Preparation of Syrups by Percolation.



The Pharmacopoeia gives formulae for twenty-three syrups. They are not all finished by the same process, but to dissolve the sugar different degrees of temperature are used. A few are finished by dissolving the sugar at a boiling heat, a portion by effecting solution with a gentle heat (90° to 100°F.), another portion by agitating a previously prepared tincture, from which the alcohol has been evaporated, with the sugar occasionally until solution is effected, and still another portion by mixing a fluid extract, solution or tincture with simple syrup. So we see that four different methods are directed, and it is striking that, except in a few only, the use of a high temperature appears to be avoided as much as possible. It seems that in these preparations the Pharmacopoeia would have dispensed with heat altogether, if it had been sure that by adopting the cold process for all unexceptionable products would be obtained.

In the following the writer proposes to give some of his experience in regard to percolation (cold) of syrups, which has been practised in his establishment for about nine years with uniform good results.

Percolation, fifteen or twenty years ago, was among pharmacists a comparatively novel process; a good many even to this day regard it with aversion and suspicion because they think it more troublesome than the old process, and because they do not believe that by it as good and strong a product can be obtained. It is doubtful whether percolation was practised by a half dozen pharmacists of our city at the time mentioned above. Still, since its adoption by the Pharmacopoeia, it has gained ground steadily, and those who practise it sufficiently long to find out its merits, especially for the preparation of fluid extracts, will not return to the old process for any consideration. To make a fluid extract the Pharmacopoeia directs to exhaust some root, herb, etc., of a prescribed degree of fineness, by percolation. To accomplish this so as to secure an unexceptional preparation requires not only the careful and judicious selection of the drug, but also due care in manipulation; in fact, it requires a considerable amount of experience. To make syrups by percolation successfully requires not nearly so much experience. If certain conditions in the construction of the apparatus are attended to the rapidity of the solution of sugar by the process varies only in so much as the menstruum may be more or less viscid. Since the Pharmacopoeia directs to exhaust roots, herbs, gums, etc., by percolation, requiring quite an amount of care, attention and experience, why should not the simple solution of sugar be effected by the same process, since this, in comparison, requires little attention, furnishes a product unexceptional in appearance and superior in flavor (in such as have volatile ingredients) to those made by heat? Syrups are also made by agitating or shaking together the sugar and menstruum. But, in the first place, it takes longer to dissolve sugar by this process than by percolation, and, secondly, if any quantity of air is incorporated the tendency to spoil is accelerated. When syrups are prepared by boiling they, or at least quite a number, need constant supervision to prevent waste by boiling over; with ever so much attention to cleanliness, the straining cloths will still often be found defective, and when the hot syrup is strained into a glass vessel too much care can hardly be exercised to prevent breakage. Straining through even close cloth does not furnish an absolutely clear syrup. In percolation breakage of vessels by heat is out of the question, and the product has (when the process has been properly conducted) the perfect clearness attained by filtering through paper. When the simplicity and cleanliness of the process is contemplated, the conclusion is irresistible that it ought to have been adopted by the Pharmacopoeia. Furthermore, it would be but consistent to direct the process by which the soluble parts of substances, apparently difficult of solution, are extracted, for the mere solution of sugar, which is not at all difficult to dissolve. Percolation is also illustrated to perfection when sugar is dissolved by the process.

Percolation of roots, herbs, etc., with an aqueous, spirituous or ethereal menstruum, and that of sugar by water, an infusion, decoction, a partly spirituous or otherwise tincture, cannot be conducted in the same manner in every particular. Undoubtedly, because this has often been attempted failure was the result. Writer of this, about nine years ago, read in some pharmaceutical journal (I believe it was the "Pharmacist," of Chicago) about the preparation of syrups by percolation, and thought the idea capital. The process was tried at the first opportunity with simple syrup. The percolator was charged, as usual, with a wad of cotton in the neck, a cork in the orifice, loaf sugar and water, adjusted on a filtering stand, and set aside until the sugar had all been disintegrated and settled. The cork was then removed, and it was expected that percolation would proceed without any trouble; but it did not. Having obtained 2 fluidounces of syrup in 12 hours the process was discontinued and the syrup finished by boiling. Using cotton wads for the percolation of syrups was found an utter failure. In subsequent operations sponge wads were substituted, and with entire success. A piece of common close, soft sponge is trimmed to a cone shape, ½ , 1 inch or longer, and ½ , 1, 2 or more inches diameter. The sponge is thoroughly washed and while still moist placed in position in the neck of a percolator, funnel or other suitable vessel by slightly compressing it. Sponges with small pores need little and such with large pores need more compression in adjusting. If it is placed too loose the syrup will pass too fast and not sufficiently clear, if placed too tight the syrup will pass too slow or not at all. The proper amount of compression is reached when the pores of a close sponge 1 inch long and ½ inch in diameter are closed in such a manner by adjustment in a ⅜ inch necked common half-gallon glass percolator that one pint of syrup will percolate in an hour. According to the size of the sponge, its compression, the size of the neck of the percolator, and its capacity, less or a great deal more may be obtained. When definite quantities of syrups are made, towards the end of the process the sugar must be heaped towards the centre of the percolator, because, since the process of displacement progresses faster in the centre over the orifice than at the circumference of the percolator, the sugar is dissolved fastest there, and when dissolved down to the sponge allows the menstruum to pass without dissolving the balance. In a continuous process this precaution is unnecessary. By percolation, when properly conducted, syrups are obtained absolutely clear, just as if filtered through paper.

Some of the syrups of the Pharmacopoeia cannot be prepared by any other than the cold process, for instance syrupus allii, syrupus pruni virginianae, and with these, as also with fruit syrups, percolation may be considered the ne plus ultra of perfection. In most of the syrups of the Pharmacopoeia filtration can be combined with percolation. For instance: It is not necessary to filter the aqueous tincture of orange peel when syrupus aurantii corticis is prepared, but after adding water to the evaporated portion, as directed, the turbid liquid may be immediately percolated with the sugar; or, for syrupus ipecacuanhae, two fluidounces of fluid extract of ipecacuanha are diluted with 12 fluidounces of water and, without filtering, may be percolated with 26 troyounces of sugar for 32 fluid-ounces of syrup. In each case a transparent syrup results. Syrupus scillae compositus may be prepared in two ways. The tincture of seneka and squill is prepared by percolation, then evaporated to half a pint and 14 ounces of water added, just as the Pharmacopoeia directs. To this the tartrate of antimony and potassium is added, or the latter can also be dissolved in the water before mixing with the evaporated solution; the mixed solution is then percolated with 42 troyounces of sugar, and sufficient water is added through the percolator until the percolate measures three pints. Another method is to use the fluid extract of squill and seneka, and proceed the same as above. Both methods furnish good products, only the latter contains some alcohol from the fluid extracts which the former does not.

Syrupus Ferri Iodidi.—The filtered solution of iodide of iron, prepared from 2 troyounces iodine, quant, sat. of iron and water, measuring 10 fluidounces, is percolated with 16 troyounces of sugar, and, if necessary, sufficient distilled water is added to make the product measure 20 fluidounces. In this instance a filtered solution is preferable, although one not filtered could be used.

The other syrups of the Pharmacopoeia can be made in the same manner, using for each the tincture or aqueous solution, as directed, and then percolating with sugar, either the quantity prescribed or as much as the syrup ought to contain.

A goodly number of physicians prescribe fruit syrups, such as raspberry, strawberry, etc. The exquisite flavor of these is preserved to the possibly fullest degree by percolation. It is inexcusable for an apothecary to dispense, in prescriptions, the artificial preparations. During the respective seasons of the fruits any convenient quantity of fresh, ripe fruit is expressed, the expressed juice is allowed to ferment and percolated with sugar quant, sat. Strawberry syrup was prepared as follows.: A gallon of fresh, plump fruit, after being pounded into a pulp of uniform consistency, in a porcelain mortar, was put into a glass covered vessel and allowed to ferment. This, according to the estate of temperature, may take from 3 to 5 days. To accelerate and complete the process of fermentation the vessel ought to be shaken once or twice a day, to reincorporate the mass which gathers on the surface of the juice. When fermentation has been completed this mass will generally settle to the bottom of the vessel. When the expressed fruit juice is fermented no shaking is necessary; but the work of gaining the juice by pressure is exceedingly tedious, on account of the gelatinous consistence (pectin) of the fruit, which allows the pressure to be but very slowly and gradually applied. If the pressure is applied sudden and powerfully, the press bag or cloth will be torn invariably. On account of this drawback it is more expedient to ferment the crushed fruit and then express. Fermentation can be observed and its cessation determined to a nicety if a glass bent tube inserted air tight in the cork of the vessel containing the fruit and its free arm is made to dip about one-half inch into water contained in a small glass vial, when the finishing of fermentation is indicated by cessation of evolution of carbonic acid gas escaping through the glass tube under water in small bubbles. The expressed, fermented juice from the gallon of strawberries measured 2 ¾ pints. This was percolated with 72 troyounces loaf sugar. The resulting syrup measured 5 pints. Raspberry syrup was prepared in the same manner. Of both syrups, prepared in the summers of '78 and '79, I have some on hand now, which, in the summer gone by, was exposed to a temperature of between 80° to 85° Fahr. without spoiling. To insure the keeping qualities of syrups prepared by percolation from fermented fruit juices, it is of paramount necessity to use only such juices in which fermentation has been complete. They (the syrups) ought also to hold in solution a sufficient quantity of sugar. Percolation regulates this to a nicety; by it as much sugar will pass into solution as can be conveniently held, and this is the best criterion of how much sugar a syrup ought to contain. Percolated syrups will not deposit any crystalized sugar in the bottles, except if they are exposed to a continuous low temperature.

The German Pharmacopoeia directs heating to the boiling point for most of its syrups. It is asserted by some that syrups ought to be boiled, or heated to the boiling point, to effect precipitation of impurities. Our Pharmacopoeia does not seem to be of the same opinion, since, with the exception of only a few, it either employs a gentle heat (90° to 100° F.) or none at all. Furthermore, it is obvious that the use of heat would, in some of the syrups, totally destroy the medicinal properties for which they are generally prescribed, and in some which have flavors of extreme volatility these would be more or less impaired.

Lowell, N. St. Louis, Mo., Dec., 1880.

The American Journal of Pharmacy, Vol. 53, 1881, was edited by John M. Maisch.