« 이전계속 »
a person of skill on the subject, I wrote to my late worthy and ingenious friend Dr. M'Pride, and acquainted him with the preparation I had made, and the intention of it. in his answer, he was pleased to say h. approved of the idea, and would make some of the liquor I described, and let me know what he thought of it. He afterwards wrote to me, and said he had tried the alkaline liquor, and thought it might prove an useful medicine, particularly as it might be mixed with milk and given to children, who have often acids in their stomachs. He also mentioned a physician, then in Dublin, to whom he had recommended the liquor, and who had found great benefit from it. I first made this liquor in the year 1771; and, in the year 1777, being then in Bath, I met with an account of some experiments made by Mr. Bewly, an ingenious chemist, which plainly proved that fixed air is an acid, and saturates alkaline salts; this at once informed me what it was, in the flesh of an animal, that al. kaline salts had such a strong affinity to. At the same time I got from London one of Dr. Nooth's glass machines, for impregnating water with fixed air, and to the water I added salt of tartar ; after this, I thought no more of my alkaline broth, having got a way of obtaining what I wanted in a much more elegant
The only thing now worth attention in the experiment I have related, is, that it discovered a power in even caustic alkaline salts to preserve flesh, I may say, incorruptible; though it has been gene
rally imagined that such salts would consume it. I have some flesh prepared with these salts in the year 1772; for finding some bits made the year before had continued unaltered, I made some more, and laid it by, to see how long it would keep, and what alterations it would undergo. I made it into a cake, and, when quite dry, I cut it into round bits, about the size of half-a-crown, and put them into a drawer in my desk: I shewed some of them to Mr. Kirwan the summer before last, when I had the honour of receiving a visit from him at Armagh; and a few months ago I found some pieces in another drawer, where they have lain near two and twenty years, and remain unaltered. When these pieces are broken, they hang together by fibres, and look like a piece of plaster taken from a wall; the fibrous or stringy parts of the flesh do not seem to have been corroded or dissolved by the salt.
After I knew that fixed air was an acid, and saturated alkaline salts, I began to form conjectures about the means by which these salts had so entirely prevented putrefaction in the flesh to which they were united. Animal substances afford much volatile alkali, and now they are known to contain also a volatile acid gas. While these two volatile principles continue united with each other, they may prevent any material change from taking place in the substance; but, if one of them by any means escapes, the other will follow; the acid seems to be the most volatile, and escapes first, though we may not be sensible of its escape, because it has no such strong smell as
the alkali has. The letting loose these volatile principles seems to be the beginning of putrefaction. If this be the case, we may see the reason why flesh, when growing putrid, is restored to sweetness by fixed air; that acid replacing what has escaped, and retaining the volatile alkali. It is probably on this account, that the aerial acid is found to be of use in stopping the progress of some putrid disorders; it seems to act as a sort of pickle. If vinegar preserve flesh by keeping its volatile alkali united with this acid, which is not volatile, we may expect a fixed alkali will have a like effect in serving flesh, by expelling the weaker volatile alkali, and uniting itself to the volatile acid, which will therefore be attained. This I found to be really the case; for, while the flesh and alkali were combining in the mortar, a very strong smell arose, like that of sal volatile; and, at one time that I used a brass or metal mortar, I perceived its edges to be tinged with blue, which shewed that the metal had been affected by the volatile alkali.
length of time, will be apt to run into a sort of fermentation, with an intestine motion among the mi. nute particles; this will bring on some change in the texture of the substance, and every fermentation, when long continued, ends in pu trefaction, which, indeed, is said to be the last stage of fermentation.
Whether the conjectures I have offered on this subject be well or ill founded is but of little consequence; the facts I have mentioned may be relied on.
Observations on the Nature of H ́ney, particularly on its saccharine Parts when obtained in a solid Form. By Mr. Lowitz, of the Oeconomical Society at St. Petersburg.
I. A substance so remarkable and so useful as honey, ought to have been long since accurately analyzed by the chemists. Its saccharine taste has always led them to suppose that it contained a large quantity of sugar; but the great question was, how to separate the saccharine part from the mucilaginous, and other heteroge neous parts. This separation was the principal object of my inquiry, in the experiments of which I am going to give some account.
II. The property possessed by charcoal, of decomposing and ab. sorbing the mucilaginous and phlogistic parts of various substances, (a discovery which I formerly made, and of which I then gave an ac. count), induced me to hope that I could, by its means, obtain the ob. ject I had in view. I did indeed succeed in depriving honey, which had previously been dissolved in a sufficient quantity of water, of that
smell which is peculiar to it, and also of its taste and colour; but, when I evaporated the solution, by a very gentle fire, it soon acquired its former brown colour, and did not show any disposition to produce regular crystals. I therefore thought it reasonable to conclude, that this property of recovering its original colour, either was na ural to the whole substance of honey or belonged exclusively to one of those constituent parts of it upon which charcoal had no power; for when a solution of common sugar is thickened by boiling, even though it is made to boil violently, it does not contract any colour un til all the aqueous parts are evaporated.
III. The honey which had been treated with charcoal, and thick. ened by evaporation, in the man. ner already described, was observed, two months after, to have a great number of small white lumps in it, which had the appearance of crystals; and, soon after, the whole mass seemed to be full of them. To distinguish accurately the nature of these small lumps, it was necessary to separate them from the rest of the mass, which was entirely coagulated, very thick and glutinous. This operation I performed tolerably well, by washing the mass with alkalized spirit of wine, without heat. I soon perceived that the spirit dissolved the glutinous part completely, merely by shaking the mixture; but that fluid did not seem to have any effect upon the white granulated part; so that I succeeded in obtaining this last quite pure. After having separated this saccharine granulated part from the liquor, by means of a filter, I dried it by a
gentle heat, and reduced it into powder; this powder did not at. tract moisture, and had a very agreeabie sweet taste.
IV. As the granulated consist ence of white honey seems to arise from the coagulation of its sac. charine parts, I endeavoured to separate that part by means of the purest spirit of wine, and which contained the smallest possible quantity of water. From twelve ounces of this sort of honey, I procured three ounces of saccharine matter. This matter still contained
heterogeneous substances, which appear not to be soluble in spirit of wine. To dissolve the saccharine part, I again had recourse to the purest spirit of wine I could procure; which I made use of by putting the mixture into a glass matrass, and boiling it therein for some time. By these means the saccharine part was entirely dis solved; while the insoluble part remained behind upon the filter, having the appearance of a greyish dirty slime. I had filtered the mixture while it was hot; after which I had poured the clear li quor into another matrass, in which I let it stand quiet for some days. After that time the sugar of the honey began to fix itself to the bottom of the vessel, in the form of little spherical knobs, ranged in lines by the side of each other; these, increasing in number every day, formed at last a solid crust, which was as white as snow, rather rough at the top, and which after being separated from the li quor above it, was so firm as to bear cutting with a knife into very thin slices. The remaining liquor, having been left quiet for some days, let fall, in that inter.
val, a fresh portion of this saccharine matter, which was exactly simi. lar to that already spoken of.
V. Having thus provided myself with a certain quantity of this kind of sugar, I tried various methods to make it take a regular crystallized form; but in that respect, all my trials were in vain, Whether I used the purest spirit of wine, or water, to dissolve this substance, the result was the same. I remarked, in deed, that the solution of it in water, which had been thickened to the con istence of syrup, deposited, after some time, small knobs on the sides of the vessel, which had the form of cauli. flowers; the whole solution afterwards coagulated, and appeared like a solid, dry, white mass, full of small cavities, which, when examined with a microscope, seemed to be composed of very small long -crystals, extremely thin, and hardly visible to the naked eye.
VI. Though this manner of crystalysing sufficiently distinguishes the saccharine part of honey from common sugar, I suspected, at first, that this difference proceeded only from the presence of some heterogeneous parts, from which the honey was not sufficiently cleared; but the following experiments evi. -dently shewed, that these two sub. stances differ from each other by properties which are very strongly
honey, while it was upon the fire, produced a very strong efferves. cence, and the mixture immedi. ately became of a dark brown colour, almost back. By continu. ing to add quick lim until the effervescence ceased, h seger of honey was entirel decomposed; the mixture turned quite bi. k, and emitted a smel which was very disagreable, and even nu.
3. The dark coloured solution contains a large quantity of time, which cannot be precipitated by means of aerated alkali, nor by an alkali ren. dered perfectly coustic.
4. If vitriolic acid is made use of to precipitate this lime, it then appears in the form of gypsum; but the remainder of the liquor still contains a very empyreumatic acid, which seems to have a strong analogy with the malic acid of Scheele.
5. If the acid of sugar of honey is treated with nitrous acid, it is con verted into acid of sugar.
6. A much more pure acid may be obtained by making use of a double affinity. For this purpose, it is only necessary to boil together equal parts of honey and quick lime, in a great quantity of water, adding to this solution, which is of a brownish colour, as much charcoal powder as may be requisite to take away the colour entirely. The solution must then be filtered, and to the clear liquor must be added, a very saturated solution of lead in distilled vinegar, until all precipitation has ceased. The precipitate obtained by these means must be washed in such a quantity of water as will edulcorate it thoroughly; after which, as
ach diluted vitriolic acid must be ded as may be sficient to sepate the acid of the honey from the ad: this acid may then be conntrated by evaporation.
7. If the solution of honey and =uick lime is thickened by evapo ation, after its brown colour is aken away by charcoal, a transEarent mass of a light yellow coJur, is produced, which resemles gum arabic; it has a bitter aste, and does not grow moist by being exposed to the air.
8. The clear mass which is produced from a mixture of the acid of honey and lime is perfectly insoluble in spirit of wine; and it may be precipitated from its solution in water by this spirit.
9. Caustic fixed alkalies produce upon honey, and upon the sugar which is procured from it, the same effect as lime. Honey, as well as its sugar, is entirely decomposed by them; and always with a very violent effervescence. The dark coloured extractive mass which is obtained by these means is completely insoluble in spirit of wine; and, when the quantities of the two substances are exactly proportioned, very little taste can be perceived in the mass; that little is by no means alkaline, and can hardly be called saline. This proves that alkalies, as well as quick lime, may be perfectly saturated by the acid contained in honey.
10. Volatile alkali also decomposes honey in the same manner, and with the same circumstances, as other alkalies; but this decom position takes place much more slowly, and only when heat is at the same time made use of.
VII. That constituent part of honey which is got from it by treating it with the spirit of wine (III.)
may be distinguished from the sugar of honey, by the following property, viz. that it cannot be reduced into a dry or solid form. It is owing to this particular part that the solution of honey so readily con tracts a brown colour; for a solu tion of sugar of honey, deprived of this glutinous part, may be thickened upon the fire without suffering any alteration of colour. In other respects, the yellow gluti nous part of honey, here spoken of, shews nearly the same properties as the sugar of honey; and when treated with caustic alkalies, or with quick lime, its taste is also the same.
VIII. The properties which I have above described, are those by which the sugar of honey differs essentially from common sugar. If this last is treated like honey, it exhibits the following results.
1. Neither quick lime nor fixed alkalies produce any decomposition in sugars; no effervescence is observed, nor does the solution shew any change of colour.
2. Whatever quantity of sugar is added to fixed alkalies, they always preserve their causticity; and, even if they are boiled with sugar for a considerable time, they never appear to be united with its acid.
As quick lime, when combined with sugar, is attended with some phænomena which appear not to have been taken notice of by any person, I shall here mention them.
By boiling together equal parts of sugar and quick lime, in a sufficient quantity of water, a solution is obtained, which, by the surpris ing quantity of lime it contains, may be considered as highly saturated lime-water, in which the taste of the sugar is not to be perceived.