CHEMISTRY. All the changes that take place in bodies,—whether by the operation of powers not under the di rection of man, which are called natural phenomena ; or of the same powers, mo dified in their direction by the exercise of our voluntary exertions, which con stitute the processes of art,—arc effected by motion. When the bodies from their size and distance from each other can be separately distinguished by our senses, the effects are referred to the division of philosophical science called mechanics : but when the minuteness of the bodies themselves, and of the spaces to which the individual actions are confined, are such that we cannot view and contem plate them separately, but are under the necessity of inferring the nature and causes of their motions from general re sults or phenomena, the changes are re ferrable to chemistry.
Chemistry, therefore, as a science, teaches us to estimate and account for the changes produced in bodies by motions of their parts, which are too minute to affect the senses individually : as an art, its practice 'Consists in placing or apply ing bodies, with regard to each other, in such situations as are adapted to produce those changes.
In our investigation of the results of chemistry, we find ourselves, from the regular connection of the facts, enabled to forte! what will happen to certain bo dies in certain circumstances; and the rules by which, from experience, we are capable of doing so, are called laws of nature, if they relate to bodies in gene ral; but when they relate to particular descriptions of bodies, we form our ex pressions so as to refer the effects to the bodies themselves, under the name of qualities or properties. The discovery of these laws and properties must, in the first instances, be effected from the ob. servation of natural events, and after wards by instituting experiments for the express purpose of manifesting them. In these experiments we may either sepa rate compounded bodies into their sim pler parts, which is called analysis ; or we may unite simple parts so as to form a compound body, which is called syn thesis. And our reasonings concerning these facts will have a correspondent de nomination. When we describe and ex plain the process of analysis, by which general results are deduced by separat ing effects from each other, the opera tion of the mind is distinguished by the same name ; but when, from the general results, we show in what manner particu lar events are produced by combining bodies together, the method is distin guished by the term synthesis.
The synthetical method of teaching is undoubtedly the most luminous and clear, where the first principles or simple elements of our knowledge are known or admitted, as is the case in geometry. But in chemistry this method of teaching cannot, from our imperfect knowledge of the facts, be generally adopted, with out admitting the simplicity of a variety of substances, concerning which there is just reason to doubt.
It is true, indeed, that such admissions are generally made with a previous notice or reservation of this uncertainty. But by the constant use of the supposed facts, along with others which are better estab lished, the mind becomes habituated to mix hypothesis with facts ; and the ima ginary beauty of connected science must from time to time be destroyed by the ap pearance of new truths. The revolutions of chemical science have amply shown this ; and the numerous imperfections which still remain, have left considerable latitude for the arrangement'of materials in a system of chemistry. If the theory were in its commencement, a treatise on chemistry would be little more than a collection of receipts for processes; and even in the present state of the science, different authors of credit and respecta bility greatly differ in the disposal of their subjects. Operitive chemistry usually precedes the theory in the ear lier works. Some writers treat of com pound bodies, and deduce their princi ples or component parts in the way of analysis : while others begin with the habitudes or powers by which the seve ral changes are effected. But it must be confessed, nowithstanding the magni tude of the discoveries which have been really made, and the elevated preten sions of a few theorists, that the practical science is still in its infancy. Every one of the phenomena is sufficiently compli cated as to be referrible to various topics of consideration; and to which of these in a general way our attention shall be first directed, is in many cases a matter of indifference. It appears to us that the advantages of treating the subjects in a popular way, by first attending to the general properties and habitudes of bo dies, and the methods of operating upon them, and from thence proceeding the different classes of bodies, are such as entitle this method to a preference before other arrangements, which afford a greater appearance of synthetical or der.