tion, when the plant is full of life, though certainly sickening; as this is the cause of the swarm of insects that infect a sick tree. We know that calorie and water contribute to increase the nutriment of mankind, by rendering many vegetable materials innocuous, others digestible in the animal stomach, and it appears particularly efficacious in promoting the saccharine fermentation. Darwin supposes that it could contribute to render manures capable of being absorbed by vegetable roots in a state of less decomposition than by the slow process of putrefaction. But how the process could be shortened I cannot conceive, since the earth suspends every effect. It is certain that the saccharine process, begun in vegetables, will render them more fattening to cattle than when given in their perfect state, especially potatoes; but then great care must be taken that it does not go too far, or they putrefy. And it is not only that the sweetness renders the plants more agreeable to the cattle, who, therefore, eat more of them, but it corrects the acid effects of the rind, and converts it into mucilage. The only deaths which will cut short the process in plants, that I am acquainted with, are those by lightning and frost. In these cases there is no fermentation. The vegetable is killed in a moment, and putrefaction and decomposition immediately succeed; and the curious appearance of plants thus destroyed, clearly exemplifies the dreadful destruction that has ensued. I can perceive no difference in the two; I have often seen potatoes and French beans, when killed by frost, appear in the interior as if stirred with a spoon; the whole is destroyed, the vessels all broken, and the muscles torn to pieces: putrefaction directly succeeds, and the whole is decomposed; and the matter is then drawn by its various affinities to those juices which are of immediate use to the plants which surround the decomposed matter; the water with which it is mixed gives succour to all, and the food is assimilated with the vegetables around. To understand what is the next process (when not directly absorbed by vegetable roots), it would be necessary that the plants be confined, and not mixed with the earth: this would at least show what are the steps which bring them back to mould, to which a part must certainly return. But I have particularly noticed that the vegetables are so far from endeavouring to possess themselves of the putrefied matter, though in great part decomposed, that the roots will often turn from it, till all smell has passed away. Indeed all plants are so susceptible of catching putrefaction, that nature. has undoubtedly guarded against this tendency the plant, therefore, must be completely disorganized before its parts can mix with water, and be absorbed by other roots. How thoroughly then doth this prove that no vegetable can be of use to others till it is completely decomposed; and how plainly does it show the folly of burying young crops, whose crude and watery juices re still more unfit than those of older plants to administer to

their wants. I think I have also proved that as weeds will resuscitate, it is the excess of bad management to put them into the ground again; and as to trees and roots, although they may make manure for the next generation, it is too slow a process for us to expect to derive any advantage from it.

The question of what is the life of a plant, is more difficult to answer. Hunter suggested that the life of an animal might be a subtile and mobile vapour of the electric kind;" and may not this be of the nature of caloric? I have merely shown how the vegetable dies; further I am not competent to judge, especially in so difficult a question. But there appears a great deal of analogy between the death of the more perfect animals, and vegetables, and still more between insects and vegetables; and I still hope that further observations and experiments on the death of plants in my troughs will enable me to penetrate further into this subject. I feel it impossible not to meditate on this topic, and am anxious to obtain the most correct ideas respecting it. An examination into the form of plants has engrossed more than 16 years of my life; and the first cause of their existence must, of course, be a matter of peculiar interest to me. I am, Gentlemen, your obliged humble servant, AGNES IBBETSON.

ARTICLE III.

An Abstract of an Inquiry into the relative Importance of the Crystalline Form and Chemical Composition in determining the Species of Mineral Bodies. By F, S. Beudant.

(From the Annales des Mines.)

CONSIDERABLE disputes have subsisted, upwards of thirty years, among mineralogists and chemists, concerning the principle of classification applicable to mineral bodies. Some mineralogists have adopted the results of chemical analysis, others the crystallographical characters, and others again have united both these in their systems.*. But in thus combining into one system the crystalline form with the chemical composition, a considerable difficulty has arisen from the attempt to decide which of the two characters ought to be regarded as the most essential in the determination of a mineral species.

It is with a view to solve this difficulty that the author has undertaken the present inquiry.

*The illustrious Professor of Freyberg has not founded his classification on external characters alone. It is obvious that he requires the assistance of chemical analysis in the construction of specific characters.

It appears that the first regular classification of minerals on the principle of chemical analysis, was published by Bergman, in 1782, in his "Manuel du Mineralogiste," in which the superiority of this mode of classification over that which had been previously used, was very conspicuous; and it is true that this principle has been since generally adopted in separating the species into varieties.

Since Bergman's treatise, many other systems have appeared, founded more or less upon his principles, and modified according to the existing state of chemical science.

In all these there were found many species of minerals incapable of being otherwise than vaguely defined by chemical distinctions, and the number is continually increasing. Berzelius, however, has very recently proposed a new and more methodical classification, in which he considers the oxides of aluminum, of silicium, &c. as performing the office of acids in the composition of mineral substances. His treatise is unquestionably the most ingenious and perfect of all that have been founded on chemical analysis, and it will doubtless be improved by a more perfect state of chemical science.

In general, in the proposed classification founded on chemical characters, minerals of the same species are defined to consist of such substances as are similarly composed. It cannot be denied, however, that, owing to the irregularity in the proportions of the constituent parts of minerals, this definition becomes uncertain in its application, and the chemical determination of a species will frequently be arbitrary.

About the time that Bergman was employed in constructing his method of classification, Romé Delisle, in comparing together variously formed crystals of the same substance, discovered that they might all be referred to some simple fundamental form, of which they might be considered modifications resulting from the truncation of its edges or angles; but he did not pursue this idea further, so as to apply it to the determination of a species.

M. Haüy at length appeared, and not only multiplied the observations on crystals, but was the first who applied to crystallography the consideration of physical character, combined with the calculations of the geometrician. By a method equally ingenious and exact, he was enabled to demonstrate that all the' crystalline forms were related to one single system of geometry, that this system varied in relation to different substances, but was uniform in its application to all the varieties of the same species; and he thence concluded that crystallization was the character on which the greatest reliance might be placed in the determination of a mineral species.

From this has resulted a new classification, in which a mineral species is defined to be a collection of substances, of which the integrant molecules are similar, and composed of similar elements, and in similar proportions.

It appears, from this definition, that the results of chemical analyses, and those derived from crystallography, are both jointly regarded. But in its application, it will be seen that the author assigns the greatest degree of importance to crystallography; not from any particular predilection for a science which he, as it were, created, but in consequence of a strict examination of each species, and into the degrees of exactitude and constancy, observable in the results both of chemical analysis and of crystallization. This preference given to crystallographical characters has led M. Hauy to separate bodies which chemistry had placed together, and to unite others which chemistry had separated. The same elements, and frequently in nearly similar proportions, being found connected with incompatible crystallization; and on the other hand, elements dissimilar in number and proportion being discovered in uniformly crystallized bodies.

These facts have been shown by M. Hauy, in his Tableau Comparatif; and he hence concludes, that, to determine the true constituent elements of compound bodies, it is required to separate the accidental mixtures from the result of the analysis. But as he does not discover, in the present state of the science of chemistry, a method of distinguishing the essential elements from the accidental mixtures, he conceives that the crystallographical character may be the most constantly and certainly relied upon for the classification of such bodies as chemistry would leave undecided.

These conclusions, which have received the concurrent sanction of many men of science, have nevertheless not been adopted generally; and particular analyses are frequently adduced to establish new species, in opposition to their crystallographical

character.

Chemists agree generally, with M. Haüy, that accidental mixtures enter into the composition of minerals, and that these must be separated before the true component parts can be known; but, they observe, that in many cases it would be necessary to separate one half, or two thirds, of the compound, in order to produce an accordance between the chemical and crystallo graphical characters, and they have considered this proportion too great to be the result of accident. It is to elucidate this circumstance that the following experiments were undertaken.

It is now generally known that the same compound constantly: gives the same crystals; but the inverse of this proposition, which would infer similarity of composition from similarity of form, is true only in theory, or when the compound is perfectly pure. In natural compounds, as well as in those produced in the laboratory, it is frequently contradicted by our experience.

Mineralogists explain these differences of composition by sup posing the addition of accidental mixtures to the constituent elements of bodies, although, from our ignorance of the elements>>

themselves, we cannot determine, with precision, the amount of the extraneous matter.

Chemists, on the contrary, do not admit these accidental compounds on so large a scale.

It appeared to the author that the problem might receive some illustration from a series of experiments on such substances as might be compounded and decomposed at pleasure; as these would enable him to determine the proportion of accidental mixture capable of entering into the composition of a body without affecting its crystalline form.

Mixtures of Sulphate of Copper and Sulphate of Iron.

It had been long known that a mixture of equal parts of sulphate of iron and sulphate of copper would afford rhomboidal crystals similar to those given by sulphate of iron, the diagonals of their faces being to each other as 7 to 10; but this remarkable fact did not determine all the proportions of these two salts capable of producing this rhomboidal crystal. The author's first researches were, therefore, directed to this point.

He mixed sulphates of iron and of copper in various proportions, and produced crystals from the solutions. Equal parts gave, as before, the rhomboidal form; but by increasing the proportion of sulphate of copper, he at length obtained crystals similar in form to those of the sulphate of copper; and by varying the experiments he ascertained the proportions that would give either form.

He at first concluded that the crystals which were produced contained the same proportions of the two salts as the mixture; but by analyzing the crystals* he found the proportions vary according to the degree of concentration of the solution. The sulphate of iron, being the most soluble salt of the two, remained in the greatest proportion in the solution.

Frequently after obtaining crystals of the form of sulphate of iron from some given proportions of the two salts, part of the crystals were re-dissolved, and again crystallized; and by repeating this process, it was found that the proportion of sulphate of iron in the crystals became less and less, and at last was so small that the crystals assumed the form of those of sulphate of copper. Thus crystals which contain 20 parts of sulphate of iron and 80 of sulphate of copper, retained the form of sulphate of iron then being successively redissolved, and again crystallized, were found to retain the same form, although the sulphate of iron was reduced first to 15, then to about 12, and lastly to only 9 per cent., which appears to be the limit of proportions affording the rhomboidal crystal; for on again redissolving and

These crystals were analyzed by dissolving in pure water, and precipitating the iron by pure ammonia; and the proportion of sulphate of iron was computed. according to the analysis of Kirwan, which gives 28 parts of sulphuric acid to 100parts of oxide.