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equivalents of morphia, as a very slight addition of acid gives to its solution an acid reaction. If the salt contains one equivalent of morphia, the per centage of precipitate, which should be yielded by treatment with ammonia is, 69.6, if two equivalents it is 80.0, and if three, 84.0: that obtained, however, was 74, which is therefore incorrect, and the experiment cannot be depended upon. Taking the salt to be a neutral one, that is to say, to be composed of two equivalents of morphia, with its combined water, and one equivalent of water as bases, and one equivalent of phosphoric acid (P2O5), then the number of equivalents of water of crystallization (as indicated by the loss of weight by heating the salt over a water-bath) is ten, and the formula of the salt is two (M, HO), H O, P2 O,+10 Aq.=767.86. This gives 11.8 per cent. of water of crystallization: the loss by heating was, as stated in the above first experiment, thirteen, and in the second twelve, per cent.

2

3. ACID-TARTRATE OF MORPHIA.-This salt is prepared by dissolving morphia in a solution of tartaric acid, taking care that the latter is sufficiently in excess, concentrating by evaporation, and setting aside to crystallize. The size and the appearance of the crystals are much affected by the degree of purity, and of concentration of the solution:-the whiter the salt, the more difficult is it to obtain it in large well-formed crystals. The solution of this salt reddens litmus, and gives a white precipitate with ammonia, which is reddened by nitric acid;-the crystals are decomposed by a solution of iodic acid, setting iodine free, which yields iodide of amidine, when tested by cold mucilage of starch.

Two quantities of ten grains each were heated in a watch-glass over a water-bath for an hour, but neither lost weight; a third quantity of ten grains was exposed to the same temperature for five hours, and only lost half a per cent., which was probably only hygroscopic water.

Two quantities of ten grains each were heated with ammonia, and the precipitates collected and weighed; the first experiment gave sixty-four, and the second sixty-five per cent. of hydrated morphia.

Supposing the salt, therefore, to be a bitartrate, with two equivalents of water of crystallization, that is to say, one equivalent of acid as now received, and two equivalents on the old theory of the composition of the acid, with one equivalent of hydrated morphia (M, HO), and one equivalent of water as bases, and two equivalents of water of crystallization, the per centage should be 67 of hydrated morphia, thus

1st Experiment gave...........

2d Experiment gave.....

(M+2HO) per cent.

64

65

Calculation gives (M HO,+2T+2Aq.=453.19)...... 67

4. NEUTRAL TARTRATE OF MORPHIA is formed by saturating a solution of tartaric acid with morphia, and concentrating the liquid crystals are deposited, which are not obtained either very white or of a good form. They are very soluble in water, and adhere together in masses, which, when dried, form a cake: this cake, although of a brown colour, yet yields a white powder. The solution of this tartrate restores the colour to reddened litmus paper :-ammonia precipitates morphia.

Ten grains of this salt, dried at a temperature rather higher than the ordinary one, were exposed to the heat of a water-bath for five hours, and lost 0.35 grains, which are equal to 3.5 per cent. If the salt be a neutral tartrate, and we suppose the loss by heating to represent the water of crystallization, the number of equivalents of that water is 3, and the formula of the salt will be (2M HO)+T+3 Aq.=699.94. According to this formula, the per centage of water of crystallization is 3.6.

Experiment gave.

3.5 per cent. loss by heating

Theory of 3 equiv. of water of crystallization gives. 3.6 This variation of 0.1 per cent. would result from an error in the experiment amounting only to one hundredth of a grain, whereas one-tenth of a grain was the smallest weight employed. The quantity of morphia was not experimentally determined.

5. HYDRIODATE OF MORPHIA is readily made by mixing strong solutions of iodide of potassium and of hydrochlorate of morphia, and stirring the mixture-the hydriodate of morphia falls down, and must be collected on a filter, washed with a small quantity of cold water, pressed between folds of bibulous paper, redissolved in hot water, and the solution allowed to crystallize; or it may be prepared by mixing weaker solutions (in which case no precipitate falls) evaporating the mixture, and setting it aside that crystals may form; these crystals must be washed with a little cold water, pressed between folds of paper, and recrystallized. The salts should be employed in the proportion of two parts hydrochlorate of morphia, and one part of the iodide of potassium, or rather more of the latter salt may be used, as if the hydrochlorate be in excess, crystals of it will be mixed with those of the hydriodate.

The crystals of the hydriodate are white silky prisms. The solution of this salt restores the blue colour to slightly reddened litmus, precipitates morphia when ammonia is added, and indicates the presence of iodine by chlorine and mucilage of starch.

Ten grains of the salt heated for two hours over a water-bath, lost 0.35 grains, and another quantity of ten grains, heated in the same manner for five hours, lost 0.45 grains, the first being equal to 3.5 per cent., and the second to 4.5 per cent. The quantity of morphia obtained by precipitation fell short of that indicated

by theory. If we consider the salt to be composed of one equivalent of hydriodic acid, and one equivalent of morphia, with 4.15 per cent (two equivalents) of water of crystallization, its formula will be M HI+2 Aq. 447.55.

REMARKS ON THE EXPERIMENTS, BY Dr. Gilbert.

The methods employed for the determination of the composition of the above salts, it must be admitted, are somewhat imperfect; and the results, even when they agree pretty nearly with theory, can only be considered as approximations to the truth; as the only certain method is to submit the salts to ultimate analysis in the combustion tube.

The quantity of morphia was in all cases only determined by precipitating it from a warm solution of ten grains of the respective salts, by means of ammonia, stirring the mixture, and gently heating it on the sand-bath, to expel any excess of ammonia which might be added. The supernatant fluid and washings from the precipitate were evaporated to about 3ss; more ammonia was then added, and the supernatant fluid drawn off by means of a pipette, and again treated with ammonia. The liquids at the end of the process had, however, always a bitter taste, and contained morphia, owing to the solubility of that salt in the salts of ammonia-so that cach experiment always yielded less morphia than the salt actually contained. I should think that boiling the solutions of the salts with an excess of magnesia, and afterwards taking up the morphia (from the whole evaporated to dryness over a water-bath) by means of boiling alcohol, and leaving the alcoholic solution to spontaneous evaporation, might yield results somewhat more accurate than those obtained by the former process. The precipitates were collected on filters which had been dried on a water-bath for half-an-hour, and then weighed about four minutes being always allowed to elapse between taking the filter from the bath and determining the weight-so as to insure as nearly as possible an uniform condition with respect to moisture. The precipitate, after being washed on the filter, was dried under 212°, and weighed with the filter, observing the precautions already mentioned respecting the filter: the weight of the filter being deducted from the gross weight, the weight of the precipitate was known. The precipitate was, in the case of each salt, supposed to be composed of one equivalent morphia two equivalents water (M, two Aq.) for reasons stated when treating of the nitrate of morphia.

I did not employ smaller weights than one-tenth of a grain, and as ten grains of substance were operated upon in each experiment, every tenth of a grain of actual weight affected the result to the amount of one per cent, this together with the fact

of the solubility of the morphia iu the salts of ammonia, sufficiently show, that a deficiency in the quantity found by such experiments, even to the amount of several per cent. might easily occur.

The quantity of water of crystallization which the several salts contained, was supposed to be represented by the loss of weight sustained when they were heated over boiling water for some hours. It is true, that most salts do lose their water of crystallization at that temperature, if not at a lower one; but since some do not lose it at that temperature, I would not in the absence of further experiments (which I had intended, but which I had neither time nor convenience to perform) assert the perfect correctness of the above conclusion. The acidulous tartrate, although it lost nothing by heating as above described, was assumed to contain water of crystallization, because such a view reconciled the quantity of precipitate as obtained by experiment with that required by the formula.

In all the calculations it has been assumed that each equivalent of morphia was united to one equivalent of combined water, which is not separable by heating the salt at the boiling point of

water.

ON THE PREPARATION OF OXIDE OF ZINC.

BY MR. MIDGLEY.

ZINC is an abundant metal, and found in all the mining countries of Europe, Asia, and America; it frequently accompanies sulphuret of lead (galena), as sulphuret of zinc (black jack); it also occurs as calamine, oxide of zinc, &c., of late years it has been rendered malleable, rolled into sheets, and now rivals copper and tin for many purposes to which they were applied. Zinc was first manufactured in England, at Bristol, and an account of these works may be found in Nicholson's Dictionary, 4to edit., 1795. The symbol of zinc is Zn, specific gravity 7.00, it fuses at 773° Fahr. Volatile per se in close vessels, inflames in open vessels, when heated to a red heat, by combining with the oxygen of the atmosphere, and forms white flocculent particles, which were anciently called philosophers' wool.

The difficulty of collecting these particles in quantity, induced the adoption of the process of dissolving the zinc in acids, and precipitating and calcining; but I believe an oxide so formed, will not answer the purposes in medicine of that made by the direct combustion of zinc in a current of air, and that it is also much more expensive.

Many years ago, I had a demand for flowers or oxide of zinc, for medical purposes, and also contemplated its use as the basis

of paint; after various trials in crucibles of different descriptions I adopted a muffle made in parts, and luted together after being placed in the furnace. The muffle consisted of a large tile or bottom piece turned up at the edges, about sixteen inches long, and ten or eleven wide, to receive the roof or upper part formed by two slanting sides, having a flue at the top perforated with holes underneath, and an opening above, whereby the current of air may pass off, thus inducing a current of air through the muffle, during the combustion of the zinc.

When the muffle is placed and heated red-hot, the door being removed, from half-a-pound to three-quarters of a pound of granulated zinc is introduced, which shortly inflames, forming a pulverulent white oxide, which should be gently raised by the point of an iron rod, to expose the burning zinc to the current; these flakes may be removed when perfectly formed, till the whole is oxidized; the muffle should be cleared of one parcel before another is begun, in this way each operation may be finished in half an hour, and the product is a beautiful white oxide, smooth, soft, and light; it however requires washing, as it generally happens that a minute portion of metal adheres to the oxide.

If it is wanted to save the portion of oxide which would pass off by the current of air, the chimney of the muffle should be continued through the top of the furnace, and pass through a cylinder or tub, in which a little water is placed, and by connecting this tub with the chimney of the furnace a draught is secured, and the greatest part of the oxide will be obtained. The oxide of zinc is not volatile, only passes off by its levity in the current of air. These flues should be occasionally cleaned to keep up the draught, as on this the success of the operation depends. Oxide of zinc thus prepared, consists of a pure oxide and contains no foreign matter; while as all precipitates contain a minute portion of the salts used in the precipitation, however well washed, such oxide is less perfect. As a pigment, zinc being dearer than lead, to prepare a white oxide or carbonate would be too expensive for ordinary use, and it would be inferior in body. Some years ago, large quantities of native oxide of zinc were found in a cave at Ribbledale; an attempt was then made to use it as a paint by a party at Liverpool, but it was found to be defective in body, and resembled more white oil than white paint.

ON THE OXIDES OF ZINC OF COMMERCE, WITH SOME REMARKS ON THE CONSTITUTION OF BASIC CARBONATE OF ZINC.

BY MR. THEOPHILUS redwood.

THREE processes have been given in our Pharmacopoeias for the preparation of oxide of zinc. The London Pharmacopoeia

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