Part 158
=EXPER'IMENTS= are acts or operations intended to develop some unknown fact, principle, or effect; or to establish or demonstrate it, when discovered. Similar operations, performed merely for amusement, are also often, though incorrectly, called by this name. In rational experiments these two objects are combined. To experimental research is due the present high state of advancement and usefulness of the various sciences most intimately connected with our happiness and well-being. The danger of taking things for granted has been thus pleasantly and instructively pointed out by Archbishop Whately:--"It was objected to the system of Copernicus, when first brought forward, that if the earth turned on its axis, as he represented, a stone dropped from the summit of a tower would not fall at the foot of it, but at a great distance to the west; in the same manner as a stone dropped from the masthead of a ship in full sail does not fall at the foot of the mast, but towards the stern. To this it was answered, that a stone, being a part of the earth, obeys the same laws, and moves with it; whereas it is no part of the ship, of which, consequently, its motion is independent. The solution was admitted by some, but opposed by others; and the controversy went on with spirit; nor was it till one hundred years after the death of Copernicus that, the experiment being tried, it was ascertained that the stone, thus dropped from the head of the mast, _does_ fall at the foot of it."
=EXPORTATION.= (EXPORTATION ON DRAWBACK.) By law, a certain allowance, or drawback of duty, is payable on certain articles, when exported from any part of the United Kingdom, either as merchandise or ship stores. Thus:--
SUGAR, refined in the United Kingdom, from 4_s._ to 6_s._ per cwt., according to quality.
TOBACCO, manufactured in the United Kingdom, 3_s._ 3_d._ per lb. The full drawback is only allowed on normal tobacco, which contains 13 per cent. of moisture. If the moisture exceeds 13 per cent., a proportionate reduction is made in the drawback; if it is found less than 13 per cent., a proportionate increase is granted.
SNUFF is entitled to drawback at 3_s._ 3_d._ per lb., subject, however, to an increase if the moisture is less than 13 per cent., and the inorganic matter not over 18 per cent., and to a decrease if the moisture in organic matter exceeds these per-centages.
BEER. The amount of this drawback is proportional to the quantity of malt or sugar used in the brewing of the beer, and is nearly equivalent to the duty originally paid on such malt or sugar. It is computed according to the following scale:--For every barrel, or 36 gallons of beer, the original gravity of which was not less than 1040°, a drawback of 4_s._ 3_d._, and for every additional 5 degrees, from 1040° to 1125° inclusive, a further sum of 6_d._ per barrel.
SOLIDIFIED WORTS, made by a licensed brewer, from malt or sugar, or malt and sugar, a drawback of 2_s._ 10-5/100_d._ per 28 lbs.
MALT. Under certain restrictions, a drawback of the duty charged, after deducting 7-1/2 per cent. of the measured quantity.
SPIRITS, from 10_s._ to 10_s._ 3_d._ per proof gallon.
In all cases samples are taken by the Custom House officer, and forwarded to the Inland Revenue laboratory, where they are examined previous to the payment of the drawback.
=EXPRES'SION.= In the _useful arts_, the mechanical operation by which a fluid contained in the pores or cells of a solid is pressed out or expelled. Many of the fluid substances employed in pharmacy and chemistry are obtained by expression. Thus, the unctuous vegetable oils, as those of almonds, linseed, &c., are procured by submitting these substances to powerful pressure between iron plates, which are either made warm, or the bruised seeds are previously exposed in bags to the steam of boiling water. The juices of fresh vegetables are also obtained by expression. The substances are first bruised in a marble mortar, or, on the large scale, in a mill, and immediately submitted to the press, to prevent them passing into a state of fermentation, which would injure the quality of the product. Fruits which contain highly flavoured or fragrant seeds, or which have rinds containing essential oil, are generally deprived of them before being sent to the press. The subacid fruits are also allowed to lay together for some days before pressing them, as the quantity and quality of the product is thereby increased. The fluid matter absorbed by the ingredients employed in the preparation of tinctures, infusions, decoctions, extracts, &c., is generally obtained by powerful pressure. Expression is also frequently had recourse to for the purpose of obtaining solids in a state of purity, as in the expulsion of olein from stearin, water from bicarbonate of soda, &c. On the small scale, the common screw-press, or one of like construction, is usually employed; but the power thus obtained is insufficient to expel the whole of a fluid diffused through the pores of a solid. Hence has arisen the use of the hydraulic press, which is now almost alone employed on the large scale. In all these cases the substances are placed in bags made of haircloth, or coarse canvas, previously to their being submitted to pressure. For tinctures and like pharmaceuticals, a small screw-press (TINCTURE PRESS) made of 'galvanised' or tinned iron, and varying in capacity from 1 quart to several gallons, is employed.
=EXSICCA'TION.= See DESICCATION.
=EX'TRACT.= _Syn._ EXTRACTUM, L. Among _chemists_ this term is understood to apply to the residuum of the evaporation of aqueous decoctions or infusions of vegetable matter. In _medicine_ and _pharmacy_, it has a less definite signification, being applied to various preparations obtained by evaporating the expressed juices, or the decoctions, infusions, or tinctures of vegetable substances, until a mass, of a solid or semi-solid consistence is formed. Extracts vary in their nature and composition with the substances from which they are prepared, and the fluids employed as solvents. When water is employed as the menstruum, the products (AQUEOUS EXTRACTS, WATERY E.; EXTRACTA AQUOSA, E. SIMPLICIORA, L.) usually consist of gum, starch, sugar, albumen, extractive and saline and other matter, along with the peculiar principles on which the medicinal virtue of the vegetable depends. When spirit is employed as the solvent, the products (ALCOHOLIC EXTRACTS; EXTRACTA ALCOHOLICA, L.) contain most of the substances above enumerated, except the gum and starch, together with several other substances which are soluble in spirit, but which are either wholly or nearly insoluble in water; as resins, essential oils, and the proximate principles of vegetables. These preparations, with scarcely an exception, are considerably more powerful than the aqueous extracts of the same vegetables. In some cases proof spirit or under-proof spirit is employed, when the extracts (SPIRITUOUS EXTRACTS; EXTRACTA SPIRITUOSA, L.) generally possess properties between those of the above. In other cases, dilute acetic acid or acidulated water is employed as the menstruum, when the products (ACETIC EXTRACTS; EXTRACTA ACETICA, L.) possess much greater activity than when prepared with water; and would in many cases prove fatal, if exhibited in doses as large as those of the aqueous extracts. Still more active extracts are obtained by a combination of the last two menstrua. According to Ferrari, plants treated with rectified spirit of wine, mixed with 1/36th part of acetic acid, yields extracts of remarkable activity. On the Continent ether is sometimes used as the menstruum for the active principles of certain substances, as cantharides, cubebs, worm-seed, &c. (ETHEREAL EXTRACTS; EXTRACTA ETHEREA, L.) The term 'simple extract' is applied to an extract prepared from a single plant or vegetable substance, and the term 'compound extract' to one prepared from two or more of such substances. The FLUID EXTRACTS (EXTRACTA FLUIDA, L.) of modern pharmacy are those which are only evaporated to the consistence of a thin syrup, and then mixed with 1-10th to 1-8th of their volume of rectified spirit.
_Prep._ The preparation of medicinal extracts may be conveniently considered under two divisions, viz.--1. The production of a solution of the soluble portion of the substances operated on; and, 2. The reduction of this solution by evaporation to the consistence of an extract.
1. PREPARATION OF SOLUTIONS:--The preliminary operations in the manufacture of extracts are similar to those employed in the preparation of DECOCTIONS, INFUSIONS, and TINCTURES. The proper quantity of the ingredients being taken, the whole is well bruised or reduced to coarse powder, or otherwise divided by slicing with a knife, that every portion may be fully exposed to the solvent action of the fluid. In some few cases (as with gentian, &c.) the 'slicing,' or reduction to fragments, is often conveniently deferred until the action of the menstruum shall have so far softened the ingredients as to render them of easy division by the knife. Those substances (as sarsaparilla, chamomiles, &c.) whose medicinal principles reside in the cortical portion, of which are of easy solubility, are commonly subjected to the action of the menstruum without being subjected to any particular preparation.
In the preparation of AQUEOUS EXTRACTS, the ingredients are treated with water until all the soluble matter that it is desirable to obtain is dissolved out. There are several methods of effecting this object, depending upon the nature of the substances acted on. In some cases maceration in cold water is resorted to; in others percolation with that fluid in a 'displacement apparatus.' More generally, however, boiling water is poured on the substance, and is digested on it for some time, as in the preparation of infusions; or the substance is exhausted by boiling in water, as in the preparation of decoctions. After the ebullition or infusion has continued a sufficient time, the heat is removed, and the liquid portion drawn off. The ingredients are then pressed to extract the remaining liquid; or they are washed or 'sparged' with hot water, which expels it by displacement. According to the usual practice in the majority of cases, a second quantity of water is poured on after the first has been thoroughly drained off, and the effusion or decoction is repeated a second and even a third time, or until the ingredients are perfectly exhausted of their soluble portion. The liquor or liquors thus obtained being allowed to repose for 15 or 20 minutes, for the purpose of depositing the sand or other gritty and heavy matter that is mechanically mixed with them, are carefully decanted from the sediment, and, after being run through a fine hair-sieve, or flannel bag, are ready for concentration. In some instances, however, this method proves insufficient to render the liquid clear. In such cases, the solution may generally be rendered transparent by clarification with a little white of egg, removing the scum as it rises, straining the liquid through flannel, as before; or the liquid may be filtered through a bag made of fine 'Welsh flannel,' or of 'tweeled cotton cloth' (Canton flannel), both of which should be soaked in clean water for at least an hour before use. In the small way, filters of linen or paper are sometimes employed; but as all media sufficiently fine to render vegetable solutions transparent soon choke up, this filtration is objectionable, from the length of time it occupies. In some houses the aqueous infusion or decoction is allowed to repose for 24 hours, and then decanted and evaporated; but such a plan is objectionable, as, however smooth and glossy extracts so prepared may appear, their medicinal virtues are lessened by the lengthened exposure to the atmosphere.
When about one half of an aqueous solution has evaporated, it is often advantageous to repass it through a flannel or horsehair strainer, to remove the flocculi that generally form by the action of the heat and air. This is especially necessary with vegetable solutions prepared without boiling, and should be adopted whenever a smooth and slightly extract is desired.
II. REDUCTION OF SOLUTIONS:--The reduction of the solution to the proper consistence is effected by evaporation. The mode in which this is performed varies for different extracts. The London College directs that, "unless otherwise ordered, the evaporation should be conducted as quickly as possible, in a broad, shallow pan, placed in a water bath, until a proper consistence is acquired for forming pills; stirring assiduously with a spatula towards the end of the operation." The Dublin College orders that "all simple (aqueous) extracts (EXTRACTA SIMPLICIORA), unless otherwise ordered, are to be prepared by boiling the vegetable matter in 8 times its weight of water, till the liquid is reduced to one half; the liquor is then to be expressed, and, after a short time allowed for defecation, to be decanted, filtered, and evaporated in a steam or water bath, until it begins to thicken, and then finally inspissated by a reduced heat, with continual stirring, until a consistence for forming pills be attained." The instructions of the Edinburgh College are similar, with the one important exception, however, of ordering the evaporation to be conducted in a water bath saturated with chloride of sodium.
Though the water bath has the sanction of the London College, it is ill adapted for the purpose to which it is here ordered to be applied, as from its low evaporative power the advantages which are derived from its equable temperature are vastly overbalanced by the lengthened exposure of the solution in a heated state to the action of the atmosphere. It has been shown that a vegetable extract so prepared is inferior in quality to a similar one formed by rapid evaporation in a shallow pan over a naked fire, or placed in a sand bath, provided proper care is taken, and assiduous stirring is adopted during the whole time of the exposure to heat. In practice, however, the use of a naked fire is perfectly inadmissible, as the least neglect on the part of the operator would probably lead to the incineration of the whole. These objections are obviated by the addition of the 1/5th part of salt to the water of the bath, which raises its boiling-point to 218-3/4° Fahr., when the temperature of the contained extract is fully 212°; the remaining 6° being lost by the interposition of the substance of the evaporating vessel.
ON THE LARGE SCALE, the evaporation of infusions or decoctions for extracts is usually conducted in very wide, shallow, copper or tinned-copper pans, having steam-tight jackets of cast iron, and heated by steam 'playing' between the two.
The rapid deterioration which vegetable juices and solutions undergo by exposure to the air, especially at high temperatures, has led to the introduction of apparatus, by which they may be concentrated without contact with the atmosphere, and at a less degree of heat than is required for that purpose in open vessels. Such is the method, commonly called 'Barry's process,' in which the air is removed from certain air-tight refrigerators by the introduction of steam, which is then condensed by the application of cold, by which means a partial vacuum is obtained. Another process for attenuating the atmosphere over the surface of fluids during evaporation is by the action of an air-pump. This plan was introduced by Howard, and is commonly applied to the concentration of syrups in the sugar refineries. Extracts obtained by either of these methods are said to be prepared 'in vacuo,' and are found in practice to be immensely superior to the common extracts of the shops, and consequently require to be exhibited in proportionably small doses.
'The American Journal of Pharmacy' for September, 1877, contains a new process for the preparation of extracts without heat, by Professor Herrara. We extract the following from the Professor's paper:--
"The results of my observations have satisfied me that, when the water partially congeals, the dissolved principles remain in solution in the mother liquors, and that two or three congelations are generally sufficient for obtaining the solutions concentrated enough to finish the extract by exposure upon plates to the heat of the sun, or of a drying closet, heated to about 30° cent. (86° Fahr.). The extracts prepared by this method accurately represent the properties of the plants, and the principles which are changed by the influence of heat remain unaltered; even the volatile constituents are not dissipated, though most of the water be removed by freezing. Owing to the small cost of the necessary apparatus, it appears to me that my process for preparing extracts should be preferable even in those countries where ice is less readily obtainable than combustibles.
"Extract of conium prepared with unpurified juice by the process mentioned, has preserved the characteristic odour of conia, and by dissolving it in water. I have obtained a solution exactly representing the juice of the plant in appearance and properties, and giving when heated an abundant coagulation, proving that even albumen had remained unaltered. 1750 grams of cow's milk at 9° R., left, after three congelations, 750 grams of a liquid having a density of 148, and by evaporation in the sun this left a dry extract of milk, which again formed that liquid on being dissolved in water. A number of other liquids similarly treated, gave corresponding results, and it seems to me, therefore, that medicinal extracts are best prepared by congelation. It may be objected that the medical juices should be previously purified, but it should be remembered that coagulated albumen always encloses a considerable portion of the active principles, and that the heat necessary to effect the coagulation and the evaporation by means of a water-bath is sufficient to change many principles; also that the extracts thus prepared are sometimes inert or less active. The careful experiments made by Orfila and the clinical experience of others demonstrate that extracts prepared with unpurified juice are stronger.
"The apparatus employed by me is the so-called sorbetière;[294] for larger quantities the apparatus of Gougaud is preferable. The frigoric mixture is composed of ice and sodium chloride, or preferably of crystallised calcium chloride. After a large portion of the solution has congealed, the mass is enclosed in a cloth and subjected to pressure, the press-cake of ice is broken and again pressed, to separate the mother liquor as completely as possible, and the congelation is repeated two or three times, with the precaution that it is not carried far enough to cause the precipitation of the sparingly soluble principles. The mother liquor is then put into shallow dishes and exposed to the heat of the sun or of a drying room, the temperature of which does not exceed 30° C. (86° F.) until the extract has attained the desired consistence."
[Footnote 294: An apparatus similar to that used for ice-cream.]
_Obs._ When water, acidulated with acetic acid, is employed in the preparation of extracts, the vegetable substances are usually macerated in it, in the cold, or the dilute acid is sprinkled over the bruised plant in the fresh or recent state, and the whole is then submitted to strong pressure, to expel the juice, which is strained and evaporated in the usual way, but preferably in a well-tinned or plated-copper pan.
ALCOHOLIC and SPIRITUOUS EXTRACTS are prepared by evaporating a filtered concentrated tincture of the ingredients in any suitable vessel, by which the volatilized spirit may be saved. In general, rectified spirit is used as the menstruum; but in some cases proof spirit is employed; and, in others, the substances are first digested in proof spirit, and afterwards in water, and the mixed tincture and infusion evaporated in the usual manner.
ETHEREAL EXTRACTS are obtained in a similar manner to alcoholic ones; but being merely prepared in small quantities at a time, the process may be conveniently performed in glass vessels. When it is required to boil either of the above fluids (alcoholic or ethereal), or any other volatile liquid on the ingredients, a vessel fitted with a long tube, or a Liebig's condenser reversed, as noticed under ether, may be used to prevent any loss of the menstruum.
The INSPISSATED VEGETABLE JUICES (JUICES, E.; SUCCI, L.) of the British Pharmacop[oe]ia are obtained by expressing the juices from the fresh plants, and preserving them by the addition of spirit. "By thus preserving the juice of the plant its properties are not impaired by the action of the air during the time necessary to dry the leaf for tincture, nor by the action of both air and heat during the time necessary to evaporate the juice to the consistence of an extract."--Squire. The directions of the Edinburgh College for preparing their inspissated juices (SUCCI SPISSATI, L.) are--"Beat the fresh substance, and press it strongly through a canvas bag, in order to obtain the juice; which, being put into a wide, shallow vessel, and heated by means of boiling water saturated with sea-salt, is to be reduced to the consistence of honey. The mass, when cold, is to be put into glazed earthen vessels, and moistened with strong alcohol." By operating in this way a considerable portion of the activity of narcotic vegetables is lost. Some of their juices, as that of aconite, are impaired in so short a time as scarcely to compensate for the trouble of preparing them. This deterioration does not, however, take place in any remarkable degree, if the expressed juice from the recent vegetable be evaporated by exposing it in a thin stratum to a current of very dry air, as adopted by Mr Squire. This may be managed by putting the juice into small, flat trays or dishes, placed on shelves in a suitably arranged apparatus, alternated with similar vessels of concentrated sulphuric acid; or by causing a current of very dry air, at the common temperature of the atmosphere, to pass over them. It has been shown that 10 gr. of extract, thus prepared, were more than equal to 20 gr. prepared _in vacuo_; and to more than 60 gr., and in some cases, 90 gr., of those prepared by the common process of boiling down the juice to an extract.