Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 76

3. (Sulphuric-acid test.)--_a._ Heidenreich was the first person who gave a useful and general application to the reactions which occur when oil of vitriol is mixed with the fatty oils. As soon as these substances are placed together, very intense chemical action commences, the temperature of the mixture rises, and the ma.s.s becomes coloured. These changes are sufficiently varied in the case of the different oils to furnish us with the means of identifying many of them, and of determining their purity.

The method of M. Heidenreich is to lay a plate of white gla.s.s over a sheet of white paper; on the gla.s.s he places 10 or 15 drops of oil, and then adds to it a small drop of concentrated sulphuric acid ('oil of vitriol').

The appearances which follow differ with the character of the fatty oil examined, and whether the acid is allowed to act on the oil undisturbed (without stirring) or the two are stirred together with a gla.s.s rod. In many cases, as with tallow oil, a peculiar odour as well as a change of colour is developed, and a further means of detection supplied. M.

Heidenreich has minutely described these reactions, which, for the most part, closely resemble those given in the table, p. 1129. It is necessary, however, in order to ensure great accuracy, to compare the effect of the reagent on the sample with those which it produces on pure oil of the same kind and character under precisely similar circ.u.mstances.

_b._ M. Penot, who has followed up the researches of M. Heidenreich with considerable success, recommends the employment of 20 drops of oil, instead of only 10 or 15; and the use of a small capsule of white porcelain, instead of a plate of gla.s.s. He also employs a saturated solution of b.i.+.c.hromate of potash in sulphuric acid, which he uses in the same proportion as before; but in this case the oil and the reagent are always stirred together.

The observations of M. Penot have been repeated in many cases by Mr Cooley, and the results, with additions, and rearranged, are given in the table, p. 1129.

"By perusing this table," writes M. Penot, "it will be observed that the same oil does not, under all circ.u.mstances, yield precisely similar results with the same reagent. This depends on the place of growth, the age, and the manner of pressing. If, however, any oil be examined comparatively with a perfectly pure one, the proof of adulteration may be rendered, if not certain, at least probable, by noting the difference.

Thus I obtained, by adding 1 part of either whale-train, or linseed oil, or oleic acid, or 10 parts of rapeseed oil, the following results:--

+-------------------+---------------------------------------------------------+ REAGENTS. +-----------------------------------+---------------------+ NAME OF OIL. Sulphuric Acid. Solution of b.i.+.c.hromate of Potash. +--------------------+--------------+---------------------+ _Not stirred._ _Stirred._ _Stirred._ +-------------------+--------------------+--------------+---------------------+ Rape oil with More red ground Brownish-olive Small reddish lumps whale-train oil than with rape oil coloured on a grey ground. Rape oil with No perceptible Olive coloured Small and more linseed oil difference from numerous red lumps the rape oil on a very dark-green ground. Rape oil with olein No perceptible Greenish brown Small brownish or oleic acid difference from lumps on an the rape oil olive-coloured ground. +-------------------+--------------------+--------------+---------------------+

"The adulteration being ascertained as far as is possible, the oil is then tested by endeavouring to discover the adulterating oil, either by reagents or by its odour when gently heated, as before described. This having been found out, small quant.i.ties of the suspected oil are added to a perfectly pure oil of the kind under examination. Every mixture is then tested by the reagents, until precisely similar results are obtained as those yielded by the oil under examination. Thus, the proportions of the two mixed oils will be discovered by approximation." (M. Penot.) A simpler method of finding the proportions of the so mixed oils is referred to above.

4. (From increase of temperature.) M. Maumene proposed the increase of temperature arising from the admixture of monohydrated sulphuric acid (oil of vitriol, sp. gr. 1845) with the fatty oils as a test of their purity, but a sufficient number of observations have not yet been made to furnish data for a general application of this method. According to MM. Faisst and Knauss, who have re-examined the subject, the following are the results when 15 grammes of oil are mixed with 5 grammes of the acid:

_Rise of Temperature._ Almond oil 725 Olive oil 680 Poppy oil 1270 Rape or colza oil 1000 Linseed oil (with Nordhausen or fuming acid only) 1330

The above method is less liable to error when a larger quant.i.ty of the substances are thrown together.

5. The presence of FISH OIL in the vegetable oils may be readily detected by pa.s.sing a stream of chlorine through them; the pure vegetable oils are not materially altered, but a mixture of the two turns dark brown or black.

6. Mr Coleman states that the presence of mineral oils in animal or vegetable oils can be easily detected by two characteristic tests--(1) the fluorescent properties they impart to all animal or vegetable oils. (2) The strongly marked aromatic burning flavour they communicate to mixtures containing them. The first-mentioned property is brought out by smearing a metallic surface, such as tin plate or steel, with the oil, and then viewing it at different angles in the open air or sunlight. Mr Coleman suggests that, in examining a dark-coloured oil, it may first be necessary to refine the sample by successive treatments with concentrated sulphuric acid and weak soda solution or lime water, so small a quant.i.ty as 2-1/2 per cent. may then be detected by the bluish colour noticed on viewing the oil at certain angles and by tasting it.

The absence of resin oil must also be proved. Nitric acid is said to be a good test, as the colour developed is much greater than in pure oils.

Sometimes it may be detected by the smell. The presence of 10 per cent. of resin or mineral oil in non-drying oils delays their solidification with the nitrate of mercury test.[50]

[Footnote 50: 'Journal of Applied Chemistry,' Dec., 1874.]

7. Miss Kate Crane[51] states that the cohesion figures of oils may be usefully employed as tests of the ident.i.ty and purity of the oils. She says, "A number of experiments on this subject have led her to the conclusion that a little patient practice will teach the eye of the observer in a short time to detect the characteristic differences of the figures. To make these perfect it is necessary to observe the time in forming, for _at different periods_ some varieties form figures very like; but with this precaution each is entirely characteristic.

[Footnote 51: 'American Journal of Pharmacy,' iv, 406.]

"It is essential that the dish used, &c., be perfectly clean, so that when filled with water no dust or lint floats upon the surface, as this materially interferes with the perfect formation of the figure.

"A single drop is let fall from a burette or gla.s.s rod held steadily above the water, upon the centre of the surface. The experiments made with fixed oils are as follows:--_Poppy-seed oil_ spreads instantly to a large figure, retaining an entire outline, and for a few seconds the surface is unbroken, except the bare intimation of a beaded edge.

"In a few moments little holes appear round the edge, and soon the whole surface is broken in like manner; these increase in size very slowly. In fifteen minutes the edge begins to open, forming indentations, which gradually work their way across the figure. As they increase in length these begin to curve, and in three quarters of an hour have doubled themselves two or three times.

"_Cod-liver oil_ spreads in a large film; a little way from the edge a row of small holes appears, and in a minute or two the surface is covered with them; these gradually enlarge, a.s.suming irregular shapes, soon separated by branching lines.

"_Cod-liver oil_ with _lard oil_ spreads very like the former, but in a few moments the edge opens, and the film separates partly across; in a moment one of the projecting points begins to curve itself towards the centre, bending more and more until it forms a coil; meanwhile a few holes have appeared, which spread irregularly, throwing out projecting points.

"_Castor oil_ spreads instantly, the edge remaining entire; openings appear quickly in thirty seconds, and increase gradually, but unevenly, those nearer the edge being larger, and lengthening out irregularly as they spread. The figure lasts some time.

"_Castor_ with a little _lard oil_ makes a smaller figure, and not nearly so much broken; in five minutes the holes open into each other, and the figure breaks up from the edge.

"A mixture of _castor_ and _poppy-seed oils_ spreads to form a lacework border, but smooths out to an entire edge soon, and within a few seconds openings appear. The figure, in size and general appearance, is more like castor oil alone, but the holes spread less uniformly in a given time, a few being larger, but the greater portion much smaller. In fifteen minutes there is a general tendency to break up.

"_Castor_ with a little _croton oil_ throws out a spray, which in a few moments unites into a thin film. The spray, as it spreads, draws out the inner portion into radiate points, which open into a beautiful network, the centre cohering closely.

"_Croton oil_ throws out, in spreading, a fine spray in advance of the more closely cohering portion, which follows quickly. The outer edge breaks up unevenly into little indentations, the border of the inside portion being quite broken, but gradually becomes nearly entire. The surface, too, has openings, which increase quite rapidly in size, the outer ones being much the larger. In the final breaking up, before the holes open one into another, the outlines are beautifully fringed.

8. "Spontaneous combustion ensues when a handful of cotton waste is embued with oil and placed in an air bath at 130 to 200 F. Boiled linseed oil required 1-1/4 hour; raw linseed oil, 4 hours; lard oil, 4 hours; refined rape about 9 hours."[52]

[Footnote 52: J. J. Coleman, 'Journal of Applied Chemistry,' Dec., 1874.]

Mr Gellatly found that an admixture of 20 per cent. of mineral oil r.e.t.a.r.ded combustion, and 50 per cent. prevented it completely.

M. Burstyn,[53] believing that the value of a fatty oil as a lubricant depends on the amount of acid it contains, has invented a method for volumetrically determining the acidity. The process is as follows:--A tall cylindrical vessel, provided with a ground-gla.s.s stopper, and having two marks on it to indicate respectively 100 cubic centimetres, and 200 cubic centimetres, is filled to the first mark with the oil to be tested, and to the second mark with 88 to 90 per cent. alcohol. The cylinder is then closed and well shaken. Equal quant.i.ties other than 100 cubic centimetres can be employed without any other change in the process. After standing two or three hours the oil settles, and the clear alcohol, which contains in solution the free acids and a little of the oil, rises to the top perfectly clear; 25 cubic centimetres of the clear alcohol is taken from the top by means of a pipette. A few drops of alcohol extract of turmeric is added, and the acid determined by means of a standard solution of potash, as in acetometry. The change from yellow to brownish red takes place with great sharpness when neutralisation is reached.

[Footnote 53: Ure's 'Dictionary of Arts,' &c.]

The number of cubic centimetres of potash employed, multiplied by four, gives the quant.i.ty of normal solution requisite to neutralise the free acid in 100 cubic centimetres of oil. As it is not an individual acid, but a variable mixture of acids, it is not possible to calculate the percentage of acids present. These numbers, however, may be taken as degrees of acidity. For instance, an oil of 3 of acidity is one which contains enough free acid to neutralise 3 cubic centimetres of normal alkali.

If we a.s.sume that oleic acid predominates, which in most cases is the fact, 1 of acidity correspond to 028 per cent. by weight of oleic acid.

The olive oil of commerce has an acidity ranging from 04 to 12. The first pa.s.ses as very fine, and is called free from acid or salad oil, while the latter is known by smell and taste as very rancid. Oil that has 4 to 6 of acidity has been found to answer very well as a lubricator.

What relation there exists between the degree of acidity and any injurious effect upon metals is shown by the following experiments:--Four shallow vessels of sheet bra.s.s, having a surface of 40 square centimetres each, at the bottom, were filled to the depth of 2 millimetres, with oils of different acidity, and exposed to the air at the ordinary temperature. The vessels were soon more or less covered with green fatty salts, and the oil too acquired a green colour. Oil and vessel No. 1 were the only ones in which no change could be perceived. At the end of 3 days the vessels were cleaned with ether and weighed. The following table shows the amounts of action:

Vessel No. 1, filled with oil of 08 lost 003 gr.

" No. 2, " 46 " 022 "

" No. 3, " 78 " 036 "

" No. 4, " 88 " 004 "

The quant.i.ty of metal destroyed, in equal times and under equal conditions, increases with the acidity of the oil.

The table on page 1128, by Mr Bottome, describes the most striking physical properties of some of the princ.i.p.al fixed oils.

? The following are the princ.i.p.al fixed oils met with in commerce, or which are objects of interest or utility:

=Oil of Al'monds.= _Syn._ OLEUM AMYGDALae (B. P., Ph. L), O. AMYGDALARUM (Ph. D.), O. AMYGDALI COMMUNIS (Ph. E.), L. "The oil expressed from the kernels." (Ph. L.) "Bruise the fresh almonds in a stone mortar, then put them into a hempen sack, and express the oil, without heat." (Ph. E.) The oil of almonds B. P. and of commerce is obtained from either the bitter or sweet almond, but chiefly from the first, on account of their less value, and the marc being employed in the manufacture of essential oil.

_Prop., &c._ Oil of almonds is black, demulcent, emollient, and nutritious; possesses a purely oleaginous taste, and is one of the most agreeable of the fixed oils; when taken in quant.i.ty it is mildly laxative; it is little affected by cold, and congeals with difficulty; is soluble in 35 parts of cold and 6 parts of boiling alcohol; ether dissolves it freely. Sp. gr. 915 to 918. _Av. prod._ Sweet almonds, 46%; bitter a., 41%.

_Pur._ It is extensively adulterated with poppy, nut, and teel oil, and not unfrequently with refined rape or colza oil. (See _above_.)

=Oil of Bay.= 1. (EXPRESSED O. OF B.; OLEUM LAURI, O. LAURINUM, L.) By expression from either fresh or dried bayberries, as castor oil. Limpid; insipid.

2. (By decoction; b.u.t.tER OF B.; OLEUM LAURI n.o.bILIS, O. L. VERUM, L.) From the berries, by boiling them in water, and skimming off the oil. Green, b.u.t.tery; chiefly imported from Italy. Used by the vulgar in bruises, sprains, rheumatism, deafness, &c. _Prod._ 20%.

=Oil of Beech.= _Syn._ OLEUM f.a.gI, L. From the nuts of _f.a.gus sylvatica_ (Linn.) or beech mast. Clear; keeps well; when washed with hot water, it is used for salads, and burnt in lamps. Sp. gr. 9225. _Prod._ 16%.

=Oil of Belladon'na.= _Syn._ OLEUM BELLADONNae SEMINUM, O. B. BACCae, L.

From the seeds or berries of _Atropa belladonna_ or deadly nightshade.

Yellow; insipid. Used for lamps in Swabia and Wurtemberg, and as an application to bruises. The marc is poisonous. It freezes at 34 Fahr. Sp.

gr. 9250.