trine, and cellulose are compounds differing from one another in properties, although their composition is of the same elements taken in the same quantities.

n times C6H100, represents each of these three compounds.

What is analysis?

It is the method of separating a body into its component parts and of identifying them.

What is synthesis?

It is the method of combining component parts artificially so as to produce the substance under consideration.

For example, water may be divided into the two substances, oxygen and hydrogen, which compose it; or its composition may be determined by causing these gases to unite and proving that by their union water is actually formed.

An almost limitless number of different substances occur in nature, and are made artificially, in which the same component parts are continually repeated in various modes of union. Upon analysis, bodies are finally obtained so simple that they cannot be analyzed further. These simple substances number about seventy, and are called elements. All other substances, being necessarily made up of combinations of elements, are called compounds.

The following table contains a list of all the elements now known :

What does inorganic chemistry include ?

Inorganic chemistry embraces all the elements and their compounds, excepting those compounds of carbon which are set apart for special reasons given hereafter. The division of the elements into metallic and non-metallic is merely one of convenience.

How is the term "metallic" used?

The term metallic is used as pertaining to those elements having the properties of a metal, viz., lustre, weight, good conductivity of heat and electricity, ductility, malleability, tenacity, opacity, and to such as are electro-positive. This includes about fifty of the known elements.

How is the term "non-metallic" used?

The term non-metallic embraces the rest of the elements, i. e., hydrogen, oxygen, nitrogen (gases at ordinary temperature and pressure); chlorine, bromine, iodine, and fluorine (called the haloid group); sulphur, selenium, and tellurium (called the sulphur group); carbon, phosphorus, arsenic, boron, and silicon.

The line of division is not clearly defined. Some elements, like arsenic, may be fairly put in either class. It is merely a division of convenience, and not fundamentally important.

What does organic chemistry include?

Organic chemistry pertains to the carbon compounds. The division into organic and inorganic chemistry arose from the fact that many of these compounds exist already formed in the bodies of plants and animals.

Organic chemistry is made a special division, not on account of any absolute differences existing between the laws which regulate the formation of substances, but in consequence of the enormous number of compounds of carbon and the peculiar complications so frequently observed in their constitution.

Certain organic substances present a so-called organized structure which is directly and essentially the product of vegetable or animal life, and each, in this respect, varies in its mode of formation and constitution from any inorganic compound. The simple cell, the generator of living organisms, exhibits this organized structure. It is impossible to prepare a cell artificially from its elements; but, on the other hand, many liquid or crystalline organic bodies may be built up from their elementary constituents.

The number of carbon compounds already known far exceeds all the compounds of the other elements taken together, and every day is bringing new ones to light. Nearly all of them are formed by the union of different proportions of carbon with one or more of the three other elements, oxygen, hydrogen, and nitrogen.

In what amounts do the elements occur?

The abundance of the elements varies. Their occurrence on the earth's crust is approximately as follows:

How do the elements vary, and what relation is there between the specific heat and atomic weight of each?

The variation of the elements in their chemical relations is remarkably regular, and seems to be governed by some definite law. If the physical properties of the elements be studied, similar regularities are found; and it is now generally believed, although not as yet fully proved, that all the properties of an element depend in some way upon its atomic weight. For example, the specific heat of an element is inversely proportional to its atomic weight.

Arranging the elements in vertical columns according to the order of their atomic weights, as in the following table, we find that, with the exception of certain metals belonging to the iron and platinum groups, they all arrange themselves in such a manner that the first horizontal line is occupied by the monad elements, the second by the dyads, the third by the triads, etc., as indicated by the composition of the hydrides and oxides in the upper column of the table, where R denotes a metal or hydrogen. Hydrogen itself stands alone, there being no known element intermediate between it and the monad metal lithium. This relation of the elementary bodies, which is called the "periodic law," was first pointed out by Newlands in 1864, and afterwards developed by Odling and Mendelejeff.