Opinion is divided as to the advisabilit_Edible fats and oils

for a chemical property such as the Reichert value. Although such

a limit as is fixed in Belgium excludes all doubt in condemning

samples that fall below it, yet, as was found in the case of lard (p.

64), a fixed standard leads to an increase in the amount of petty

adulteration, since it is not difficult for a skilful mixture to be

made that will answer the requirements of a moderate standard.

In any case there is even now a systematic attempt to conform with what

the adulterator presumes will be the standard by which the analyst

will judge his product, and the present writer has frequently examined

samples with a Reichert-Meissl value of 23-24 which in all probability

contained a small quantity of foreign fat, but yet might conceivably

have been genuine butter containing less than the average quantity of

volatile fatty acids.

Nor does it follow that such butter is necessarily inferior as a food,

for there is no proof that a slight deficiency in the amount of the

glycerides of volatile fatty acids affects the nutritive value of the

whole fat.

=Cocoanut Oil in Butter.=—The addition of cocoanut oil to butter, which

has become increasingly prevalent of late years, has the effect of

lowering the Reichert-Meissl value to a much smaller extent than the

addition of animal fat.

This is due to the fact that cocoanut oil has itself a Reichert-Meissl

value of 7-8, indicating the presence of a considerable amount of

soluble volatile fatty acids, and it is therefore possible to prepare a

mixture of animal fat, cocoanut oil, and fluid vegetable oil, which can

be added to butter in a fairly large proportion without reducing the

Reichert-Meissl value of the latter below 24 or 25.

The problem of detecting cocoanut oil in butter has therefore received

much attention of late, and numerous methods have been devised for

estimating the amount of such addition.

Speaking generally, these are based upon the fact that cocoanut oil

contains a high percentage of lauric acid (up to 60 per cent.), whereas

that acid is only present in very small proportion in butter fat.

Now, since lauric acid will volatilise in a current of steam, but,

unlike the lower fatty acids (butyric, caproic, caprylic, and capric

acids), is not soluble in water, it is possible to obtain a measure of

its proportion by continuing the distillation as in the Reichert-Meissl

process until the whole of the volatile fatty acids (soluble and

insoluble) have passed over. The distillate, when filtered, is

separated into a soluble and insoluble portion, and the latter may

be dissolved in alcohol and its acidity determined by titration with

standard alkali solution.

A method whereby the process of distillation is greatly accelerated is

described in Chapter VIII.

Other methods of detecting cocoanut oil have been based upon the

quantitative separation of the lauric acid in the form of various

metallic salts, such as barium, cadmium, etc., so as to obtain

“barium values,” “cadmium values,” etc., which will increase with the

proportion of cocoanut oil in the butter.

These methods, however, are more complicated and no more effective than

the method of extended distillation, although they are of value as

affording confirmatory evidence of the adulteration (see p. 116).

=Artificial Colouring Matters.=—The nature of the food given to the

cows, their breed, and the season of the year, all have an influence

upon the colour of the butter; that produced in summer, for instance,

being more yellow than that produced later in the year.

When exposed to the action of air and light the natural colour of

butter gradually fades, and ultimately the fat becomes colourless.

The popular demand for a butter of pronounced yellow colour—a demand

inspired by the belief that intensity of colour indicates purity—has

led to the artificial colouring of pale butter.

The colouring matters employed for this purpose include that of the

carrot, annatto, turmeric, saffron, marigold, and various aniline

dye-stuffs.

Special azo dye-stuffs, soluble in oil, are frequently used, especially

in the United States. They may be detected by mixing a little fuller’s

earth with the butter-fat which has been separated from the curd, the

earth assuming a pink or light red coloration in the presence of such

dyes.

Since in the United States the sale of margarine containing artificial

colouring matters is prohibited, the desired yellow colour is now

frequently obtained by the use of palm oil, mustard-seed oil, and

similar fats of intense colour. Special tests have therefore been

devised for the detection of these fats in butter.

CHAPTER V

LARD

=Rendering of Lard.=—Lard may be defined as the fat separated for use

as food from the adipose tissue of the pig.

In the process of rendering lard the tissue is first finely divided or

minced in a machine, or is crushed between rollers, and is then heated

either by dry heat or by means of steam to expel the fat from the

ruptured fat-cells.

A product of excellent quality is obtained by subjecting the mass

to dry heat at a temperature just sufficient to melt the fat; and a

process of this kind is frequently used in the preparation of the fat

for margarine.

At higher temperatures some decomposition of nitrogenous compounds in

the adipose tissue takes place, and special means must be provided for

carrying off the obnoxious vapours thus produced.

The use of steam in a steam-jacketed pan or digester enables the

temperature to be regulated with greater nicety, and prevents the fat

being overheated and acquiring a burnt flavour.

A more rapid process of rendering lard is to heat the finely divided

material with water in a suitable vessel and subsequently to skim off

the fat that rises to the surface. At first the temperature is kept as

low as possible in order to separate the portions of the fat of lowest

melting-point. Then the temperature is raised, with the result that a

fat of greater consistency rises to the surface; and finally the water

is brought to the boiling-point to separate, as far as is possible by

this means, the residual fat. In this way a fractionation of the lard

takes place.

A process more frequently employed than the preceding one is that in

which the adipose tissue is rendered, in a closed vessel or digester,

capable of resisting the action of steam introduced under pressure.

Numerous patents for apparatus embodying this principle have been taken

out, especially in the United States, various modifications of the mode

of heating, separation of the fat, and filtration being claimed.

In some of the largest works in Chicago and other centres of the

American lard industry a great number of such digesters is employed,

some of them having a capacity of upwards of 20,000 gallons. Each of

these vessels is reserved for its particular kind of fat, so as to

facilitate the speed of working.

In a typical digester the finely minced fatty matter, which has been

separated from the recently killed animal, is introduced from above

through a man-hole, which is then screwed down hermetically. Within the

digester is a perforated false bottom upon which the material rests,

and beneath this is a perforated steam coil, connected by means of

a pipe with an outside boiler, from which steam is admitted until a

pressure of about four atmospheres is shown upon the gauge. Condensed

water is drawn off through a cock near the bottom of the vessel, while

a similar cock is provided near the top for testing whether the fat

is being liberated. After a digestion of about twelve hours the steam

supply is shut off, and the pressure in the digester reduced by opening

the safety valve. Then, after standing for some time for separation

to take place, the aqueous layer is drawn off through taps arranged

at different levels near the bottom. The rendered fat, which has

separated on the surface as a melted layer, is next withdrawn, and

finally the residual mass is expelled through an outlet in the bottom,

which can be controlled from above by a rod passing through the body of

the apparatus.

=Commercial Grades.=—In the United States (which probably produces more

lard than the rest of the world put together) various grades of lard

are recognised, depending mainly upon the part of the animal whence

they were derived. Thus, according to Wiley (U.S. Dept. Agriculture,

Bull. 13), the following descriptions of lard are known in the trade:—

(1) _Neutral lard_, which is the product of the absolutely fresh leaf

of the hog, rendered at a temperature between 105° and 120° F. It is

chiefly used in the manufacture of margarine.

(2) _Leaf lard_, prepared from the residue left after removal of

neutral lard at a lower temperature.

(3) _Choice steam lard_, or _Choice lard_, obtained from the residual

tissue from neutral lard and from adipose tissue from the back of the

animal.

(4) _Prime steam lard_, which may be the product of any part of the

animal, and especially of the fatty tissue from the head, heart, and

intestines.

(5) _Guts_, a low grade of lard rendered from scraps from any part of

the animal, with the exception of the heart and lungs.

In addition to these, still lower grades of pigs’ fat, which are

used for soap and other technical purposes, are separated from hogs

that have died on their way to the slaughter-houses, or from refuse

material. These include _white_, _brown_, and _yellow grease_, and

_pigs’ foot grease_.

The product known in Germany as _pure lard_ is obtained by a process of

steam-rendering, followed by mechanical agitation of the separated fat

in a closed vessel until it begins to solidify. An addition of a small

proportion of a more solid lard is then made, or, in the best grades,

a small proportion of lard stearin is added. According to Voigtländer

(_Zeit. angew. Chem._, 1898, 857), this treatment, which is known as

the Hungarian process, prevents the lard becoming fluid on keeping.

American lard, even when free from any addition of vegetable oil, is

often of a more fluid character than European lard, this being due

partly to differences inherent in the hogs and partly to the influence

of the food given to the animals.

=Composition.=—Lard, like most natural products, shows wide variations

in its chemical and physical characteristics, and this increases the

difficulty of basing definite conclusions as to purity on the results

of analyses. Even in the case of the same animal wide variations are

observed in the composition of fat taken from different parts of the

body, as is shown below.

Chemically considered, lard may be said to consist of glycerides of

stearic, palmitic, lauric, and myristic acids, and of the liquid fatty

acids, oleic and linolic acids; and the different physical properties

of different samples of lard are due, in the main, to variations in the

proportions of these different constituents. For instance, the firm fat

from the leaf or kidneys of the animal contains fatty acids with a low

percentage (about 15 per cent.) of stearic acid, and a high percentage

(about 58 per cent.) of oleic acid; whereas the fat from the neck and

back, which is very soft, contains fatty acids with about 9 per cent.

of stearic acid, and about 75 per cent. of oleic acid.

=Lard Crystals.=—A curious property of lard, upon which reliance has

often been placed as a test of purity, is that when it is dissolved in

ether and the solution is gradually allowed to evaporate, crystals of

characteristic form are often produced.

The fat crystals from an ordinary soft lard have flat edges and

chisel-shaped ends, whereas the similar crystals from beef fat are

in the form of bunches of needle-shaped crystals. A small proportion

of beef fat added to a soft lard influences the crystallisation

sufficiently to produce bunches of needle-shaped crystals, though

chisel-ended crystals may also be detected.

Unfortunately for the purpose of this test, flare or leaf lard may also

produce crystals which very closely resemble those derived from beef

fat, and this resemblance is rendered closer by re-crystallisation, so

much so that in some cases the two kinds of crystals are practically

indistinguishable.

Hehner and the writer (Mitchell) found that the needle-shaped crystals

contained a higher proportion of stearic acid than the chisel-ended

crystals, and attributed the characteristic differences to this fact.

It has been shown, however, by Kreis and Hafner that the difference is

due to the characteristic flat crystals of lard consisting of a mixed

glyceride heptadecyldistearin, whereas the crystals from beef and

mutton fat consist of another mixed glyceride, palmitodistearin.

According to Dunlop, it is possible, by continued re-crystallisation of

beef fat crystals, to obtain eventually a deposit containing crystals

which are practically indistinguishable from those given by an ordinary

lard.

From all this it will be seen that there is considerable risk of making

a mistake, if judgment of the purity of lard is based solely upon the

form of the crystals, as has sometimes been done. The fact that the

crystals are chisel-shaped may be regarded as presumptive evidence of

the purity of a lard, but the occurrence of bunches of needle-shaped

crystals does not necessarily indicate an addition of beef fat.

=Influence of Food.=—A point of considerable importance to the

manufacturer of lard is that the food given to the animal may have a

pronounced influence upon the composition and chemical reactions of the

lard.

The fat of the wild boar differs from that of the domestic hog in being

of a much more fluid nature. There is also some difference between the

fat of wild and domestic hogs, the former containing a greater amount

of unsaturated glycerides.

The more fluid character of American lards as compared with European

products is to be attributed, in part at all events, to the animals

being fed upon cotton-seed cake.

It has been shown by Dunlop, however (_J. Soc. Chem. Ind._, 1906, xxv.

459), that hogs fed upon cotton-seed cake give lard yielding pronounced

colour reactions for cotton-seed oil, but not, judging by the iodine

value, containing an abnormal amount of fluid fatty acids.

Animals fed upon cocoanut oil cake (copra) also show the influence of

the food in their lard, which, without special knowledge of this fact,

would certainly be condemned as having been adulterated with that

vegetable fat.

This is shown in the following analytical values of lards from

Philippine hogs to which a daily supply of cocoanut oil cake had been

given (Gibbs and Agcaoili, _Philippine J. Science_, 1910, v. 33):—

+---------------------+---------+--------+------+--------+----------+

+---------------------+---------+--------+------+--------+----------+

| Maximum | 46·0 | 199·0 | 52·7 | 53·8 | 43·8 |

| Minimum | 42·5 | 196·0 | 46·7 | 50·0 | 41·6 |

| Mean | 44·7 | 196·9 | 49·4 | 51·7 | 42·7 |

| Maximum | 47·0 | 213·7 | 42·5 | 46·2 | 42·3 |

| Minimum | 44·0 | 204·6 | 32·5 | 36·2 | 39·4 |

| Mean | 45·3 | 208·9 | 37·7 | 41·3 | 40·4 |

+---------------------+---------+--------+------+--------+----------+

=Acidity of Lard.=—In order to obtain a practically neutral product,

the fat intended for lard should be rendered as soon as possible

after the animal has been killed. After standing for some time, the

fat in the adipose tissue gradually undergoes decomposition, with the

liberation of free fatty acids, and the acidity steadily rises. In

refined lard the process of hydrolysis is greatly checked through the

removal of nitrogenous substances, but the development of acidity will

continue when the fat is exposed to the influence of light and air.

As a rule, a freshly prepared lard does not contain more than 0·5

per cent. of free fatty acids (as oleic acid), and frequently the

proportion is very much lower. Thus the acidity of fats from the leaf

and kidneys of six Philippine hogs examined by Gibbs and Agcaoili

(_loc. cit._) ranged from 0·28 to 0·38 per cent. On the other hand, the

intestinal fat contained considerably more free fatty acids (0·86 per

cent.). Samples of American lards examined by Wiley (_loc. cit._) had

an acidity ranging from 0·35 to 1·0 per cent. An acidity in excess of 1

per cent. probably indicates either that the lard was not prepared from

fresh material or that it has been exposed to the air for some time.

=Water.=—Lard should not contain more than a small proportion (0·75 per

cent. at most) of water, and as a rule most commercial samples contain

considerably less than 0·5 per cent.

Polenske (_Arb. a. d. Kaiser. Gesundheitsamte_, 1907, xxv. 505)

found that there was a relationship between the temperature at which

the melted fat became turbid on cooling and the proportion of water

present, and on this fact based a rapid method of estimating the

moisture. Thus the following figures were obtained by Fischer and

Schellens (_Z. Unters. Nahr. Genussm._, 1908, xvi. 161):—

+--------------------------+----+----+----+----+----+----+----+

| Water, per cent. |0·45|0·40|0·35|0·30|0·25|0·20|0·15|

| Turbidity Temperature °C.|95·2|90·8|85·0|75·8|64·6|53·2|41·2|

+--------------------------+----+----+----+----+----+----+----+

In their opinion, based upon the examination of a large number of

German lards, the proportion of water should be less than 0·3 per

cent., corresponding to a turbidity temperature not exceeding 75° C.

Gross adulteration of lard with water is no longer a common practice.

=The Iodine Value.=—Important information as to the purity of lard is

sometimes afforded by a determination of the percentage of iodine with

which it will combine.

As a rule, European lards have iodine values not exceeding 61, and an

iodine value considerably in excess of that figure, say 66, suggests

the addition of cotton-seed oil or of other vegetable oils with high

iodine values.

From what has been stated above, however, it will be seen that

an abnormal iodine value is not in itself sufficient proof of

adulteration, since American lards of genuine character may show that

characteristic.

The differences in this respect between American and German lards are

attributed by Voigtländer (_loc. cit._) to the fact that American lards

contain a large proportion of lard oil of a more unsaturated character.

Thus, while German lard contains only about 50 per cent. of lard oil

with an iodine value of 70-75, American lard may contain about 60 per

cent. of lard oil with an iodine value of 88.

Some of the semi-fluid Russian lards sold in Germany contain as much as

90 per cent. of lard oil.

Of 100 samples of American lard imported into Germany, 88·5 per cent.

had an iodine value between 61 and 66, and 41 per cent. a value

exceeding 64.

The fixing of a standard for the iodine value of lard is unlikely to

result in the sale of a purer product, judging by the experience of

places where such a standard has been fixed. Thus at one time 62 was

fixed as the limit for the iodine value in Bavaria, and the result was

a widespread addition of beef stearin to make the lards answer to this

requirement.

=Lard Oil.=—The fluid portion expressed from lard in the separation of

lard stearin is known as _lard oil_.

It has a soft, pleasant taste, and, being almost free from odour, forms

a good edible oil.

It consists in the main of olein, with a small proportion of glycerides

of solid fatty acids, chiefly palmitic acid. A typical sample will have

values similar to the following:—

+--------+--------------+------+------+--------------+-------------+

+--------+--------------+------+------+--------------+-------------+

| 0·914 | 194 | 97 | 76 | -4° C. to | 35° C. |

| | | | | +10° C. | |

+--------+--------------+------+------+--------------+-------------+

It is thus evident that a large amount of lard oil can be added to

olive oil without making the values of the mixture abnormal.

It also gives a similar product in the elaidin test, and the

phytosterol test (p. 101) is probably the best means of detecting it.

In turn it is liable to be adulterated with cheaper vegetable oils,

such as arachis, cotton-seed, and sesame oils, the presence of each of

which would be shown by their special tests. The oleo-refractometer is

also a means of determining the purity, since the ordinary reading of

lard oil, which ranges from about -1° to +5°, would be increased by

most of the oils employed as adulterants (with the exception of other

animal oils and arachis oil).

CHAPTER VI

MARGARINE AND OTHER BUTTER SUBSTITUTES

Margarine, Oleomargarine, or Artificial Butter—Invention

and Development—Modern Processes and Formulæ—Vegetable

Butter.

It has already been pointed out in Chapter I. how essential in all

except very hot countries is a fair proportion of fat in the human

diet, and, prior to the introduction of artificial butter, this could

only be largely made up among the poorer classes of the community by

the use of “dripping,” the price of genuine butter being prohibitive.

Realising the importance of the subject, the French Government in 1869

offered a prize for the discovery of an artificial substitute for

butter, which should not only be cheaper, but also remain free from

rancidity for a longer period than butter. This led M. Mège-Mouries, a

French chemist, to investigate the whole question of the formation of

fat in milk, and he was successful in securing the prize. Physiological

experiments soon led him to the conclusion that in the series of

transformations by which the butter fat is produced in the animal

economy, the carbohydrate matter consumed by the animal is first

converted into fat, and this in turn, after being deprived of much of

the stearin it contains, by respiratory combustion, is changed by the

digestive action of pepsin into butter fat, and a method was devised

for effecting this latter process artificially.

The original plan adopted by M. Mège-Mouries was to take 1000 kilos

of fresh beef fat, preferably from the kidney or intestines, and

after thoroughly comminuting it and freeing it from tissue, to warm

it at 45° C. with 300 kilos of water, 1 kilo of carbonate of soda,

and two sheep’s or pigs’ stomachs for two hours, when, under the

action of the pepsin, the fat separated completely from any remaining

tissue, and came to the surface as a homogeneous fluid. This was then

decanted into a second vessel warmed to 45° C., and washed with a 2

per cent. solution of common salt, which prevented any fermentation.

After allowing it to stand, a limpid yellow fat separated, having a

butter-like odour, and on cooling to 20-25° C., this crystallised to a

semi-solid mass, with a granular structure which, when the fat was cut

in thicknesses of half an inch, wrapped in linen cloths, and subjected

to a moderate hydraulic pressure between hot plates, at a temperature

of 25° C., allowed 50 to 60 per cent. of a soft fat, comparatively free

from stearin, to be expressed.

This fluid fat, or “oleomargarine,” as it was called, solidified on

cooling, and constitutes what was originally sold in Paris under the

name of “Margarine.”

This soft fat was next converted by Mège-Mouries into a product more

closely resembling natural butter by churning it for two hours with 10

per cent. of cow’s milk, and water in which was macerated 0·4 per cent.

of cow’s udder, complete emulsification being effected by the action of

the pepsin and the churning. After washing with cold water, salting,

colouring with annatto, and finishing off as with ordinary butter, a

very good imitation of the natural article was obtained.

According to Boudet, this artificial butter has a melting-point of 17

to 20° C., contains about 12·5 per cent. of water, and, in the dry

state, 1·20 per cent. of insoluble casein, and is less liable to become

rancid than natural tallow.

Factories were soon erected at Poissy and at Liesing, near Vienna, to

work the process, which was patented by Hippolyte Mège-Mouries, in

England, in 1873. The English patent claimed a process for preparing

artificial butter by mixing the oleomargarine with water containing

sodium bicarbonate, casein, and mammary tissue. The sale of artificial

butter was authorised by the Council of Hygiene of Paris in 1872, the

use of the name “butter” to describe it being prohibited.

The name “margarine” was first applied by Chevreul to what was at

that time considered to be a definite single compound of margaric

acid with glycerin, and found in human fat and olive oil. Subsequent

research by Heinz has shown, however, that so-called margaric acid

is in reality a mixture of stearic and palmitic acids, and the term

“margarine” does not therefore represent any definite chemical body.

The name “oleomargarine” was introduced to signify what was believed

to be a mixture of olein and margarine from which the stearin had

been separated. Part of the “margarine” is now known to consist of

stearin and palmitin, so that the oleomargarine still contains these

two glycerides, though to a much smaller extent than in the original

beef or mutton fat. The softer fat, from which the stearin has been

removed, is known in America as “oleo oil,” the artificial butter made

therefrom being termed “oleomargarine.” In this country it was decreed

by the Margarine Act of 1887 that all artificial butter should be

sold under the name of “margarine,” and this has long since become a

well-established, popular name, such terms as “butterine,” and “Dutch

butter,” which had gradually come into use, being declared illegal by

this Act.

The successful working of the Mège-Mouries process quickly led a number

of other investigators to take up the subject of the production of

artificial butter, and the next few years following were prolific in

patents for the purpose.

Among many others, Lake, in 1871, patented the admixture of cotton-seed

oil; E. G. Brewer, in 1874, the churning of treated tallow with 3 to 4

per cent. of sour milk and 2 per cent. of oil; and Pitt, in 1877, the

addition of arachis oil; Mège the same year obtaining a further patent

for the use of an artificial gastric juice, consisting of hydrochloric

acid and acid phosphate of lime, to help in the artificial digestion of

the fat.

In spite of these, the method of margarine manufacture does not appear

to have undergone much change, and is to-day in most respects closely

similar to that originally proposed by Mège, with the exception that

the artificial digestion of the fat is now dispensed with, and a

certain proportion of vegetable oils is generally added.

In this country the oleomargarine, or basis of artificial butter,

consists usually of the softer portion of tallow or “premier jus,” but

in America a very large part of this, which after further treatment

is there known as “oleo oil,” is replaced by “neutral lard” obtained

from the perfectly fresh leaf, or kidney and bowel, fat of the pig. The

preparation of the “neutral lard” is almost identical with that adopted

for tallow, and as the latter is invariably employed in this country,

the modern preparation of margarine with this as a basis will now be

described.

=Modern Process.=—The carefully selected caul fat of freshly slain oxen

is first washed in a vat with warm water to remove blood and tissue,

then hardened by chilling with ice water, and thoroughly comminuted by

passage through rollers or cutting machines. It is next transferred

to tin-lined and steam-jacketed vessels, in which it is raised to a

temperature of about 40 to 45° C., when the softer portions of the

tallow melt and rise to the surface, the separation being facilitated

by sprinkling salt over the surface.

This clear oil, which is known as “premier jus,” is then siphoned off

into a second series of steam-jacketed vessels, in which it is raised

to about 45° C., after which more salt is added, and a further settling

takes place. The clear, super-natant oil is next transferred to shallow

wooden vats, in which it is allowed to stand for three to five days

at a temperature not exceeding 20° C., in order to crystallise out

the stearin, after which it is thoroughly mixed, wrapped in canvas

cloths, and subjected to pressure, whereby the soft “oleo oil,” or

oleomargarine, is separated from the harder stearin or oleo-stearin,

which is used in the manufacture of lard substitutes, or sometimes in

margarine in place of part of the oleomargarine, when a large quantity

of vegetable oils has been employed.

The oleo oil is then removed to churns, in which it is mixed with

“neutral lard,” cotton-seed oil, olive oil, sesame oil, maize oil, or

other vegetable oil, and milk (fresh or sour) or cream, or sometimes

water, a certain proportion of butter being frequently added to impart

a better flavour to the margarine.

The churning is frequently carried out in special vessels fitted with

internal agitators, and a novel form of these has been patented by

Schroeder (Eng. Pat. 25,404, 1905), in which the blades rotating at

a high speed gradually convert the ingredients into a cohesive and

homogeneous emulsion, which is forced out at the bottom of the vessel.

After churning until completely emulsified, the mixed fat is drawn off

into tubs containing pounded ice, which cool it rapidly and so prevent

crystallisation. It is then coloured with annatto or other colouring

matter, and after salting if desired, is finished off in the same way

as ordinary butter.

The number of materials available renders a very large variety of

combinations possible, and, naturally, successful formulæ used by

private firms are kept secret. The following formulæ were published,

however, by the United States Census Report for 1900:—

CHEAP GRADE.

Oleo oil 495 parts

Neutral lard 265 ”

Cotton-seed oil 315 ”

Milk 255 ”

Salt 120 ”

Colouring matter 1¼ ”

which is sufficient to produce 1265 to 1300 parts.

MEDIUM HIGH GRADE.

Oleo oil 315 parts

Neutral lard 500 ”

Cotton-seed oil 280 ”

Milk 280 ”

Salt 120 ”

Colouring matter 1½ ”

producing 1050 to 1080 parts.

HIGH GRADE.

Oleo oil 100 parts

Neutral lard 130 ”

Butter 95 ”

Salt 32 ”

Colouring matter ½ ”

producing about 325 parts.

Such a formula as this would not be permissible in this country, where

the maximum addition of butter to margarine is fixed by law at 10 per

cent., and the neutral lard is more usually replaced over here by

oleomargarine or “oleo oil,” a suitable formula being as follows:—

Oleomargarine 230 parts

Cotton-seed oil 40 ”

Olive oil 20 ”

Butter 30 ”

Salt 32 ”

Colouring matter ½ ”

The proportion of cotton-seed oil should not, speaking generally,

exceed more than about 25 per cent., or its characteristic flavour

becomes apparent. Besides cotton-seed and olive oils, arachis, palm

nut, and cocoanut oils now enter frequently into the composition of

margarine, and in Germany the use of sesame oil to the extent of 10 per

cent. has been compulsory since 1897. Palm oil, which imparts a yellow

tint to the margarine, is also occasionally incorporated. This being a

firm fat enables the proportion of animal fat to be reduced.

The colouring matter usually employed is annatto, but turmeric and

saffron are also occasionally used. The use of mineral colours is most

objectionable, and coal tar colouring matters are to be discouraged,

though azo dyes are occasionally met with.

Glycerin is sometimes added to margarine to impart a glossy appearance,

and sugar or glucose to sweeten it or improve its texture, though this

is said to injure its keeping qualities.

Many methods have been devised for causing margarine to froth and

become brown when heated, as does genuine butter. The addition of

a fair proportion of butter will, of course, secure this, but in

the absence of butter it may be accomplished by adding a sufficient

quantity of milk. The introduction of casein, lecithin, or cholesterol

has been suggested for the purpose, and Fendler has patented the

use of 0·5 per cent. of egg yolk, subsequent patentees claiming the

preliminary emulsification of the egg yolk with salt solution, lactic

acid, etc. Mitscherlich has recently patented the addition of meat

extract or yeast.

Though not really necessary in a properly made margarine, various

artificial flavourings are occasionally added, ostensibly to render the

flavour more similar to that of genuine butter, but more probably, in

many cases, to enable a proportion of the margarine to be used in the

adulteration of butter without detection by the usual chemical methods.

Such flavouring materials include butyric acid or other volatile fatty

acid, and certain butyrates, these being dissolved in glycerin or oil,

and added in this way to the margarine. Coumarin is also said to be

used, and H. A. Snelling recently patented the addition of banana fruit

or banana essence.

=Vegetable Butter.=—During the last few years a number of products

have appeared on the market under the names of “Vegetable Butter”

or “Nut Butter.” These consist chiefly of carefully refined and

deodorised cocoanut oil and palm-kernel oil, materials which have

lately been supplemented by the addition of margosa oil, shea butter,

and mowrah-seed oil. Any suitable mixture of these may be churned with

milk, coloured, and salted, and finished off like genuine butter.

=Palm Oil.=—Palm-kernel oil has long been utilised as an edible fat,

but hitherto all attempts to make use of any considerable quantity of

the fat from the pulp of the fruit (palm oil) have proved unsuccessful.

This is not on account of the deep orange colour of the fat, which

could be readily removed by oxidation, but owing to the high proportion

of free fatty acids.

The cause of this drawback has been shown by Fickendey (_Der

Tropenpflanzer_, 1910, xiv. 566) to be due to the presence of an enzyme

in the fresh fruit. For instance, the fat extracted from perfectly

fresh fruit had an acid value of 94·5-116, which became still higher

if the fruit was allowed to stand for twenty-four hours before the

extraction of the fat.

By heating the fruit this enzyme is destroyed, and the fat will then

show a low acid value. Thus in four instances in which this was done

the acid value did not exceed 5·3.

Fickendey concludes from these experiments that it would be quite

possible to put a palm oil of good quality upon the market, provided

that the following conditions were observed:—(1) Expression of fresh,

completely ripe fruit; (2) destruction of the enzyme by boiling; (3)

rapid treatment of the fruit. The last condition is essential, owing to

the readiness with which micro-organisms will decompose the fat in the

heated fruit.

CHAPTER VII

SALAD OILS

Salad Oils—Oils used for Culinary and Confectionery Purposes— Chocolate

Fats.

=Olive Oil.=—No oil is so extensively used in the preparation of salad

dressings as olive oil, and the more closely its characteristics can be

imitated by other salad oils the greater is the demand for the latter.

There are several species of the olive tree, some of which are

successfully cultivated in hot climates, but the oil used in Europe is

mainly derived from different varieties of _Olea europæa_. The fruit

produced by these varies considerably in size and in colour, but the

oils that they yield show a close similarity in chemical and physical

characteristics, though they differ from one another in flavour and in

colour.

Apart from the influence of soil and climate and of the variety of

the olive tree, the flavour of the oil also depends upon the stage of

growth at which the fruit is gathered and upon the method of separating

the oil from the pulp.

Fruit that is picked before it is quite ripe yields an oil with a

somewhat bitter flavour, and therefore in preparing the finest grade

of oil the olives are specially selected and pressed by hand between

cloths. The resulting oil is washed with water to remove impurities,

then decanted from the aqueous layer, and sold under the name of

_virgin oil_.

The bulk of fine commercial olive oil, however, is separated by

expression, the ripe olives being superficially crushed between

mill-stones, and then expressed at a low pressure. The residue left

in the press is broken up, mixed with hot water, and the liquid,

consisting of the mixed oil and water, expelled by stronger pressure,

and allowed to stand for the oil to separate. The flavour and colour of

this oil is inferior to that of the cold-drawn product.

Subsequent grinding of this second residue, followed by another

expression with hot water, yields an additional quantity of oil,

while the amount still present is often extracted by means of carbon

bisulphide or other volatile solvent. The oils finally obtained are

generally utilised as lubricants or in the manufacture of soap.

In most districts care is taken not to crush the olive stones until

after the finest oil has been expressed, although according to

Klein (_Zeit. angew. Chem._, 1898, 847) there is no disadvantage in

expressing the mixed kernel and fruit oil, provided the fruit is

freshly picked. The general opinion of the trade, however, is that the

flavour of the pulp oil is superior to that derived from the mixed pulp

and kernels.

Oils that have been extracted by means of carbon bisulphide are known

as “sulphocarbon” oils, while those which have been separated by means

of petroleum spirit are termed “pyrene” oils.

The oils derived from olives that have been left for some time before

expression are of an inferior kind, and are termed _huiles d’enfer_,

_huiles tournantes_, etc. They contain a large amount of free fatty

acids, and have a sharp, unpleasant flavour which renders them

unsuitable for food.

The finest qualities of oil are derived from the districts round Lucca

and Leghorn, and from Provence. Large quantities of excellent oil

are also exported from Spain, Portugal, Algiers, and Tunis, while

California has now become an important oil-producing country.

The flavour is the chief criterion of the quality of olive oil, and a

trained palate is able to detect slight differences which could not be

recognised by any chemical tests.

The so-called _virgin oil_ is pale yellowish-green in colour, and has

but little odour, whereas the lower grades of oil obtained from the

_marc_ left in the press, as described above, vary in colour from

greenish-yellow to light brown, and have a perceptible odour and a

somewhat bitter flavour.

Even the purest olive oil will yield a deposit of “stearin” when

exposed to a low temperature, but the amount varies with the kind

of olive which yielded the oil. Thus it is particularly abundant in

the case of Tunisian and Algerian oils, and it is therefore usual to

remove a portion of this solid fat before putting the oil upon the

market, under the name of “demargarinated” oil. The amount of “stearin”

thus removed depends upon the temperature to which the oil is chilled

before being pressed in a filter-press. Oils thus treated are sometimes

described as “winter oils” (see Chapter III.).

Olive oil consists chiefly of olein, with smaller quantities of the

glycerides of linolic acid and of various solid fatty acids (mainly

palmitic acid) which form the insoluble deposit—the so-called “stearin.”

It belongs to the class of non-drying oils, and hence does not form a

skin on its surface when exposed to the air, and when spread in a thin

film upon glass takes many days to dry up. In this respect it differs

from the semi-drying oils—cotton-seed, sesame, and maize oils—which

are frequently sold as salad oils, sometimes under descriptions that

suggest that they are olive oil.

The chief analytical characteristics of a typical olive oil are as

follows:—

+--------+----------------+--------+--------+---------------+

+--------+----------------+--------+--------+---------------+

| 0·918 | 191 | 82 | 95 | 24° C. |

+--------+----------------+--------+--------+---------------+

Olive oil is very frequently adulterated, the principal substances used

for the purpose being cotton-seed, sesame, maize, and lard oils. The

vegetable oils may be detected by their general analytical values, and

the two first by the characteristic colour reaction (see Chapter VIII.

pp. 105 and 107), whilst lard oil may be detected by the cholesterol

test (p. 101).

=Arachis Oil.=—The chief centre of the arachis oil industry is the

South of France, and at Marseilles in particular enormous quantities of

the nuts are expressed.

The oil obtained by the first expression in the cold is a pale yellow

fluid which is extensively used as a salad oil. A large proportion of

the oil obtained on subsequent expression is sold as a lower grade

of salad oil, while the remainder, and also the oil obtained by hot

pressure, is manufactured into soap. The total yield of oil is from 45

to 50 per cent.

As a rule, the salad oils (which are sometimes sold as “nut salad oil”)

have a distinct odour and flavour of the nut, but in the very finest

grades, which also have but little colour, this flavour is hardly

noticeable in the case of the freshly prepared product. Arachis oil

becomes turbid at a much higher temperature and throws down a more

abundant deposit of “stearin” than olive oil, and this has greatly

interfered with its popularity as a salad oil in this country. The

solidification point is usually about +2 to +3° C. Chemically it

consists of the glycerides of hypogæic, oleic, linolic, palmitic,

stearic, arachidic, and lignoceric acids. The most characteristic

constituents are the two last fatty acids (amounting to about 5

per cent.). They are only slightly soluble in cold alcohol, and on

this property are based several methods of separating them and of

calculating from the result the proportion of arachis oil in, for

example, an adulterated olive oil.

The physical and chemical constants of arachis oil vary considerably,

as is shown in the following figures recorded by Sadtler and by

Crossley and Le Sueur for oils of different origin:—

LEGEND:

(A) = Saponification Value.

(B) = Reichert-Meissl Value.

+----------+---------+-------+--------+-------+-----------+--------+

| Oil. | at | (A) | Iodine | (B) | (as | Fatty |

| | | | | | per cent. | °C. |

+----------+---------+-------+--------+-------+-----------+--------+

|Virginian | 0·917 | 192·5 | 91·7 | 0·48 | 0·55 | 29 |

|Spanish | 0·9175 | 190·7 | 94·2 | 1·60 | 0·79 | 34 |

|African | 0·911 | 194·0 | 85·6 | | 0·62 | 30 |

|Indian | 0·9223 | 190·1 | 98·5 | Nil. | 1·45 | |

+----------+---------+-------+--------+-------+-----------+--------+

The highest figures recorded for the iodine value of arachis oil are

101-105 (Oliveri), whereas the lowest values fall well within the

limits of those of olive oil.

Arachis oil is sometimes adulterated with cheaper oils, and notably

with sesame and cotton-seed oils. The determination of the analytical

values and the characteristic colour reactions will probably afford

information in such cases, while at the same time there would be a

decrease in the amount of arachidic acid that could be separated.

The methods of separating and determining this acid are described in

Chapter VIII. p. 108.

=Sesame Oil.=—This oil also goes by the name of _teel oil_ and

_gingelly oil_, and in commerce is sometimes described as _French salad

oil_.

It belongs to the same class of oils (_semi-drying_) as cotton-seed

oil, which it also resembles in its chemical composition.

It contains the glycerides of oleic, linolic, palmitic, and stearic

acid. The solid fatty acids amount to about 14 per cent. of the total

fatty acids, while, according to Farnsteiner, the linolic acid is about

12 per cent.

The unsaponifiable matter contains phytosterol, a body termed

_sesamin_, and a compound of the nature of a phenol, termed _sesamol_.

It is to the presence of this substance that the characteristic

furfural reaction (see Baudouin’s test, p. 105) is due.

This active constituent may be removed from sesame oil by treatment

with animal charcoal, and the oil may also be rendered inert by

prolonged heating over boiling water.

Sesame oil has a pale yellow colour and a pleasant odour of the grain.

It solidifies at a lower temperature (5° C.) than cotton-seed oil, and

does not yield the large proportion of “stearin” given by the latter.

In the elaidin test it gives a reddish-brown partially solid mass of

about the same consistency as the elaidin of cotton-seed oil.

Its iodine value (usually about 106) is somewhat lower than that of

cotton-seed oil, except in the case of the oil from Russian seed, which

has an iodine value of 114-115.

As is mentioned elsewhere, the addition of sesame oil to margarine

is compulsory in Germany, Austria, and Belgium, so that the product

possesses a “latent colour” which may be developed by the use of the

Baudouin reagent.

In addition to its use as a salad oil, and in pharmaceutical

preparations, sesame oil is employed as an adulterant of olive and

almond oils; while, in turn, it is liable to be adulterated with

arachis oil, cotton-seed oil, poppy oil, and rape oil.

The presence of the first may be detected by an estimation of the

arachidic acid (p. 108), while Halphen’s test will show the presence of

cotton-seed oil.

The other oils are detected by the general physical and chemical

characteristics, and, in the case of rape oil, by the characteristics

of its principal fatty acid, erucic acid.

=Cotton-Seed Oil.=—This oil, as has been already mentioned (p. 16),

is expressed in enormous quantities in the United States, while there

is a steadily increasing production in Egypt and India. In practice,

a ton of cotton seed yields about 2½ cwt. of crude oil, which is then

separated into “summer oil” and “foots” by refining (p. 23).

The bulk of the cotton-seed oil used for food in this country is

derived from Egyptian seed, for the Indian oil is considered to have an

unpleasant flavour.

Experiments made by Hooper, however, upon oils derived from American

seed grown in India (_Ann. Report, Indian Museum_, 1910, 26), show that

the fault lies with the method of screening the seed and the process of

refining the oil.

He finds that by treating Indian oils with the amount of alkali

corresponding to the acidity and giving a subsequent thorough washing

with water, the whole of the colouring matter, the so-called “bloom,”

and the acid taste are removed, and that the product has the light

colour and bland flavour of refined Egyptian oil.

Thus by removing all dirt from the seed and delivering the seed in

sound condition, and washing the oil to a sufficient extent after

the refining with alkali, there appears to be no reason why oils

from Indian seed should be in any respect inferior to Egyptian oils.

Hooper’s experiments also indicate that as much “stearin” could be

separated from Indian oils as from American or Egyptian oils.

Cotton-seed oil consists chiefly of the glycerides of oleic and

linolic acids, the latter, as is indicated by the iodine value, being

present in greater proportion than in olive oil, and amounting to

about 17 or 18 per cent. of the total fatty acids. The glycerides of

solid fatty acids which are present in solution, and separate out as

“cotton-stearin” on chilling the oil, consist principally of those

of palmitic acid with a small proportion of stearic acid (Hehner and

Mitchell).

Owing to the presence of the large amount of linolic acid, cotton-seed

oil belongs to the class of oils known as “semi-drying” oils, _i.e._

oils which thicken on exposure to the air, but, unlike the drying oils,

do not form a dry film until after the lapse of a long time.

When exposed to a temperature of about 10° to 14° C., cotton-seed oil

yields a deposit of the so-called “cotton-stearin” (_q.v._), while

the entire oil becomes solid at about the freezing-point of water.

The stearin, which is separated by filtration (p. 25), is a useful

by-product, which is utilised in the preparation of margarine. The

oil from which the “stearin” has been separated goes by the name of

“winter” cotton-seed oil.

Oils which have been refined by treatment with alkali and separation of

“stearin” have a mild taste and are practically devoid of free acids.

They are widely employed both as salad oils and as substitutes for lard

in cooking, but the bulk of the American oil is made up into margarine

or used in the manufacture of soap.

Cotton-seed oil is a common adulterant of olive oil, and, owing to

its forming a frequent ingredient of margarine, may find its way into

butter.

In addition to the colour reactions, described on p. 107, it may be

identified by the relatively high melting-point of its solid fatty

acids (32° to 38° C.), and by its iodine value (112-115).

In the elaidin test (p. 107) it yields a butter-like mass of an orange

colour, very different from the hard white elaidin produced by olive

oil.

Cotton-seed oil contains about 1 per cent. of unsaponifiable matter

consisting chiefly of phytosterol. The presence of cotton-seed oil in

animal oils and fats may thus be confirmed by the phytosteryl acetate

test (p. 101).

=Sunflower Oil.=—Enormous quantities of sunflower seeds are cultivated

in Russia for the production of an edible oil, and most of the oil

mills in that country are engaged in the industry.

The method of expression is similar to that used in this country for

linseed. The seeds are first “screened” from dirt, particles of stalk,

etc., and are then steamed and crushed to a paste, which is wrapped in

hair-cloths and expressed in a hydraulic press. Expression by hand is

still employed in some of the smaller mills.

When freshly obtained from clean seed, sunflower oil is a pale yellow

fluid with a pleasant odour and flavour, but the second (hot) pressings

are much darker in colour, and are used for illuminating purposes and

in the manufacture of varnish.

Sunflower oil has good drying properties, though these are less

pronounced than in the case of poppy or linseed oil. It consists of the

glycerides of oleic, linolic, and palmitic acids, and probably contains

a small amount of linolenic acid.

Its iodine value (about 130) is considerably higher than that of

cotton-seed oil.

When used as a salad oil it has the advantage of keeping fluid to a

very low temperature, but its drying capacity, which causes a film to

form upon the surface when exposed to the air, is a drawback from

which olive and similar non-drying oils are free.

Sunflower oil is occasionally employed as an adulterant of olive

oil. It would be detected by the increase in the iodine value, and,

according to Jean, by its having a slight reducing action upon silver

nitrate in Bechi’s test (_q.v._).

=Poppy Oil.=—The oil expressed from the seeds of the poppy (_Papaver

somniferum_), which is cultivated in Egypt and Asia Minor, has a mild,

bland taste, and is sometimes used as an edible oil.

Its chief use, however, is as a drying oil for paints, for which its

good drying capacity and its light colour make it particularly suitable.

It consists of the glycerides of oleic, linolic, and linolenic acids,

with a small proportion of those of solid fatty acids, including

stearic and palmitic acids.

It bears considerable resemblance to sunflower oil in its chemical and

physical characteristics, as is shown by the following typical values:—

+--------+----------------+--------+--------+----------------+

+--------+----------------+--------+--------+----------------+

| 0·926 | 194 | 140 | 95·4 | -15° to |

| | | | | -20° C. |

+--------+----------------+--------+--------+----------------+

If added in any considerable quantity to olive oil there would be an

increase in the sp. gr. and iodine value of the latter.

=Maize Oil.=—This oil, which is also known as _corn oil_, is obtained

from the germs of the maize or Indian corn (_Zea mais_), and is used to

a limited extent as an edible oil.

It has a pale yellow colour, and a fragrant odour recalling that of the

fresh grain.

It resembles cotton-seed oil in its composition, and contains the

glycerides of oleic, linolic, and palmitic acids, together with an

appreciable quantity of those of volatile fatty acids, as is indicated

by its relatively high Reichert-Meissl value (4 to 4·5).

Like cotton-seed oil it belongs to the class of semi-drying oils,

slowly forming a dry skin when exposed to the air in a thin film.

The following values have been recorded:—

+--------+----------------+--------+--------+---------------+

+--------+----------------+--------+--------+---------------+

| 0·9245 | 190 | 122 | 93·6 | 17°-20° C. |

+--------+----------------+--------+--------+---------------+

The presence of cotton-seed oil, which is sometimes used to adulterate

maize oil, would be shown by the characteristic colour reactions (p.

107). For the detection of maize oil in lard or in butter reliance

would have to be placed upon the general analytical values and upon the

results of the phytosteryl acetate test.

CHOCOLATE FATS

=Cacao Butter.=—In the manufacture of cocoa and chocolate a large

proportion of the fat contained in the cocoa-bean is expressed, and

forms a valuable by-product.

This fat, which is usually termed cacao butter, comes into the market

in moulded slabs, weighing several pounds each.

It is a hard substance of a yellowish colour, having an aroma of cocoa,

and, when broken, shows signs of crystalline structure.

Its flavour and high melting-point render it particularly suitable for

the “cream” of chocolate creams, and large quantities of it are used

for this purpose.

The chemical composition of cacao butter resembles that of other hard

fats, the differences being due to a different proportion of the

various glycerides.

It contains stearic, palmitic, lauric, and oleic acids, while

arachidic, and a fatty acid termed theobromic acid, are also said to

have been identified, though the presence of either is doubtful.

The hardness and high melting-point of the fat are due to the large

proportion (about 40 per cent.) of stearic acid it contains.

The melting-point of the commercial product ranges from about 27° to

34° C.

The relatively low iodine value (usually between 32 and 36) indicates

the presence of a much smaller amount of liquid fatty acids than of

solid fatty acids, the former, according to Farnsteiner, consisting of

oleic acid, and constituting 31 per cent. of the total fatty acids.

It has frequently been stated that cacao butter is not liable to become

rancid. This, however, is not the case, for the fat, like other fats,

does gradually decompose on exposure to light and air, though owing to

its consistency and the low proportion of glycerides of liquid fatty

acids present the process is not rapid, as in the case, for example, of

cocoanut oil.

Cacao butter is frequently adulterated, the principal substances liable

to be found being stearic acid, cocoanut oil, paraffin wax, beeswax,

and various vegetable oils.

Cacao butter fetches too high a price to be used in the lowest grade of

chocolate creams, and various substitutes are now sold.

=Cocoanut and Palm-Kernel Oil Stearins.=—Among the most common of

these cheaper products are the “stearins,” obtained by expression

from cocoanut oil and palm-kernel oil, both of which in their original

condition are too soft, and melt at too low a temperature to be

suitable for this purpose.

In preparing more solid fats these oils are melted and refined, then

chilled down, and subjected to pressure in the cold in a hydraulic

press. A fractionation is thus effected, the expressed portion, known

as cocoanut or palm-nut olein, being much more fluid than the stearin

left in the press, while the latter is more consistent than the

original fat.

Thus while the melting-point of cocoanut oil is usually about 23° C.,

that of the separate is about 30° C.

The following results were obtained by Sachs (_Chem. Rev. Fett- u.

Harz.-Ind._, 1908, xv. 30) in the examination of commercial samples of

these stearins:—

LEGEND:

(A) = Saponification Value.

(B) = Reichert-Meissl Value.

+----------------+--------------+-------+---+-----+------+---------+

| |Melting-point,| at |(A)| (B) |Iodine| (C) |

| | °C. |100° C.| | |Value.| |

+----------------+--------------+-------+---+-----+------+---------+

| stearin |29·3 to 29·5 |0·8700 |252| 3·4 |4·0 to| 28·1 |

| | | | | | 4·5 | |

|Palm-nut stearin|31·5 to 32 |0·8700 |242| 2·2 | 8 |28·5-29·5|

+----------------+--------------+-------+---+-----+------+---------+

Frequently these products are rendered still more consistent by the

addition of a small proportion of an animal stearin or some vegetable

fat of higher melting-point, such as Japan wax.

Thus a commercial preparation consisting of a mixture of cocoanut

stearin with 25 per cent. of Japan wax, melted at 34° to 35°·5 C.,

or approximately at the same temperature as a good specimen of cacao

butter.

=Other Vegetable Fats.=—Of late years various exotic vegetable fats

have been put upon the market as chocolate fats either in their pure

state or in admixture with cocoanut or palm-nut stearins. These fats

include dika fat, tankawang fat (Borneo tallow) and Illipé fat.

_Dika fat_, which is obtained from the seed kernels of _Mangifera

gabonensis_ and other members of the same family, growing on the West

Coast of Africa, is a hard fat, melting at about 39° C. (or higher than

cacao butter), and having an iodine value (5) about the same as that of

cocoanut oil.

_Borneo tallow_ (_tankawang fat_) derived from the seed kernels of

_Shorea aptera_ and other members of the _Dipterocarpi_. The native

method of separating the fat is to suspend the kernels in baskets above

boiling water, and when soft, to express them in primitive presses.

According to Sachs (_loc. cit._), Borneo tallow melts at 37°·5 C., and

has an iodine value of 30-31.

_Illipé butter_ (_Mahua butter_), which is derived from the seeds of

_Bassia latifolia_, is a yellow fat, large quantities of which are

eaten in India.

Nine samples of the Indian product examined by Crossley and Le Sueur

had melting-points ranging from 23° to 29° C., and iodine values of

58·4 to 67·8. The relatively low melting-point appears to depend upon

the large proportion of glycerides of liquid fatty acids present, and

this fat would probably yield a hard stearin on expression.

Other fats that might be used for this purpose, if they could be

obtained in sufficient quantity, are shea butter, from the seeds of

_Bassia Parkii_ (melting at about 25° C.); Mafura tallow, melting at

35° to 42° C.; Mkani fat, melting at about 40° C.; and Malabar or Piney

tallow, produced by the East Indian tree, _Vateria indica_ (melting at

about 37° C.).

Sachs (_loc. cit._) states that favourite substitutes for cacao butter

consist of a mixture of two-thirds of palm-nut stearin with one-third

of cocoanut stearin, and of a mixture of 40 per cent. of Borneo tallow

with 60 per cent. of cocoanut stearin.

CHAPTER VIII

ANALYSIS OF RAW MATERIALS AND FINISHED PRODUCTS

General Methods of Analysis of Fats and Oils—Special

Tests for Individual Oils—Analysis of Butter,

Margarine, Lard, Cheese, Chocolate.

The adulteration of fats and oils becomes year by year more scientific,

the latest developments of chemical research being prostituted to the

purpose of enabling sophisticated articles to elude the vigilance of

the public analyst, whose duty it is to detect such adulteration. A

striking instance of this is furnished by the methods of adulterating

butter described in Chapter IV.

As was there mentioned, a method for the examination of pure butter,

formulated by Reichert in 1879 and subsequently slightly modified by

Meissl and Wollny, was based on the presence of volatile fatty acids,

such as butyric acid, in butter. Butter substitutes, as usually made,

do not contain these volatile fatty acids, at any rate in appreciable

quantity, except when cocoanut oil has been added, and this, therefore,

afforded a means of detecting the presence of artificial in genuine

butter. It has been found, however, that some manufacturers of butter

substitutes, especially on the Continent, have actually added these

volatile fatty acids, ostensibly to improve their flavour, but there

can be little doubt with the real object of enabling the artificial

product to be sold as genuine butter.

It is unfortunately the case that the unscrupulous manufacturer is

generally slightly in advance of the examining authority, and as fast

as the latter detects one form of adulteration, and devises means for

its ready determination, some new form of fraud is invented to take its

place.

As a result of this competition between expert adulterator and public

analyst, the methods for the examination of edible fats are constantly

being improved and increased, and some extremely fantastic and

far-fetched tests have been suggested. In the following pages, however,

only those most usually adopted in a works’ or commercial laboratory

are described.

GENERAL METHODS OF EXAMINATION OF FATS AND OILS

=Raw Materials.=—The appearance, colour, and odour of the sample should

be observed, and any characteristic feature recorded. The taste is

also frequently of value in judging the purity of a fat or oil, but

deductions from this can only be made after considerable experience.

The following physical and chemical data may be determined:—

=Specific Gravity.=—In the case of oils liquid at ordinary

temperatures, this is usually taken at 15° C., the weight of a given

volume of the oil being compared with that of the same volume of water,

at 15° C., the symbol used to denote this being

15°

“_d_ ———— ”.

15°

If a sufficient quantity of the oil is available a Westphal balance or

a hydrometer may be employed for the purpose; if only a small quantity

can be obtained, a specific gravity bottle or Sprengel or Nicol

pycnometer should be used. This latter method is to be preferred where

great accuracy is desirable. The specific gravity bottle or pycnometer

must be first calibrated by filling it up to the mark with distilled

water at 15° C., and weighing it.

The specific gravity of solid fats is taken at some higher temperature

at which they are fluid, preferably at the temperature of a boiling

water-bath, which will generally be found to be about 99° C. This is

compared with the weight of a similar volume of water at 15° C., and is

represented by

99°

“_d_ ———— ”.

15°

The specific gravity of oils and fats is liable to increase with age,

and also varies with the method of treatment during refining.

The specific gravity of butter fat is best taken at a temperature of

35° C., for reasons which are dealt with under the heading of “Butter,”

in Chapter IV.

=Free Fatty Acids.=—These are determined by warming on the water-bath

for a few minutes a weighed quantity (2 to 10 grms. according to the

degree of acidity of the fat) of the fat or oil, with 25 c.c. of

purified methylated alcohol, which has been neutralised immediately

prior to use, with N/10 potassium hydroxide solution, and after adding

phenol-phthalein solution, slowly running in from a burette N/2 or

N/10 alcoholic potassium hydroxide solution until a faint permanent

pink colour is produced. Each c.c. of N/2 or N/10 alkali corresponds

to 0·141 or 0·0282 grm. respectively of free fatty acids, expressed as

oleic acid, and from this the percentage of acidity is calculated.

The free acidity is frequently expressed as the _acid value_, which

represents the number of milligrams of potassium hydroxide, KOH,

required to neutralise the acidity in 1 grm. of oil or fat.

_Example._—If 6·656 grms. fat required 1·5 c.c. N/10 alcoholic

potassium hydroxide solution to neutralise it, then

1·5 × 0·0282 × 100

—————————————————— = 0·63 per cent.

6·656

free fatty acids, expressed as oleic acid.

The _acid value_ in this case would be

1·5 × 0·00561 x 1000

———————————————————— = 1·26.

6·656

The maximum permissible limit for free acidity depends on the nature of

the fat or oil. For edible tallows it should not exceed 3 per cent.,

for lard 0·5 per cent., and for cocoanut oil 2 per cent.

=Saponification Value.=—It has been shown in Chapter I, how the various

glycerides contained in fats and oils are split up or saponified by

the action of caustic alkalies, one molecule of a triglyceride such

as stearin requiring three molecules of potassium hydroxide for its

saponification (cf. p. 4).

The composition of the various fats and oils being fairly constant, the

amount of alkali required for the saponification of any given weight is

also nearly constant. Koettstorfer first utilised this fact in 1879 for

the analysis of butter fat, and it has now become the basis of one of

the most important factors in the analysis of nearly all fats and oils,

the amount of any fat which is saponified by 1 grm.-molecule or 56·1

grms. of caustic potash being termed its _saponification equivalent_.

The more usual method of expressing the same thing is the number of

milligrams of potassium hydroxide required to saponify 1 grm. of fat,

which is called the _saponification value_. The difference between the

saponification and acid values is spoken of as the _ester value_.

To convert saponification equivalent into saponification value, it is

merely necessary to divide 56·1 by the saponification equivalent, and

multiply the quotient by 100.

To determine the saponification value, about 2 grms. of the fat or

oil are weighed out into a conical flask of about 200 c.c. capacity,

25 c.c. of _neutral_ methylated spirit added, and 25 c.c. of an

approximately N/2 alcoholic solution of potassium hydroxide run in

from a burette, similar quantities of methylated spirit and alcoholic

potassium hydroxide solution being also placed in another flask to

serve as a blank test. The two flasks are now fitted with reflux

condensers (which may be simply glass tubes, about four feet long and

half an inch in diameter, inserted through a cork), and are placed on a

steam or water-bath. The contents are then boiled until saponification

of the fat is complete, which may take from thirty to sixty minutes,

and is known to be accomplished when all globules of oil disappear. A

few drops of phenol-phthalein solution are now added to each flask,

and N/2 hydrochloric or sulphuric acid carefully run in from a burette

until the pink colour is discharged. The difference in the amount of

acid required by the two flasks indicates the quantity of potassium

hydroxide required to saponify the weight of fat or oil taken.

_Example._—2·1314 grms. fat required 10·7 c.c. N/2 hydrochloric acid to

neutralise unabsorbed alkali.

In the blank test 25 c.c. of approximately N/2 alcoholic potassium

hydroxide solution required 25·6 c.c. of N/2 hydrochloric acid to

neutralise it.

25·6 - 10·7 = 14·9 c.c. ————

alcoholic potassium hydroxide solution required to saponify the fat, and

2·1314 × 1000 × 2

————————————————— = 286·1

14·9

saponification equivalent, and

56·1 × 100

———————————— = 196·1,

286·1

the saponification value.

If the quantity of fat or oil employed for the estimation of acidity is

only about 2 grms., the saponification value may also be determined on

the same quantity. After proceeding as described above for the acidity

estimation, 25 c.c. of approximately N/2 alcoholic potassium hydroxide

solution are added to this, and the process continued as described

above.

=Iodine Absorption.=—This test, devised by Hübl in 1884, and

subsequently modified by Wijs, by Hanus, and by Waller, is based upon

the capacity of unsaturated fatty compounds to absorb iodine, with

formation of addition compounds. The amount of iodine absorbed is

therefore a measure of the unsaturated compounds present in a fat, and

is very fairly constant for any given fat in the fresh condition. The

action of Hübl’s solution is attributed by Ephraim to the presence

of iodine monochloride, but by Wijs to that of hypoiodous acid. The

percentage of iodine absorbed is usually recorded as the _iodine

number_ or _iodine value_.

In Hübl’s method, two solutions are required—(1) containing 25 grms.

iodine in 500 c.c. of absolute alcohol, and (2) containing 30 grms.

mercuric chloride in 500 c.c. of absolute alcohol. These solutions

should be kept separate, and only mixed about twelve to twenty-four

hours before use.

The process is carried out as follows:—Into a tightly fitting stoppered

bottle is introduced 0·2 to 0·6 grm. of the fat, 10 c.c. chloroform

added, and 25 c.c. of the mixed Hübl solution run in from a burette.

The bottle is then firmly stoppered, and allowed to stand in a dark

place for four hours, a similar bottle containing the same quantities

of chloroform and Hübl solution being placed by its side as a blank

experiment.

At the end of four hours, 20 c.c. of a freshly prepared 10 per cent.

potassium iodide solution and 150 c.c. of water are added to each

bottle, and the excess of iodine titrated with recently standardised

N/10 sodium thiosulphate solution, the bottles being vigorously shaken

during the titration, and fresh starch solution used for determining

the final point. The difference in the number of c.c. of N/10 sodium

thiosulphate solution required by the contents of the two bottles is

a measure of the iodine absorbed by the fat. This figure, multiplied

by the iodine equivalent of the sodium thiosulphate solution (found by

titrating it with a known weight of pure resublimed iodine), and by

100, and divided by the weight of fat taken, gives the iodine value of

the fat.

_Example._—0·539 grm. oil taken. Blank bottle, with iodine solution

and chloroform only, required 61·4 c.c. N/10 thiosulphate; bottle

containing oil required 25 c.c. N/10 thiosulphate. The iodine

equivalent of the thiosulphate solution was found to be 1 c.c. = 0·0126

grm. I.

61·4 - 25·0 × ·0126 × 100

Then ——————————————————————————— = 85.1 iodine value.

·539

_Wijs’ Method._—The Hübl method has now to a very large extent been

displaced by the Wijs process, in which the iodine is absorbed by

the fat much more quickly, only about thirty minutes’ contact being

required. The Wijs iodine reagent consists of a solution of iodine

monochloride in glacial acetic acid, and may be prepared by either

weighing out 7·9 grms. of iodine trichloride (which must be done in a

weighing bottle), and 8·7 grms. of iodine, dissolving these separately

in glacial acetic acid, mixing and making up to a litre with glacial

acetic acid, or by dissolving 13 grms. of iodine in a litre of

glacial acetic acid, and passing chlorine into the solution until the

iodine is all converted into the iodine monochloride—a point which

may be determined by the gain in weight, or, with a little practice,

by the change in colour of the solution. The details of the process

are exactly similar to those in the Hübl method, except that it is

preferable to dissolve the fat in carbon tetrachloride instead of in

chloroform.

=Bromine Absorption.=—This is similar in principle to the iodine

absorption, and though numerous processes, both gravimetric and

volumetric, have been proposed for its determination, it has now been

almost entirely superseded by determination of the iodine absorption.

A process devised by McIlhiney (_J. Amer. Chem. Soc._, 1894, 295, and

1899, 1084), however, deserves attention, for it estimates both the

added and the substituted bromine.

The weighed quantity, say 0.5 grms. of the oil or fat, is weighed

out, and dissolved in 10 c.c. of chloroform, and 20 c.c. N/3 solution

of bromine in chloroform added. After two or three minutes 20 to 30

c.c. of a 10 per cent. potassium iodide solution are added, and the

liberated iodine titrated with standard N/10 thiosulphate, the result

giving the bromine forming addition compounds. After this, 5 c.c. of

neutral 2 per cent. potassium iodate solution are introduced, and the

liberated iodine titrated, the result in this case corresponding to the

hydrobromic acid formed by the bromine in producing substituted bodies,

or, in other words, giving the _bromine substitution value_.

=Titre, or Solidifying Point of the Fatty Acids.=—Many methods for

determining the melting and solidifying points of fatty matters have

been proposed, but the _titre test_, due to Dalican, is that which

is now most generally adopted. This consists in determining the

solidifying point of the fatty acids separated from a fat or oil, a

figure which is an important characteristic of most fats, and in the

case of tallows is largely employed as the basis for their commercial

valuation. It is, of course, essential that in the preparation of

artificial butters from a standard formula the firmness of the fats

used should be as nearly as possible constant, and this is best

determined by the titre test.

The test is carried out by first saponifying the fat with alcoholic

sodium hydroxide solution, decomposing the resulting soap with dilute

sulphuric acid, and after washing and drying the liberated fatty

acids, determining their solidifying point. One ounce of the sample

is melted in a shallow porcelain basin on a water-bath, and 30 c.c.

of a 25 per cent. solution of sodium hydroxide added, together with

50 c.c. of redistilled methylated spirit. The contents of the basin

are now evaporated on the water-bath, with constant stirring, until

a pasty mass of soap is formed, and this is redissolved in a further

50 c.c. of redistilled methylated spirit, and again evaporated to

dryness on the water-bath. The solid soap thus obtained is dissolved

in water, sufficient dilute sulphuric acid added to decompose it, and

the whole warmed until the fatty acids melt to a clear oily liquid on

the surface. The water underneath is now siphoned off, more distilled

water added to wash out any remaining trace of mineral acid, and again

siphoned off, this treatment being repeated until the washings are no

longer acid to litmus paper. The melted fatty acids are next poured

on to a dry filter paper, which is inserted in a funnel resting on a

beaker, and the latter is placed either in the water-bath or in an

air-oven at about 100° C. until the clear fatty acids have filtered

through it.

From 10 to 15 grms. of these dry fatty acids are transferred to a wide

test tube, about six inches long and one inch in diameter, which is

inserted through a cork into a flask or wide-mouthed bottle, to protect

the tube from draught. The tube is closed with a loosely fitting

perforated cork, through which passes a short range thermometer (0°

to 60°), accurately graduated in fifths of a degree centigrade, and

having its bulb just immersed in the fatty acids as near the centre as

possible.

The temperature is now raised to a few degrees above the melting-point

of the fatty acids, and allowed to cool down without stirring. As

soon as the fatty acids just begin slowly to solidify, they are

stirred round gently with the thermometer, the temperature on which

will gradually fall till a minimum point is reached. Stirring is now

discontinued, and the rise in temperature, which is usually produced

by the heat given out by the acids in crystallising, is observed. The

maximum temperature attained by the fatty acids during this rise is the

“titre” of the sample.

=Refractive Index.=—The determination of the refractive power of a fat

or oil, or of its fatty acids, is frequently very useful in judging the

purity of a sample, or in drawing conclusions as to the composition of

a mixture of fats.

The refractive index itself may be either directly determined by means

of an Abbé total reflection refractometer, or an Amagat and Jean

oleo-refractometer (_Analyst_, 1890, 87), or, as is more usual in the

case of butter, the refractive power may be read off on an arbitrary

scale by means of a Zeiss butyro-refractometer.

One of the great advantages of this test is the ease and rapidity with

which a number of samples may be examined, while a further advantage of

the Abbé and Zeiss instruments is that only a very small quantity of

the sample—5 or 6 drops—is necessary.

The different forms of apparatus are fully illustrated and described in

the catalogues of most firms supplying chemical apparatus, and it is

therefore unnecessary to give a description here.

Different observers employ various temperatures for determining

refractive indices, but that most usual for oils and fats, with the

exception of butter, is 60° C. The best temperature of observation for

butter is 40° C.

=Unsaponifiable Matter.=—The unsaponifiable matter present in the

ordinary animal and vegetable fats is very small in amount, and the

addition of any paraffin or other hydrocarbon is therefore readily

detected by estimating the unsaponifiable matter. The usual method is

to saponify about 5 grms. of the fat, dissolve the soap in water, and

extract the unsaponified fatty matter with ether. The saponification is

effected by boiling the fat with 50 c.c. of approximately N/2 alcoholic

potassium hydroxide solution under a reflux condenser, with frequent

agitation, for about an hour. The soapy solution is then evaporated to

dryness in a porcelain basin on a steam or water-bath, and the soap

obtained is dissolved in about 200 c.c. of hot water and transferred,

as soon as sufficiently cool, to a 10 oz. separating funnel. To this

is now added 50 c.c. ether, and the whole well shaken, and allowed

to separate. The aqueous soap solution at the bottom is now run into

another similar separator, and the ethereal extract washed with water

to remove any soap dissolved therein. The washings are added to the

aqueous soap solution, which is again extracted with a second 50 c.c.

of ether, separated, the ethereal extract washed with water, and the

extraction repeated a third time. The three washed ethereal extracts

are then transferred to a tared flask, the ether distilled off in a

water-bath, and the residue dried in the oven at 100° C. till constant

in weight. This residue is the unsaponifiable matter in the weight of

fat taken, whence the percentage may be calculated.

Difficulty often occurs during this process through the formation of

an emulsion between the ethereal and the aqueous solutions, which

prevents a sharp separation of the two layers. To overcome this,

various expedients are recommended, such as the addition of a few c.c.

of alcohol or glycerin or of more ether or water, careful warming, or

gentle rotation.

The unsaponifiable matter may consist of cholesterol, a constituent of

many animal fats, of phytosterol, a substance similar to cholesterol

found in vegetable fats, of solid alcohols, such as cetyl and ceryl

alcohols, present in spermaceti and Chinese wax, or of hydrocarbons,

which do not occur naturally in either animal or vegetable fats, but

are occasionally added as adulterants.

To examine the unsaponifiable matter for cholesterol and phytosterol

a small quantity is dissolved in acetic anhydride, and one drop of

the solution added to one drop of 50 per cent. sulphuric acid on a

white porcelain tile, when, if either is present, a blood red to

violet coloration is produced. They may be distinguished from each

other by their crystalline form, cholesterol crystallising in laminæ,

phytosterol in needle-shaped tufts; or by the melting-points of their

acetates, cholesteryl acetate melting at 114°·3-114°·8, and phytosteryl

acetate at 125°·6-137° C.

The fact that the unsaponifiable matter of animal fats contains

cholesterol, while that of vegetable oils and fats contains

phytosterol, has been made the basis of a test for detecting the

presence of vegetable oils and fats in butter or lard. This test,

which was first proposed by Bömer (_Zeit. Untersuch. Nahr. Genussm._,

1898, 81), consists in saponifying the fat with alcoholic potash,

and extracting the unsaponifiable matter with ether, which is then

distilled off, and the residue recrystallised from alcohol. The

process has been subsequently improved by converting the cholesterol

or phytosterol into the acetic esters by heating it with acetic

anhydride, and determining the melting-point of the resulting ester.

As mentioned above, that of cholesterol melts at about 114° C., that

of phytosterol at 125°·6-137° C., and, according to Bömer, an acetate

melting at 117°-118° C. corresponds to an addition of 1 to 2 per cent.

of vegetable oil; at 120°-121° C., to an addition of 2 to 3 per cent.

of vegetable oil; and at 123°-125° C., to an addition of 3 to 4 per

cent. of vegetable oil.

The following method for carrying out this test, which is known as the

_phytosteryl acetate test_, is described by Revis and Bolton (Allen’s

_Commercial Organic Analysis_, ii. p. 301).

Fifty grms. of the clear fat are boiled with 75 c.c. of 95 per cent,

alcohol, cooled, and the alcohol poured off, a second extraction being

made with a further 75 c.c. of alcohol. These combined extracts, which

will contain the greater part of the cholesterol and phytosterol

and some fat, are transferred to a porcelain basin, and an excess

of solid sodium hydroxide added, the mixture being then evaporated,

with gentle stirring. After most of the alcohol has evaporated, more

than sufficient sodium bicarbonate is added to convert the excess of

sodium hydroxide into sodium carbonate, then some sand, and the whole

evaporated to dryness, ground up in the dish, and extracted with light

petroleum spirit. The residue from the ether is heated with 5 c.c. of

(approximately) N/2 alcoholic sodium hydroxide solution, and again

evaporated to dryness, with sand. A fresh extraction with petroleum

spirit is made, followed by evaporation, and the residue is taken up

with the smallest possible quantity of absolute alcohol. If necessary,

the solution is boiled with animal charcoal and some 95 per cent.

alcohol, filtered and evaporated to dryness. The crystals obtained are

examined microscopically, then converted into their acetate by boiling

with acetic anhydride in a covered watch-glass, evaporating off the

excess of acetic anhydride on the water-bath, and recrystallising them

from absolute alcohol.

Further tests for cholesterol have also been published by Lifschutz

(_Ber. Deut. Chem. Ges._, 1908, 252-5) and Golodetz (_Chem. Zeit._,

1908, 160).

The method of the former depends on the oxidation of cholesterol

to oxycholesterol ester and oxycholesterol. A few mgrms. of the

unsaponifiable matter are dissolved in 2 to 3 c.c. of glacial acetic

acid, a little benzoyl peroxide added, and the solution boiled, after

which four drops of strong sulphuric acid are added. If cholesterol is

present, a violet-blue or green colour is produced, the violet colour

being due to oxycholesterol ester, the green to oxycholesterol.

Golodetz has devised two tests:—(1) the addition to a small quantity of

the unsaponifiable matter of one or two drops of a mixture of 5 parts

of concentrated sulphuric acid with 3 parts of formaldehyde solution,

this reagent turning cholesterol a blackish-brown colour; and (2)

the addition of one drop of 30 per cent. formaldehyde solution to a

solution of the unsaponifiable matter in trichloracetic acid, when, if

cholesterol is present, an intense blue coloration is produced.

Of the less frequently used methods of examination the following may be

mentioned:—

=Valenta’s Acetic Acid Test=, which depends on the solubility of

most oils and fats in hot glacial acetic acid of 1·0562 sp. gr., the

temperature at which a warmed mixture of 3 c.c. melted fat and 3 c.c.

acetic acid becomes turbid on cooling being noted.

The test has been slightly modified by Pearmain and Moor, who use a

short stoppered tube, into which is weighed 2·75 grms. of the fat or

oil, followed by 3 c.c. of acetic acid. The tube is then stoppered and

heated in a water-bath, the temperature being raised until the contents

of the tube become clear on shaking, after which the source of heat is

removed, and the tube allowed to cool down gradually in the centre of

the water-bath until the contents again become slightly turbid. The

temperature at which this takes place is recorded, and is a fairly

definite figure for any given oil. This test is of some value in the

examination of butter for margarine, as is pointed out in Chapter IV.

p. 48; the temperature at which the solution of the latter in acetic

acid becomes turbid being very much higher than that of the former.

The following are the figures obtained by Pearmain and Moor by the

above method:—

° C.

Butter fat 23-38

Margarine 94-97

Lard 97-99

Tallow 96-99

Cotton-seed oil 71-89

Sesame oil 90-97

Olive oil 83-91

The drawback of this test is that slight variations in the strength of

the acetic acid, such as inevitably result from opening the bottle,

cause considerable variations in the temperatures of turbidity. To

obviate this it is advisable to compare the results with those given by

specimens of butter fat of known purity.

=Maumené’s Test=, first proposed in 1852, consists in observing the

rise of temperature which takes place when the fat or oil is mixed with

concentrated sulphuric acid. Various methods of applying the test have

been proposed by different authorities, that suggested by Archbutt

(Allen’s _Commercial Organic Analysis_) being as follows:—Fifty grms.

of oil are weighed into a 200 c.c. beaker, and the latter immersed

in a capacious vessel of water, together with the bottle of strong

sulphuric acid, until they are both at the same temperature, which

should not be far from 20° C. The beaker containing the oil is then

wiped, and placed in a cotton-wool nest previously made for it in a

cardboard drum, or a wider beaker. The immersed thermometer is then

observed, and the temperature recorded. Ten c.c. of the concentrated

sulphuric acid should then be withdrawn from the bottle with a pipette,

and allowed to run into the oil. During the addition of the acid, which

should occupy about one minute, the mixture must be constantly stirred

with the thermometer, and the agitation continued till no further

rise of temperature ensues. This point is readily observed, as the

mercury remains constant for a minute or two, and then begins to fall.

Very different results are obtained according to the strength of acid

employed, the best strength being 97 per cent.

Thomson and Ballantyne (_Journ. Soc. Chem. Ind._, 1891, x. 233)

proposed to determine the “_specific temperature reaction_” of the oil,

this being obtained by noting (1) the rise of temperature produced

when 50 grms. of water are mixed with 10 c.c. of strong sulphuric acid

in the same vessel and under the same conditions as those to be used

for mixing the acid and oil; (2) mixing the oil and acid as described

above, and then multiplying the rise in temperature produced by the

oil-acid mixture by 100, and dividing by the rise in temperature given

by the water-acid mixture. The following figures are given by Thomson

and Ballantyne:—

Temperature.

Oil. Water = 100° C.

Olive 89-95°

Arachis 105-137°

Cotton-seed 163-170°

It has been shown by one of the authors (M.) (_Analyst_, 1901, xxvi.

169), that if the oil be dissolved in an inert solvent, such as

carbon tetrachloride, the rise in temperature on adding sulphuric

acid is usually proportional to the iodine value, i.e. the degree of

unsaturation of the oil.

=Bromine Thermal Value.=—The heat reaction with bromine has been

recommended as a rapid means of ascertaining the degree of unsaturation

of oils and fats by Hehner and Mitchell (_Analyst_, 1895, xx. 146),

a weighed quantity of the sample being dissolved in chloroform or

acetic acid, and the rise in temperature on addition of bromine noted.

The oil, chloroform, and bromine having first been brought to the

same temperature, 1 grm. of oil is dissolved in 10 c.c. chloroform

in a Dewar’s vacuum-jacketed test tube, and 1 c.c. of bromine added

from a special pipette. This consists of a 1 c.c. pipette with a

narrow tube, bent twice at right angles, connected to its top, the

horizontal portion of the tube containing caustic lime kept in position

by asbestos plugs. The mixture is immediately stirred, and the rise

in temperature measured with a thermometer graduated in fifths of a

degree. In the case of most ordinary oils and fats a relationship is

shown to exist between the rise in temperature and the iodine value,

so that this ratio having once been ascertained for the apparatus

employed, the iodine value may be readily calculated from the rise in

temperature observed on adding the bromine.

The preceding methods of examination are more or less generally

applicable to all edible fats and oils, but there are numerous special

tests applicable only to individual oils, of which the following are

the most important. The application of these is also discussed more

generally in the sections dealing with the special oils.

SESAME OIL

_Baudouin’s Test._—This is carried out by dissolving 0·1 grm. of cane

sugar in 10 c.c. hydrochloric acid of sp. gr. 1·2, and adding this to

20 c.c. of the oil under examination, shaking the mixture thoroughly

and allowing it to stand. The presence of as little as 2 per cent. of

sesame oil imparts a crimson red colour to the aqueous liquid. This

reaction is given by even the most rancid oils, though the colour

produced is less intense.

A modification of this, consisting in adding 0·1 c.c. of a 2 per cent.

alcoholic solution of furfural to the hydrochloric acid instead of

the 0·1 grm. sugar, was devised by Villavecchia and Fabris, who found

the reaction to depend upon the formation of furfural; while Wauters

suggested that instead of mixing the reagent with the oil, the latter

should be poured upon the reagent, under which conditions less than 1

per cent. will impart a crimson colour to the surface of contact.

Sprinkmeyer and Wagner (_Zeit. Nahr. Genussm._ 1905, x. 347-353) have

still further increased the delicacy of the test, so that as little

as 0·1 per cent. of sesame oil may be detected. In their process

about 100 grms. of the filtered fat are twice extracted with 20 to 30

c.c. of glacial acetic acid at 60° C. The acid extracts are separated

and evaporated, and the residue tested as described above. In the

case of butter containing colouring matter, which may interfere with

the reaction, the latter may be removed by evaporating the acetic

acid residue with 10 c.c. of alcohol and 5 c.c. of saturated barium

hydroxide solution, and extracting the residue several times with light

petroleum spirit, which is then evaporated, and the final residue

treated with the furfural solution.

_Tocher’s Test._—A freshly made solution of 1 grm. of pyrogallol in 15

c.c. of concentrated hydrochloric acid is shaken up in a separating

funnel with 15 c.c. of the oil, and allowed to separate. The aqueous

liquid is then drawn off, filtered, and boiled for about five minutes,

when, if sesame oil is present, it appears red by transmitted and blue

by reflected light.

OLIVE OIL

An important test for the purity of this oil is based on the elaidin

reaction (p. 11), the degree of hardness of the product obtained by

treatment of the oil with nitrous acid and the time required for its

solidification being observed.

Opinion is divided as to the advisability of having a fixed standard