47 7.19

1.20

.63 .63 •52

.14

•35 .14

.14

.14

4.23

6.63

3.74

July.

9-59 7.90

8.11

1.20

1.62

.99 1.20

.21

35 .14

.21

.14

4.30 6.13 9.24 4.02

Increase.

•57

•43

•92

.0

.99

The above samples were stored in tight tin cans at an average temperature of 65° F.

From these results it will be seen that there is considerable variation in the increase of the acids, both between diflFerent oils and, also, between different samples of the same oil. These differences depend largely on the degree of refining and care in preparation, and also on the amount of moisture present.

The free fatty acids when acted upon by oxygen of the air and light develop other compounds of bad smell and taste. It is these latter compounds that cause rancidity in an 9il. Of course the higher the percentage of free fatty acids the more opportunity there is for the formation of the substances causing rancidity.

Perhaps the most common fatty acid in oils is oleic add, which is present in some amount in practically all oils. For this reason the percentage of free fatty acid as determined by analysis is usually expressed as oleic acid.

The free fatty acid of cocoanut oil is sometimes expressed as lauric acid, as this acid is present in cocoanut oil in large amoimt. Percentage of oleic acid is converted to lauric acid by multiplying by 0.71. To convert percentage as lauric to oleic multiply by 1.4 1. Likewise the free fatty acid of palm oil is sometimes expressed in terms of palmitic acid. To convert percentage as oleic acid to percentage as palmitic acid, multiply by 0.91. To convert palmitic to oleic, multiply by I.I.

Classification

Lewkowitsch classifies fats and oils according to the readiness with which they absorb oxygen, i.e., their "drying'' properties, and, according to whether they are of animal or vegetable origin, as follows:

I. Liquid Fats or Oils: A. Vegetable oils.

I. Drying oils: linseed, perilla, timg or Chinese wood, soya.

2. Semi-drying oils; cottonseed, com, sesame,

rape.

3. Non-drying oils: peanut, olive, castor,

almond.

B, Animal oils.

1. Marine animal oils.

a. Fish oils: menhaden, salmon, sar-

dine, herring.

b. Liver oils: cod, shark.

c. Blubber oils: whale, porpoise, seal,

turtle.

2. Terrestrial animal oils: neat^s-foot, silk-

worm oil.

II. Solid Fats:

A, Vegetable fats. Palm, cacao butter, cocoanut,

Japan wax.

B. Animal fats:

1 . Drying fats : icebear, rattlesnake.

2. Semi-drying fats: wild duck, horse, rabbit. 3 Non-drying fats: lard, tallow, butter.

The waxes which are related to fats are classified as follows:

1. Liquid waxes — sperm oil.

2. Solid waxes.

1. Vegetable — camauba, raphia, palm.

2. Animal — ^beeswax, spermaceti, Chinese wax,

wool wax.

It will be noted that sperm oil and spermaceti are properly classed as waxes.

Preparation of Oils and Fats from their Raw Materials

In general the methods of obtaining oils and fats are simple. Only the general methods will be discussed here. Any special methods affecting the commercial properties of an oil will be mentioned mider the description of that particular oil.

The general methods are the following:

(i) Refidering — that is, heating the oil-containing material with water or steam, until the oil exudes from its enclosing cells, and collects on top of the water. It may then be separated. This may be carried out in tanks heated by coils, or in digesters, i.e., boilers into which live steam is injected.

Rendering is chiefly used for animal fats, as lard, tallow, whale oil, and is of little importance for vegetable fats. (See cocoanut oil.)

(2) Expressing. This process ik chiefly used for vegetable oils. The machines used have been gradually improved from primitive trituration in mortars or wedge presses, to the modem hydraulic press. The process consists simply of forcing the oil out of its cells by pressure. The hydraulic press is the common means of applying the pressure, though crude native methods are still used in some coimtries.

Practically all edible vegetable oils are obtained by expression, and expression of such oils is done at as low temperature as possible. Oils for technical uses are expressed hot. More oil is obtained from seeds when expressed hot. The quality is, however, poorer. The first oil expressed is the lowest in free fatty acids and of the best quality.^

The quality of the oil expressed also depends on the quality of the seeds. The oil in the seeds may become rancid, just as it does after it is pressed. Seeds should be kept dry, well ventilated and out of bright light. Moisture especially will cause the formation of free fatty acids in the seeds and the development of rancidity.

(3) Extracting. In this process the oil is dissolved out from other accompanying material by some solvent, in which the oil only dissolves. Such solvents are gasoline (or petroleum ether which is a light gasoline), carbon bisulphide, carbon tetrachloride, benzol, chloroform, acetone, ether. Only gasoline and carbon bisulphide are used on a large scale, the other solvents being too expensive. Extraction processes cannot be used for obtaining oils for edible purposes, as a bad ta3t2 will be left in the oil, no matter how carefully or thoroughly the solvent is afterwards separated. Such oils can only be used for technical purposes.

It sometimes happens that the natural odor and flavor of a crude oil prevent the determination by smell and taste whether the oil is extracted or not. If, however, such an oil be refined and deodorized for edible use, the taste and smell of the solvent remaining would be detectable. Chemical methods will give the final answer as to whether an oil is extracted or not.

The solvent used in extracting the oil is, of course,

^ Two, three, and sometimes more expressions are often made, the first cold, and succeeding ones at higher temperatures. Often expressing is followed by extraction with solvents.

used over and over again. It is separated from the dissolved oil by distillation. A small loss of solvent occurs.^

Oil Cake

The residue left after the oil has been extracted by Dne of the foregoing methods is called the cake. Cake from expression processes still contains considerable oil; in some cases as much oil is left in the cake as has been obtained. The amount of oil left in the cake depends on the raw material, temperature, pressure and type of machine used. Cakes from extraction processes contain very little oil.

Cakes are used for stock food and fertilizing purposes. Not all cakes can be used for stock food. Some, as for example castor seed cake, contain poisonous substances. Cakes from extraction processes are sometimes used as cattle food, but generally are not favored for such use, and find their main outlet as fertilizers. The oil left in the cake becomes of value when it is used as a stpck food, but has no value when used as a fertilizer.

A stock food is valued on the following components: (The last three being more or less detrimental.)

1. Oil or fats.

2. Carbohydrates, including starch and sugars.

3. Proteids, or nitrogen containing substances.

4. Indigestible matter, called " crude fiber."

5. Mineral matter, or ash.

6. Moisture.

A fertilizer is valued differently, as follows:

* Extraction yields higher amounts of oil than expression. Extraction by laboratory methods yields practically 100 per cent of the contained oil. Conmiercially the yields are somewhat lower.

1. Nitrogen (or ammonia).

2. Phosphoric acid, or bone phosphate.

3. Potash (as K2O).

4. Moisture.

Nitrogen is the chief fertilizing value in oil cakes.

Refining

Oils, as first obtained, generally contain impurities in the form of fiber and mucilaginous matter, moisture, dirt or insoluble sediment, free fatty acids, etc., and in order to make the best grade, need refining. Refining is done by a number of different methods.

Standing for some time settles out much of the sediment, water, fiber, mucilaginous matter. Standing cold is especially efficacious as some of the impurities are only slightly soluble in oil at low temperatures. Washing out the oils with boiling water is another method of getting rid of some of the mucilaginous matter. Free fatty acids are removed by treatment with alkalies.

Filtration through such substances as fuller's earth, charcoal, etc., is used to clarify and decolorize oils, especially for edible purposes. Treatment with sulphuric acid is used for rape and linseed oils. There are a number of bleaching processes using chemicals. Chlorine, bleaching powder, bichromates, sulphites have been used, along with a number of others. Bleaching by oxygen is done either by exposure to air and sunUght, or the oxygen is introduced as a gas or as ozone.

Edible oils are, in general, the best grade of any oil produced, and need special attention in their preparation and refining. The raw material must be fresh and of the best grade, and the oil extracted as quickly as possible after harvesting. The oil of first expression, being of the best quality, is used for edible oil. Refining is done by clarifying by fuller's earth^ or animal diarcoal, and free fatty acids are removed by alkalies. Aside from this, however, no chemical processes of bleaching or refining can be used for edible oils. The clarifying and refining takes out, besides the free fatty acids and insoluble matter, any substiinces such .as ferments which would cause later development of free fatty acids and rancidity.^

It is not desirable that edible oils should congeal at low temperatures, that is, they should not deposit a solid fat. The oil is therefore cooled by refrigeration, whereupon the " stearine '' settles out or is filtered out. The oil which remains liquid will not deposit any further sediment. This is " winter oil," so-called because it used to be held over wintertime in order to separate out the " stearine."

\ " Stearine " is the name applied to fats which settle out of liquid oils. These fats are of higher melting-point than the bulk of the oil in which they occur.

Practically any vegetable oil may be used for edible purposes, except certain ones which contain poisonous substances, such as China wood or tung oil, castor, candle-nut and croton. Aside from such consideration then the judgment as to whether an oil is edible or not rests on its taste and smell.

1 Fuller's earth is a mineral product resembling clay in its chemical composition. It has a great absorbent power for coloring matter, hence its value in clarifying and decolorizing.

2 The loss in weight due to taking out all these substances by refining is called the refining loss. It may be determined in the laboratory ai^oximately. See also specifications for cottonseed, peanut, etc.

12 COMMERaAL OILS

Some oils may contain a much higher percentage of free fatty acids than others, and still be edible. Also an oil with no free fatty acids may not be desirable because of a flat taste.

Many attempts have been made to deodorize fish oils to render them fit for edible uses, but so far without much success. Cod liver oil seems to be about the only fish oil that is taken internally, and that without much pleasure.

Oils should be stored at as low a temperature and be kept as free from moisture as possible. If kept from air, tight and moisture, oils will keep indefinitely, as has been shown by oils buried with mummies in Egyptian tombs, which have not developed free fatty acids in several thousand years.

Physical and Chemical Properties and Reactions of Oils

Under this head will be discussed briefly a number of technical methods which are used in the examination of oils to determine their quality and purity.

It must be understood that there is no absolute method

of determining the purity of an oil, all of the methods

used being comparative. For instance, if a chemist is

called upon to determine the purity of a sample of table

salt, he can determine absolutely the percentage of

sodium chloride present, and also the percentage of

■•"""■ities. Such absolute and exact methods are not

able in the case of oils unfortunately.

judging the purity of an oil we have to depend on

atperience. Certain properties of oils, which are

" constants " or " characteristics " have been

to have always the same values (within certain limits) for the same oil. Whenever then, a sample of oil is examined, these characteristics are determined. If their values correspond to the values which the oil in question has been found to possess by past experience, then we conclude it is pure. If the values of the characteristics diflFer radically from past experience, suspicion is at once thrown upon the purity of the oil. Various special tests are then used to confirm the presence of adulteration.

Other properties are called *' variables." The values of the variables vary with the purity, rancidity, age, etc., of the oil. Still other methods of examination are used for accidental impurities.

Important characteristics of oils are: iodine number, saponification number, refractive index, viscosity, specific gravity, titer.

Variables are free fatty acids, color, unsapomfiable matter, acetyl number (except in the case of castor oil where it is a characteristic). Accidental impurities are water, insoluble matter.

Moisture or Water

The determination of water is important from the buyer's standpoint, because he does not wish to pay for water at the same rate as oil. The presence of water also causes oil to become rancid more quickly. Some oils can hold up to about J per cent of water and still be clear. Above that amount the presence of water is shown by turbidity. Various crude methods are used for estimating water, but their results cannot be depended on for all oils. Special apparatus and care is necessary for the exact determination of water.

Insoluble Sediment, Dirt, Foreign Substance^

Includes solid non-fatty matter, remains of animal or vegetable tissue, sand. The determination is important in the case of crude oils which have been prepared without much care.

The specific gravity of any one oil will always be very nearly the same. For instance, the specific gravity of soya bean oil from many sources will vary from .922 to .926 at 15.5° C, but will seldom, if ever, fall outside these limits.

Specific gravity is the ratio of the weight of a given volume of oil (or any other substance) to the weight of the same volimie of water, the specific gravity of which is arbitrarily called i.oo. For example, the weight of a gallon of soya bean oil is .922 the weight of a gallon of water, and so on.^

Specific gravity also varies with the temperature, and is less, the hotter the oil. (This, of course, is due to expansion of volume by heat.) For this reason, to be comparable, specific gravities always have to be determined at some one agreed-upon temperature. This temperature, whenever possible, is 15.5° C, or 60° F. To change specific gravities taken at any other temperature to that at 15.5° or 60° F. the factor of .00064 for each degree Centigrade, or for each 1.8° F.^ is to be

^ Also called impurities.

* See p. 133 for weight per gallon of various oils. ' One degree on the Centrigrade thermometric scale is equivalent to 1.8 degrees on the Fahrenheit scale. See p. 134.

either added or subtracted, depending on whether the oil is hotter or cooler than the standard temperature.

If a chemist should report to you a gravity taken at 25.5° C. and you wished to change it to compare with one at 15.5° C, multiply .00064 by 10 = .0064, and add the product .0064 to the specific gravity determined at 25.5° C. The sum will be the specific gravity at 15.5° C. Specific gravity of all oils is less than i, ranging from .910 to .965 with some of the waxes above or below (sperm oil) these limits. The determination of specific gravity is important in establishmg purity.

Specific gravity is also sometimes expressed by certain empirical scales as degrees. Such a scale is Baum6's scale, which is sometimes used for oils, and very commonly used for petroleimi oils. For liquids lighter than water the Baimae degree nimiber increases, the lighter the liquid becomes. A table showing the comparison between the Baume scale and specific gravity is given on page 133.

Melting-9 Solidifying-, and Freezing-points

Neither of these properties is very important in the examination of oils to determine purity. The freezing-point is important in the examination of lubricating oils.

The melting-point of oils and fats is not of much value as an indication of purity, as it is hard to determine by an invariable method, and also the melting-point of natural oils and fats varies considerably.

The melting-point of the fatty acids prepared from an oil is more constant, and is used especially on hard fats.

The soUdifying-point of an oil is rarely taken. The same remarks apply as for melting-points. The solidifying-point of the fatty acids is more definite. The titer test is one way of determining the solidifying-point of the fatty acids. It is done under certain standard conditions, that may be exactly duplicated by two chemists working independently.

When the fatty acids solidify, a thermometer immersed in them drops to a certain point at which there occurs a small rise as solidification commences. After this the thermometer again drops. The top point of the rise is taken as the " titer " or " titre." Titer is expressed in degrees Centigrade. This test is much used on lard and tallow to detect foreign admixture. It is also valuable in the examination of fats for candle-making purposes.^ Titer is a characteristic of the fatty acids of an oil or fat, and as such may be used to establish purity.

The pour test, used for lubricating oils, is used to determine the temperature at which the oil remains liquid, as this point is of considerable importance for such oils. It is carried out under standard conditions.

Cold tests^ or cloud tests are used to determine the temperature at which solid matter or stearine separates out of an oil, or the temperature at which an oil will remain clear without such separation. They are used in the case of cottonseed, neat's-foot and sperm oils.

Refractive Index

This is a characteristic of liquid fats or oils which is based on certain properties of the oil in deflecting a beam of light passing through the oil. This deflection can be measured (by an instrument called a refractometer) and aflFords a method of determining whether an oil is pure or not. Refractive indices should be taken as a standard temperature (which is usually 40° C). The temperature at which the determination is made should always be stated.^

Color in vegetable and animal oils is generally judged by the eye, except in the case of cottonseed oil and some other refined edible oils. Color is determined by an instnunent called the Lovibond tintometer. This is an apparatus for matching definite shades of color with the oil under examination, so that its color may be definitely stated.

Cottonseed has for a long time been bought and sold on definite color determinations.^ At the present time the tendency is to specify definite colors on other edible oils ds soya, cocoanut and peanut.

The Interstate Cottonseed Crushers Association has adopted a standard bleaching test, which determines the color to which an oil, first refined by alkali, can be afterwards bleached by a standard fuller's earth.

Viscosity

Viscosity may be defined as the internal friction of an oil, or its resistance to flow. Oils vary in this property and it may be used in the examination of oils to detect adulteration. It is especially valuable in the examination of lubricating oils. Viscosity is usually measured