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The chemistry of the colouring matters has, perhaps, scarcely as yet met with the extended and complete investigation which the importance of the subject, in a theoretical and practical point of view, appears to deserve. The attention of chemists has been almost exclusively directed to the study of a comparatively small number of these substances, such as indigo, logwood, and the colouring matters of the lichens, which have been well and completely investigated; while the remaining, and by far the more extensive class, has received only a very partial and imperfect examination. To the latter, however, belong some of the most important of our dyes; and among others, the most valuable and indispensable of all, madder namely, the chemistry of which forms a problem as yet very far from being solved, but which chemists have shewn little disposition to submit to a thorough and searching investigation; and this disinclination seems to continue, notwithstanding that ground has been broken on the subject by the important observations of Robiquet, Kuhlmann, Runge, and others, which, though extremely incomplete, serve at least to indicate the importance of the results it is likely to afford, and to clear away the preliminary difficulties by which the commencement of such an investigation is surrounded.

During the last few years, great progress has been made in the study of the organic alkalies, and the discovery of methods by which these substances can be artificially produced, and the long train of investigations by which it has been followed, has greatly extended our previous information, and afforded us some definite ideas regarding their constitution. The advance made has, however, related entirely to the volatile bases produced by artificial processes, and our knowledge of the natural fixed alkaloids stands very much where it did some years since, and is still very imperfect, and in regard to many entirely fragmentary; so much so, indeed, that of all the alkaloids of this class described in chemical works, there are not perhaps a dozen of which the constitution can be considered as definitely fixed, and not half that number of which we know the products of decomposition. The fact is, that the interest attaching to the artificial bases has altogether diverted the attention of chemists from the natural alkalies, which have not hitherto proved a very productive field of inquiry; at least the researches to which many of them were subjected ten or fifteen years since, proved comparatively unfruitful in their results.

The solid compounds of carbon and hydrogen form a class of substances to which chemists have scarcely, as yet, paid that attention which their importance and interest appear to merit. With the exception of naphthaline, very little is known regarding them, and it is remarkable that the numerous and varied products of decomposition obtained from that singular substance should not have induced a more minute examination of the kindred compounds, whose existence has been indicated by different chemists. The interest attaching to these compounds is all the greater because, according to their discoverers, several of them are isomeric, or at least polymeric, with naphthaline; and a more careful examination of them might be expected to throw some light on their intimate constitution, and relations to that body.

The minerals of the zeolite family have for many years attracted the especial attention of men of science, and the class has been rapidly extended in proportion to the progress made in its study in a crystallographic as well as chemical point of view. The first characteristic difference, originally observed long since by Cronstedt, and by him considered to be the distinguishing mark of one single mineral species, which he designated Zeolite,—namely, the property of swelling out by heat previous to fusion,—has since been found to belong to a great number of other combinations. These, although materially different from each other in crystallographic form, have proved to be closely allied in chemical constitution, in so far as they consist, without exception, of a silicate of an alkali or alkaline earth, in combination with a silicate of alumina and water. It is evident, then, that the relation of the silicic acid to the base, in both terms, as well as the quantity of water, is capable of considerable variation, so that the general niineralogical formula which should embrace all the members of the zeolite family would beWhere r represents the monatomic alkaline or earthy basis, and the terms u, t, ,T, y, and z, are capable of varying within certain limits.

Since the year 1803, when Desrone discovered the substance which afterwards received the name of Narcotine, the chemical investigation of opium has engaged the attention of many skilful and distinguished chemists, and in their hands has proved the source of a series of substances, unprecedented in their number and the variety of their properties. Up to the present time, there have been detected in it no less than eleven different substances, one acid, and ten, either basic or indifferent, all presenting definite characters and crystalline form, besides various imperfectly characterised substances, described under the names of caoutchouc of opium, resin of opium, extractive, and the like.

In pursuing the investigation of the crystalline constituents of opium, which formed the subject of a previous communication to this Society, I have succeeded in obtaining from the same mother liquor which formed the raw material of my previous researches, a considerable quantity of papaverine, the base recently detected by Merck, and of meconine, the indifferent crystallizable substance discovered by Couerbe in the year 1830. The former was encountered quite unexpectedly in the precipitate from which narcotine and thebaine were prepared by the process described in the first series of these researches. The latter was only obtained after many fruitless trials, in which I was induced to persevere by the desire of comparing it with the substance discovered by myself among the products of the decomposition of narcotine by nitric acid, and described under the name of opianyl. The composition of that substance, as determined by my analyses, approximates very closely to that of meconine; and though the formula assigned to the former is double that obtained by Couerbe from his analysis of the latter, the sole reason for adopting the higher atomic weight was, that the mode in which opianyl was obtained by the decomposition of narcotine, afforded satisfactory grounds for establishing its true constitution.

Numerous researches have established as a general rule that the products of the decomposition of organic substances vary with the circumstances of the experiment, and the nature of the agents under the influence of which it is performed. If, for instance, we examine the action of heat alone, we find it causing a set of decompositions specially characterised by the evolution of carbonic acid, formed by the union of part of the carbon of the substance with the whole or part of its oxygen; and this action is rendered more definite, and the number of the products circumscribed by all circumstances facilitating the formation of carbonic acid, such as the presence of a base, which will even cause its evolution when heat alone is incapable of producing decomposition. Acids, on the other hand, have a precisely opposite effect, they, in some instances, altogether prevent the formation of carbonic acid, and cause the oxygen to exert its action on the hydrogen of the compound, and to eliminate one or more atoms of water which do not generally exist ready formed in it.

Owing to the great length of time over which the investigation of the products of the destructive distillation of animal substances has stretched, and various circumstances which it is unnecessary to detail, the inquiry has been pursued in a somewhat fragmentary manner, and with less continuity than might have been desired. The difficulties attending many of the experiments, and the occasional exhaustion of materials prepared by laborious processes, extending in many instances over considerable periods, have occasioned long intervals in the regular course of the inquiry which it became necessary to occupy with the examination of such matters as could be taken up at the moment. In this way a number of facts required to complete the history of the bases already described have gradually been accumulated, some of the products of their decomposition examined, and the pyrrol so frequently adverted to in the previous parts of this paper has been subjected to a full investigation. The details of these experiments form the subject of the present communication.

In the fourth part of these researches, I described a new base produced by the action of sodium upon picoline, to which I gave the name of Parapicoline, because it has the same composition as picoline, although the circumstances of its formation appeared to show that it had been produced by the combination of two molecules of that substance, so that its true formula would be C12H14N2. Unfortunately, its high boiling point, and tendency to decompose when distilled, made it impossible to determine its vapour density, which afforded the only means of ascertaining whether this hypothesis was correct; and it was only assumed, because similar cases of polymerisation had been established beyond a doubt in the case of other classes of organic compounds. In the hope of obtaining a similar base of lower boiling point, and therefore better adapted to the necessary experiments, I have submitted pyridine to the action of sodium, and the results of the inquiry are contained in the following pages.

The careful study of the products of destructive distillation has enriched organic chemistry with an extensive series of results of unexpected interest and importance. These results have affected, in no inconsiderable degree, the recent progress of the science; and their influence has been of a twofold character, both general and particular, exerted in the former case in the development of some of the more remarkable general doctrines of organic chemistry; in the latter, in the important light thrown by their investigation on the constitution of the substances from which they are derived, and the facilities they have afforded of following out connections, which the examination of the original substance either does not at all present to our view, or, at least, indicates only in an imperfect or dubious manner. Added to this, we have the remarkable fact of the appearance among these products of substances in some cases identical with those occurring in organised beings; and in others, presenting analogies of the very closest character with the actual products of vital affinity, which, taken together, afford abundant reason for pursuing the investigation of substances which have already afforded results of so remarkable a character.