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The salicylic acid C, H, 03, and the anisic C, H, 03, are monobasic and contain three equivalents of oxygen; in the first, the deficiency of hydrogen is 14 -- 6=8, and the second = 16 8=8. These acids may then be represented by the formula R- 0
This proportion between the elements of a compound does not, however, necessarily imply a homology; there are some exceptions which depend in some way upon the peculiar grouping of the elements. Thus ordinary ether C, H, O, is represented by the same general formula as alcohol R+2 0, but the chemical characters of the two are entirely different and do not allow us to consider them homologues. It is then necessary to add as a condition of homology, a similarity of chemical characters, dependent upon a like arrangement of the molecules. Vol. i, pp. 29–35.
This notation expresses in a beautiful and simple manner, the relations of homology which exist between different compounds. It is the peculiarity of this system that it is based upon the natural affinities of bodies and not upon analogies; this is the only arrangement which will always be correct, because it is founded in the constitution of the substances themselves.
The important relations which the combustible elements suistain, appear “to permit us to class homologous bodies according to their carbon,” and M. Gerhardt has accordingly constructed upon this basis a classification in which all organic substances are arranged in a tabular form. Those containing the same atomical proportion of carbon constitute a family which is designated by the number of equivalents of that substance. Each family is divided into the carburets of hydrogen and those containing oxygen and nitrogen, so that we have R, RO,, RN, &c. These divisions are found on the left of the table, while at the top are marked at the head of their respective columns, the proportions of hydrogen. This will be better understood by a view of a part of the 1st and 2d families. (Family: Gen formula.
oxalic acid. ICH, R
marsh gas. 1. RO ICH,O,
(CO, oxyd wood-spirit.
bonic acid gas.
By this arrangement we are able at once to give a new substance a place, and to determine its relation to other series of compounds ; those bodies which are homologues are always found in the same vertical column, and hence in looking over the table, we see at once in what families homologues of any particular form exist, and how these may be formed from other bodies of the same family. This may be illustrated by an extensive class of homologous acids of the form RO,, which are here given with their families and formulas. 1. Formic, С
0. 11. 2. Acetic, C H
12. Lauric, C,H,O, 3. Metacetonic, H
0. 4. Butyric, н. 14. Myristic,
H 5. Valerianic, CH
15. 6. Caproic, C. H, 16. Ethalic,
CH 7. Enanthylic, c H
17. Margaric, C, H
02 8. Caprylic, C. H
18. Anamiritic, C,. H 9. Pelargonic, C, H
19. Stearic, CH 10. Capric,
CH,0 The acids of the 1st, 2d, 5th, and 16th families are derived directly from alcohols of the formula R+20; and in the 2d we find aldehyde C, H, 0, a derivative of alcohol, which fixes one equivalent of oxygen to form the acid. Spermaceti in the 16th family has the formula C, H,, 0, and forms ethalic acid by combining with an equivalent of oxygen; it is consequently a homologue of aldehyde. No homologues of alcohol are known in the other families; but in butyral C, H, O, and beeswax C,,H,, 0, we have bodies corresponding to aldehyde, and enanthole and menthol are probably the aldehydes of the 7th and 10th families. We may anticipate that future researches will discover an aldehyde and alcohol for each of these acids, and fill up the 11th and 15th families by a similar series. Four acids of this group have been added to the list within the last two years,* and butyral was but recently discovered as a product of the destructive distillation of butyrate of lime. It will be remembered that ethal, an alcohol, is formed by the action of potash upon spermaceti its corresponding aldehyde. We can thus obtain aldehydes from alcohols and acids, and alcohols from aldehydes.
They are, the metacetonic, discovered by Gottlieb; the enanthylic or azoleic, which was formerly considered as a hibasic acid; and the pelargonic, observed by Redtenbacher among the products of the oxydation of oleic, and supposed to be identical with the acid of the pelurgonium roseum. This occupies the place formerly assigned to the copsic acid of Chevreul, which the observations of Lerch have shown to be a mixture of capric with a new acid, the caprylic.
In this series we observe a regular gradation from the volatile and soluble formic and acetic acids to the solid fatty acids at the other extremity of the scale. Those from the 4th to the 10th inclusive are oily and sparingly soluble, and present a regular increase of about 20° Centigrade in their boiling points; higher in the scale they are solid at the ordinary temperature, and the stearic and margaric cannot be distilled without decomposition. Redtenbacher has recently shown that all the liquid acids of this group, with the exception of the formics, are produced in the oxydation of oleic acid by nitric acid.* Stearic acid by the action of the nitric loses two equivalents of carbon and four of hydrogen in the form of water and carbonic acid; and yields the margaric; which by a farther oxydation affords several of the volatile acids of the series. The other solid acids yield the same results, and are perhaps intermediate products in the oxydation of the margaric by nitric acid.
By the action of nitric acid upon wax, we oxydize a portion of its carbon and hydrogen, and obtain a series of bodies lower in the scale; among these are the succinic, pimelic, and suberic acids, which, as we have already seen, are homologues of the form R-20, Spermaceti yields the same products as wax, but if we expose its homologue of the 2d family, aldehyde, to this process, it cannot yield succinic acid, which belongs to the 4th family, but we obtain instead its homologue in the 2d family, oxalic acid.
The results of science are continually demonstrating the universality of the maxim of Linnæus, Natura non facit saltum. We see bodies possessing the most dissimilar physical characters, but agreeing in constitution, when arranged acccording to their chemical relations exhibiting such a gradation that it is difficult to say where the seeming dissimilarity begins or ends, and we may expect that future discoveries will show many bodies of which but one or two homologues are now known to be members of a complete series.
The examples which we have given, will illustrate the features of this classification; which founded as it is upon the natural affinities of bodies and the numerical relations of their elements, must necessarily be permanent.
(To be continued.)
* This Journal, ii Ser., Vol. iii, No. 8.
I. CHEMISTRY AND Physics.
1. Congelation of Mercury in three seconds, by virtue of the spheroidal state, in an incandescent crucible, (Letter from M. Faraday to Boutigny, Ann. de Chim. et de Phys., xix, May, 1847, p. 383.)—In producing congelation of mercury by virtue of the spheroidal state, I first heated a crucible to redness and maintained it at this temperature ; I then introduced some ether, and then solid carbonic acid ; into this mixture in a spheroidal state, I inserted a metallic capsule containing about 31 grammes of mercury, and in two or three seconds it was solidified. It seemed strange indeed that mercury put into a red hot crucible should come out congealed.
2. On a new Test for Prussic Acid, and on a simple Method of preparing the Sulphocyanid of Ammonium ; by Prof. LIEBIG, (Liebig's Annalen, Jan., 1847; Chem. Gaz., April, 1847.) — When some sulphuret of ammonium and caustic ammonia are added to a concen. trated aqueous solution of prussic acid, and the mixture heated with the addition of pure flowers of sulphur, the prussic acid is converted in a few minutes into sulphocyanid of ammonium. This metamorphosis depends on the circumstance, that the higher sulphurets of am. monium are instantly deprived by the cyanid of ammonium of the excess of sulphur they contain above the monosulphuret; for instance, if a mixture of prussic acid and ammonia be added to the pentasulphuret of ammonium, the solution of which is of a deep yellow color, and the whole gently heated, the sulphuret of ammonium is soon decolorized; and when the clear colorless liquid is evaporated, and the admixture of sulphuret of ammonium expelled, a white saline mass is obtained which dissolves entirely in alcohol. The solution yields, on cooling or evaporation, colorless crystals of pure sulphocyanid of am. monium. Only a small quantity of sulphuret of ammonium is requisite to convert, in the presence of an excess of sulphur, unlimited quantities of cyanid of ammonium into sulphocyanid; because the sulphuret of ammonium, when reduced to the state of monosulphuret, constantly reacquires its powers of dissolving sulphur and transferring it to the cyanid of ammonium. The following proportions will be found to be advantageous :—2 oz. of solution of caustic ammonia of 0.95 spec. grav. are saturated with sulphuretted hydrogen gas; the hydrosulphuret of ammonium thus obtained is mixed with 6 oz. of the same solution of ammonia, and to this mixture 2 oz. of flowers of sulphur are added ; and then the product resulting from the distillation of 6 oz. prussiate of potash, 3 oz. of the hydrate of sulphuric acid, and 18 oz. water. This mixture is digested in the water bath until the sulphur is seen to be no longer altered and the liquid has assumed a yellow color; it is then heated to boiling, and kept at this temperature until the sulphuret of ammonium has been expelled and the liquid has again become colorless. The deposited, or excess of, sulphur is now removed by filtration, and the liquid evaporated to crystallization. In this way from 34 to 34 oz.
of dazzling white dry sulphocyanid of ammonium are obtained, which may be employed as a reagent, and for the same purpose as the sulphocyanid of potassium. Of the 2 oz. of sulphur added, an oz. is left undissolved.
The behavior of the higher sulphurets of ammonium towards prussic acid furnishes an admirable test for this acid. A couple of drops of a prussic acid, which has been diluted with so much water that it no longer gives any certain reaction with salts of iron by the formation of prussian blue, when mixed with a drop of sulphuret of ammonium and heated upon a watch-glass until the mixture is become colorless, yields a liquid containing sulphocyanid of ammonium, which produces with persalts of iron a very deep blood-red color, and with persalts of copper, in the presence of sulphurous acid, a perceptible white precipitate of the sulphocyanid of copper.
3. Separation of Alumina from Oxyd of Iron.-Dr. W. Kuop (Jour. für Prakt. Chem., Oct. 9, 1846,) states that he has effected a complete separation of these two oxyds by precipitating with sulphuret of ammo. nium, washing the precipitate with water containing a little free sulphuret of ammonium, and then extracting the alumina by a solution of potash which also must have a little sulphuret of ammonium in it. In this way the alumina, on subsequent precipitation, is obtained on slow desiccation as a transparent mass, and on quickly drying and calcining it has so perfectly a white color as to leave no doubt of its being extremely pure.
4. Detection of minute traces of Alcohol ; (Monthly Jour. Med. Sci., Dec., 1816.)—Dr. R. D. Thomson proposes in place of the distillation of a liquid suspected to contain alcohol, and trusting to the odor of alcohol in the product, which is the usual mode, to resort to the use of chromic acid, which as is well known, produces a characteristic emerald green solution of oxyd of chromium, in fluids containing alcohol. The characteristic odor of aldehyde given off from the dehydrogenation of the alcohol by the chromic acid, also aids materially in detecting minute quantities of spirits of wine. For this purpose a small quantity of bichromate of potash is placed in the bottom of a conical glass containing a portion of the suspected Auid, and sulphuric acid is poured on it by means of a tube funnel. If alcohol is present, the green oxyd will soon be observed on the surface of the undissolved salt, and the characteristic odor of aldehyde will speedily be perceptible.
5. On the Acid Reaction of the Gastric Juice ; by Prof. C. G. LEH: MANN, (Bericht der Gesellschaft der Wissenschaften in Leipzig, p. 100-105; Chem. Gaz., March, 1847.)-Pelouze, and especially Bernard and Barreswil, have shown with certainty the absence of free muriatic acid in the gastric juice. The author has obtained the same result, and at the same time he has indisputably proved the presence of free lactic acid. To obtain the gastric juice of dogs in the greatest state of purity possible, these animals were kept without food for from twelve to sixteen hours, and then fed from ten to twenty-five minutes before death with bones freed as perfectly as possible from skin and fat. Immediately after they were killed, the stomach was tied at the cardia and pylorus, and removed from the body. It was then opened by an oblique incision near the pylorus, and the Auid poured out, without ihe stomach being at