not detailed in the work, his object in doing so being the desire of keeping this first element before the student as long as possible, until the latter shall have fully made its acquaintance by a knowledge of its properties, thus proceeding upon the well established principle, that the mind lays hold of an entirely new subject by slow degrees.

The powers of combination possessed by oxygen are now mentioned, and its compounds with manganese adduced as examples of the union of one body with different proportions of another, as if to break the ground for the reception of the difficult truths relative to combining proportions, and the section is concluded by a numeral representation of the five oxides of manganese, and the three of lead.

The whole is illustrated by eleven wood cuts, representing the apparatus, with the mode of employing it.

I have dwelt more particularly on this first section, that it may serve as a specimen of the remainder, and as I wish to recur to it at the close for the elucidation of a few points, of which I intend to treat.

Hydrogen, and its combination with oxygen, are next introduced, and an experiment arranged to show the composition of water, from which the student obtains an idea of the theory of volumes, and a clearer view of the atomic constitution of bodies.

Nitrogen, and its combinations with oxygen and hydrogen, are mentioned, but not specially treated of, as the former will be found, according to the arrangement adopted by Berzelius, among the acids, the latter with the alkalies.

The peculiar properties of sulphur are now described, and as one of them, its power of crystalizing in certain forms, from which naturally flow observations on the regular forms of bodies. The solid, liquid and vapourous states are exemplified in the body before us, and the section closes with the method of obtaining and purifying it in the large way.

Selenium and phosphorus are slighty noticed, only the combinations of the latter with sulphur and hydrogen being given. Mitscherlich advances the theory that the difference between the two kinds of phosphuretted hydrogen lies merely in a small quantity of phosphorus dissolved by the selfinflammable variety, adducing as an argument the fact that hydrogen in contact with phosphorus for a length of time, takes up a small quantity, causing it to phosphoresce when exposed to the air. According to Rose's analysis, they are chemically the same, and they may be converted into each other by means which we have not as yet wholly in our power. But Mitscherlich's theory does explain how the non-inflammable is sometimes converted into the inflammable variety. It appears to me probable, that the non-inflammable phosphuretted hydrogen is a definite compound, in which the two substances are combined with such force, as not to inflame under common circumstances, but that certain causes operate to decompose it, forming another compound of hydrogen and phosphorus, by which a portion of phosphorus precipitates and is dissolved by the new compound, rendering it phosphorescent by the state of minute division of the phosphorus. The union of oxygen in the air with the dissolved phosphorus produces heat, and this in sufficient quantity, inflames the whole. By the reverse action, the dissolved phosphorus is again taken up into chemical union, and forms the non-inflammable variety, and I think that this is the only way in which we can explain the reconversion of one into the other, and their identity as given by analysis.

Chlorine, with its combinations with nitrogen, sulphur, and phosphorus, bromine, iodine and fluorine, follow in succession. An easy method, unat

tended by danger, of preparing iodide of nitrogen is described, which shows the composition of this class of bodies. A small quantity of nitro-hydrochloric acid is introduced into a test-tube, and a few particles of iodine digested in it at a gentle heat. A part of the oxygen of the nitric combines with hydrogen of the hydro-chloric acid, while the liberated chlorine unites with iodine, forming a brown solution. If ammonia be added to this solu tion, the chlorine of the chloride of iodine unites with the hydrogen of the ammonia, while the iodide of nitrogen precipitates as a dark brown powder. It is filtered, and the paper, while wet, torn into small pieces and dried. The diffusive nature of the remarks on phosphuretted hydrogen, while the sulphuretted is passed over in silence, is excused upon the plea, that "the latter belongs more properly to the acids." I think, however, this gas might have been exhibited to keep up in the student's mind the chain necessary to a clear comprehension of the subject.

A too strict adherence to the rule of describing "all the non-acid metalloidal compounds in this place," brings our author into difficulty, for the introduction of many of them is premature, as regards a majority of those for whom the work was intended, that is, for beginners; and accordingly, after describing cyanogen, we have a full account of the combinations of oxygen, hydrogen and carbon, followed by a description of fifteen compounds of hydrogen and carbon, and these again by the combinations of chlorine, bromine and iodine, with the preceding. The author, as if aware of having committed an error, says, "I have considered it proper to mention a large number of compounds in this place, and enough in relation to each of them to excite some degree of interest," and offering as an apology that the "reader will soon discover that a continued examination of these substances is of the highest importance, inasmuch as it may be the means of enriching the science with many interesting facts." But he does not stop here, for after very properly describing the sulphuret of carbon, we are introduced to certain compounds of oxygen, hydrogen, nitrogen and carbon, viz. to the amids, which close the long section on carbon. There are eighty-four pages devoted to carbon and its compounds, and only seventynine to all previous substances, a circumstance so out of character with the whole tenor of the work, and to the principles which originated it, that we feel ourselves led to inquire into the reason of this deviation. I offer the following very simple solution; first, that this subject, in all its bearings. is at the present moment in the hands of the most distinguished chemists, necessarily giving birth to important facts, which ought to be communicat. ed to the scientific world as soon as possible; and second, that Mitscherlich, with his wonted ability, has himself investigated many of the above compounds, and has deviated from the principles on which the work was com menced, from a desire to make known his discoveries. That this was actually the case, I do not assert, but such are the conclusions to be drawn from a review of the Manual.

A description of borium and silicium closes the first general division of the work, viz. the metalloids and their non-acid mutual combinations.

The remainder of the first part of the first volume is occupied by, first, the general properties of air and the gases, and second, those of water, and collaterally of solid, liquid and aeriform bodies. To gain a just idea of the plan of the whole, it will be necessary to enter a little into detail. The author observes, when introducing the subject, "it appears to me to be more conducive to my end as it certainly would be more intelligible, to bring together in this place what is more general in its nature, and what has been often repeated in the foregoing, after a series of experiments have been

instituted, and many phenomena exhibited." I may however observe that the arrangement is not altogether original with Professor Mitscherlich, it being merely a modification of, perhaps an improvement on, the plan adopted by Berzelius in his large work on chemistry. While the former has neither preface nor introduction, the latter precedes his system by a somewhat cursory notice of light, heat and affinity, and a rather long article on electricity and electro-magnetism. Berzelius follows the metalloids by the general properties of gases and liquids, which subject is considerably expanded by Professor Mitscherlich, as will be seen presently.

A description of the air-pump, followed by the mode of determining the specific gravity of gases, naturally leads to an account of the pressure of the air and its measurer, the barometer. Mariotte's law of compression, and that of expansion are properly here introduced, and we are now prepared to determine the composition of the air by means of hydrogen.

The mixture of gases, and the circulation of oxygen precede an important subject, namely, the examination of substances composed of oxygen, hydrogen and carbon.

I propose hereafter to give a translation of the article on the ultimate analysis of organic substances, which, however, I must remark, I think is rather out of place, in the commencement of a work adapted to instruction.

Flame, the distillation of wood and coal, lamps and furnaces, are next minutely described, and close the general properties of air and the gases. A little reflection will, I think, show us that the greater part of the subject is much more intelligible now, than it could have been previous to the exhibition of the metalloids and their compounds, and though perhaps some of the preceding and following articles might have been omitted with propriety, yet I contend for the superiority of the plan in an elementary work, of first introducing substances, and then the laws by which they are governed in their various actions and relations.

The properties of ice, the specific gravity of solids and liquids, and their relations to heat, are succeeded by a subject on which much of the atomic theory depends, viz; the determination of the specific gravity of vapours; in order to ascertain whether the relation between the specific gravity of the solid and its atomic weight is the same as that between the vapour of that body and its atomic constitution. From the experiments of Mitscherlich and of Dumas, it would seem that from the specific gravity of the solid, we cannot draw conclusions as to that of the vapour; hence we cannot say that if a certain weight of carbon unite with a certain weight of sulphur, then so much of the vapour of carbon will unite with so much of the vapour of sulphur. But the difficulties attending such researches are too. great to allow us to receive the results with implicit faith, and it is therefore advisable to await the confirming experiments of others in this most important of all subjects connected with the atomic theory.

The pressure of vapours, and by an easy transition, the theory of the steam-engine, are next treated of, and the remainder of the volume is occupied by the general relations of solids to solids, of liquids to liquids, and of these to gases, under which we find capillary attraction; solution, with an interesting table to be seen in Professor Beck's work on chemistry; precipitation; filtration; edulcoration; the antiseptic properties of charcoal; condensation of gases by solids and liquids; many of which subjects are treated of in an original manner by Mitscherlich, and it may be advisable to offer them at some future time, in order not to lengthen this essay too much. I now close the analysis of this first part of Mitscherlich's work, and proceed with the inquiry started at the commencement of these remarks.

A close and careful examination of the section on oxygen brings us to a very important conclusion as to the manner in which the science of chemistry may and ought to be taught. That there is at present a deficiency in regard to our elementary instruction in chemistry, every teacher is well aware, and hence in selecting a work for his classes, he chooses "that which is least exceptionable," thus plainly indicating the difficulty with which he has to contend; but so universally is nearly the same plan adopted, that almost every one arrives sooner or later, at the conclusion that "a student, when commencing, should have some previous knowledge of the subject." Now we are not to suppose our readers totally ignorant of numbers, nor destitute of a general elementary education, but we must suppose them ignorant of the peculiar nature of solids, liquids and gases, that there are invisible bodies around us whose properties render them tangible, that all the bodies seen in nature are composed of a few elements. We ought to suppose that they cannot properly distinguish between the metals, earths, or alkalies, and even that they have no definite idea of what a metal is; and yet, aware of this, how few give a course on chemistry, without preceding it by a long series on heat, light and affinity. In describing the conducting powers of solids, can the student fully understand the subject, when many solids are mentioned, which are quite unknown to him? Can he under like circumstances, fully comprehend the doctrine of the capacity for heat, the pressure of vapours, solution, distillation and the like? What does he know of the bodies quoted to illustrate these general laws, and without which they cannot be understood? Much less is he prepared to encounter the theory of flame, the construction of lamps and furnaces, subjects of great importance to every one, though they are necessarily lost, because the terms used in description, the essential terms have not been defined. But the most unaccountable of all seems to be the development at the commencement of a chemical elementary work, of the laws governing the combinations of bodies both by atoms and volumes. In the tables of elective affinity, what does the student know of sulphuric acid, of baryta, strontia, soda, &c. or of a salt, when he is ignorant of its constituents? He no doubt conceives one body to be pulling others with different degrees of force, but it is next to impossible he should have more definite ideas on the subject than this; and yet a reference to our chemical works will show that these doctrines are introduced, and being theoretic, the reasons for and against the theory are usually brought forward and illustrated by a multitude of examples. Experiments are at the same time instituted by way of proof; but I ask, does not this savour of the mystery of the adepts in alchemy, to exhibit a striking effect, and withhold the cause; for what difference is there between withholding the cause altogether, and explaining it in language known to be unintelligible.

But to proceed farther, can a student master the subtle doctrines of affinity, when those more advanced experience some difficulty in reasoning upon them? For example, the first law of Dalton, that "the composition of bodies is fixed and invariable, must be illustrated by a number of well selected facts. Suppose we take sulphuric acid, which is generally brought forward for this purpose. It is an acid; what notion does the beginner form of an acid? When exhibited to him, he conceives it to be something like an oil, which will corrode animal and vegetable matter. To show its bearing on the above law, he is informed that it is always composed (a novel idea to him) of 16 parts by weight, of sulphur, and 40 of oxygen, and that the sulphuric acid formed by the hand of nature ages ago, and that made

artificially at the present day, have precisely the same qualities. With what a multitude of new ideas is he here overwhelmed, that there is an invisible substance, which may be weighed out and made to mingle with a solid, so as to form an acid, in which we cannot detect one of the individual properties of the constituents. It were useless to give more instances, for every one must be struck with the impossibility of rendering a definition intelligible, where the defining terms are not understood, and with the inconsistency of teaching according to this method, while at the same time the instructors must be aware that all their efforts cannot be crowned with success. The remarks made on the first law of combination will apply to the two remaining laws, although the difficulties are increased ten-fold, and I would beg the attention of instructors to this subject; nay, more than this, as our science requires us to "question nature and she will answer us," so I would propose the same principle in this case. Let those interested in the inquiry, experiment for themselves; let them strike out a course founded upon the principle, that "a beginner is wholly unacquainted with the subject," and let them closely observe its effects upon the student, for in this, as well as in other kinds of knowledge, a reflecting and inquiring student often leads us to observations which might otherwise have wholly escaped us, and which may induce important results.

The system adopted by Berzelius, and founded on this principle, was eagerly seized by others, and advantageously extended by Mitscherlich in his Compendium, the commencement of which, the section on oxygen, and a few succeeding, were conceived and executed in a masterly style. He first exhibits an experiment, a fact, and then makes such deductions as naturally flow from it, making the student acquainted with names in connexion with facts. The constant mention of a great number of names, heard for the first time, and without knowing the properties of the substances named, only tends to create a confusion in the mind at the threshold of the science, in the very place where the utmost clearness and precision are requisite. Again, observation teaches us, and it is a received opinion, that we acquire ideas of things before abstract ideas, before we can reason on those things. This is a strong argument in support of my position, but is too generally acknowledged to require amplification.

The whole of Prof. Mitscherlich's Compendium is not conceived with the same energy, and only shows the difficulty of writing with a manifold object in view. For instance, a majority of the compounds described under the article carbon, might have been advantageously deferred to a future. portion of the work; there existed no necessity for such diffuse remarks on the general properties of the solids, liquids, and gases, inasmuch as they break in upon the chain of elementary substances, turning the attention from the principal objects to those of minor importance, at least less so in the commencement. The article on organic analysis is wholly misplaced, and only intended for those much farther advanced in the science. The same might be said of many other portions of the work, which inevitably leads us to the conclusion, that it was written for different classes of hearers, and for different purposes. On this point, I refer to my remarks in the introduction to this paper, where I attempted to show, in a concise manner, that a work on chemistry should possess unity and uniformity of plan, object, and execution. Be this as it may, the present volume of Mitscherlich's Compendium is a valuable addition to the chemist's library.

Philadelphia, May, 1836.