the bromine he manufactures into this compound, by mixing bromide of potassium, alcohol, and sulphuric acid, and then distilling. The bromine can be readily reproduced from this compound.

IODINE.

In the manufacture of this substance there are small improvements made from time to time. Messrs. Cournerie formerly conducted all their evaporations over the naked fire; they now carry them on by means of steam, and consider that they have economized the production of this important substance.

M. Moride, who carries on extensive operations on the island of Noirmoutiers, burns a portion only of the sea-weed; the remainder is stretched about the fire and carbonized. This carbon is leached, and the residue is mixed with turf and used as fuel. The inhabitants conduct this operation of carbonization, and sell the material to the manufacturer. In this way 2,000 bushels of this carbon are produced weekly.

The lixiviated solution is concentrated by steam, and the mother water produced, after separating the bulk of the salts, is treated with sulphuric acid strongly nitrous, and the iodine is precipitated. Coal naphtha (boiling at about 1200 C.) is now added, and the mixture is agitated, when the naphtha takes up the iodine. This last is now agitated with a solution of soda, and the iodine is separated from the naphtha, which is ready for another operation, as the naphtha does not now contain iodine. Recently much attention has been drawn to the soda-nitre beds of Peru as a source of iodine, it having been shown, more than ten years ago, that the iodine existing in the mixture was in the form of an iodate. The iodine is obtained by pouring a solution of sulphurous acid or the bisulphite of soda into the mother waters, which precipitates the iodine as a black powder. When the exact proportion of reagents is employed, if there be an excess, the iodide is formed and the iodine is lost; if not enough, the iodate is not decomposed, and is also a loss.

The mining company of Tarapaca produces 200 tons of nitre, and an equal quantity of mother water containing one two-thousandths of iodine. This company, by imperfect treatment, extract only eighty-five pounds of iodine daily. Other works are now looking also to the production of iodine, and when the manipulations are improved a very much larger quantity will be produced; and as these nitre beds will furnish nitre for a great number of years, this source of iodine is important, and deserves careful consideration.

CHAPTER VII.

MANUFACTURE OF ILLUMINATING GAS FROM COAL, AND THE UTILIZATION OF THE WASTE PRODUCTS.

COAL, AND ITS EFFECT UPON THE DEVELOPMENT OF THE ARTS—MANUFACTURE OF GAS; IMPORTANCE AND EFFECTS-MATERIALS USED--RETORTS AND FURNACES-GAS CONDUCTORS AND CONDENSERS-METHOD OF HEATING THE RETORTS-DISTRIBUTING PIPES EXHAUSTERS-GAS METERS-GAS BURNERS-COLLATERAL USES OF GAS-PORTABLE GAS WORKS-NEW FORMS OF ILLUMINATING GAS-THE CHEMISTRY OF GASMAKING THE GAS WORKS OF PARIS-UTILIZATION OF THE WASTE PRODUCTS OF THE MANUFACTURE OF COAL GAS-COKE—AMMONIACAL LIQUORS-COAL TAR, ITS COMPOUNDS SPENT OXIDE OF IRON-REFUSE LIME-ABSORBENTS OF AMMONIA-COAL TAR COLORS-VIOLET COLORS-ANILINE REDS, BLUES, GREENS, AND OTHER COLORS— THEORY OF THE FORMATION OF COLORS-CARBOLIC ACID COLORS-NAPHTHALINE COLORS.

INTRODUCTION.

There is not any substance which, in the last forty or fifty years, has produced such wonderful results in the development of the arts, commerce, and industrial pursuits, as coal. It is not, however, our province here to refer to its applications in metallurgy and the other arts in which direct operation brings about the required results; but to confine this and the following chapter to the industrial products obtained from coal by operations more or less indirect.

I had drawn up a report based on the results as exhibited in Paris in 1867, but it was so extended and hastily digested that it has been discarded, and in its stead I have combined my report on gas and gas materials, as made out for the jury reports published by the Imperial Commission, with the admirable lectures of Dr. Letheby on the articles made from coal, and have appended an extract from the report of Dr. Hofmann.

GAS AND GAS MATERIAL.

PROGRESS OF THE ART OF GAS-MAKING.

Important progress has been realized in the manufacture of gas-more, however, in reference to giving stability, and to perfecting apparatus already employed, than in the discovery or application of anything new. The importance of this industry is manifesting itself every day, not so much in the direct products for illuminating purposes, already so well established, but from the great number of valuable and beautiful products resulting from the treatment of the residues by the chemist.

We have become so accustomed to the use and production of illuminating gas from coal that, like most things we are habituated to, the

great value of the product and the importance of the industry, as well as everything else connected with it, is lost sight of alongside of more glaring and recent discoveries of far less magnitude; yet if we review the origin and development of this industry, and the direct and indirect effects of it upon the advancement of the age, it is certainly to be ranked as one of the most important inventions of the present century, and second only to that of the steam-engine.

Its direct effect is to convert night into day, to make the short and obscure winter days equal to those of summer, giving more time to those occupied with in-door pursuits, and enabling them to conduct their labors with less fatigue to the eye and with more certainty of execution. In this aspect alone the immense wealth that has been added to the industrial arts is incalculable.

In its indirect effects, the use of coal gas has benefited society by saving vast tracts of land for other agricultural purposes that would have to be devoted to the cultivation of plants furnishing oil and fatty matters to be used for illumination; and besides, there have been saved for other purposes hundreds of ships and thousands of seamen that would be required for the whale and other fisheries carried on simply for the purpose of procuring oily matter to be used for furnishing light.

Regarded as a luxury, its benefits are not to be despised, for it has cheapened many of them to such a degree that both rich and poor are equal participants of them. Our brilliantly lighted streets are evidence of this fact, so that the people traverse our cities with the same ease and security at night as in daytime. And here we may again allude to another fact in connection with the manufacture of coal gas, namely, that the offensive residues which are the natural result of gas making have been made to give rise to most important industrial pursuits, employing a large amount of capital and accumulating wealth. Coke, ammonia, pitch, and tar have been for many years drawn from this source; but it has been left for the more recent developments of chemistry to extract from the tar, by processes more or less indirect, beautiful crystallized compounds used in giving to silk, woolen and cofton, colors that rival in brilliancy the hues of the rainbow; and this discovery in its turn reacts on the manufactures of the various textile fabrics. All of these facts will be most fully developed in the report on coal colors, by Professor Hofmann, to whom we are indebted for the first and most important steps in their manufacture.

It is not the design or province of this report to go into the historical details of the origin and development of this industry. Like many other great discoveries, the world was prepared and looking for it. The minds of many were occupied with it, and the distinguished Scotch philosopher, Dr. Chalmers," at a time when the streets and lanes of all great cities were lighted with oil burnt in lamps, held that the time was not distant when a carburetted-hydrogen gas would be substituted instead, and on getting his house repaired he actually introduced into the walls of the

house a system of tubes and pipes for the passage into the various rooms of the gaseous fluid yet to be employed as the illuminating agent." among all the vague speculations and ingenious devices, there were two individuals endowed with skill and practical minds, who were giving shape and form to them-Murdock in England, and Le Bon in France. The combination, however, of circumstances favored the former, and I think no impartial investigator of the subject will fail to render to William Murdock, of Redruth, Cornwall, the sole merit of the practical application of coal gas to the purpose of artificial illumination, in about 1800. And it is a noteworthy fact that this discovery was first exhibited publicly as a rejoicing over the hush of war and the renewal of peace, on the occasion of the grand illumination in England commemorative of the peace of Amiens, in 1802.

Since the commencement of the century to the present time the industry of coal gas has been gradually improved, and the mixed nature of this compound has been more and more simplified, rendering the illuminating gas better adapted for the purposes to which it is applied; the condensable products and impurities are better removed, and the latter, in their turn, made to subserve some useful purpose, until the gas manufacturer receives the coal from the mines and sends forth nothing that is useless.

In a systematic review of the gas industry and products resulting therefrom, so far as regards its more recent improvements exemplified by the great Exposition of 1867, the remarks will be confined especially to what was there exhibited.

MATERIALS USED FOR MAKING ILLUMINATING GAS.

The Exhibition does not furnish anything new under this head. To sum up what is now known can be done in a few words.

The materials now used in the manufacture of gas may be comprised under the following articles: coal, wood, pitch, rosin, oils, fats, and petroleum. There are also other vegetable and animal products which have been suggested, and even employed, on a small scale, as bones, &c. But of all the raw materials there are none which can compete with coal, except under some extraordinary combination of circumstances; for not only does coal furnish gas more 'economically, but it affords valuable residues, producing the fuel necessary for its formation in much larger quantity than is required for that purpose, and other important refuse matter, as tar, ammonia, &c. The question in regard to the substitution of petroleum for coal is not worth serious consideration at the present time. It may be advantageous occasionally to add, in a convenient manner, some petroleum when this is abundant and the coal used requires the addition of a material to furnish gas of a high illuminating power; then from twenty to thirty gallons of petroleum to 2,000 pounds of coal may become desirable. Pitch and rosin, when cheap, may be added to coal for the same purpose. All other adjuncts, as vapor of water, &c., serve

only to dilute the gas and make it of less value. Bituminous coal, under its various forms, has not found a rival, nor is it likely to encounter any for a long time.

The following fact may be mentioned in connection with the manufacture of gas from wood. In those countries where this material is abundant and coal is not accessible, wood, aided by the addition of some substance furnishing a rich hydro-carbon, may be made to furnish a very useful illuminating gas, and an economical one, especially when the residue in the retorts and the material distilled with the gas can be rendered serviceable. In Coburg, Canada, it is said to have been used advantageously, furnishing a good gas and a valuable residue, viz:

Two parts pine wood.

One part hard wood.
One part bones.

The residue in the retorts is an excellent charcoal for bleaching purposes, and the other residues are quite serviceable. Where bones cannot be obtained, offal and other coarse animal matter can be used to mix with the wood. This suggestion is worthy of consideration, especially for many small towns peculiarly situated.

RETORTS AND FURNACES.

These are the first and most essential parts connected with gas-making; and the present Exposition is rich in specimens of these from various countries. In the Belgian department, we have the fire-brick, tiles, and retorts from "La Société anonyme des terres plastiques et produits refractaires d'Andennes," a company employing nearly 20,000 tons of clay annually, requiring about two hundred and twenty men, and having thirty-two large kilns. Among the articles exhibited by this company are very large retorts, one of which is over ten feet in length and two feet across, with an opening of about seventeen inches, and two inches thick; it weighs about 1,700 pounds, and is of most excellent manufacture, which is equally true of all other articles exposed by the company. Near the above are to be found the retorts of Sugg & Co., of Ghent, who supply, to a very large extent, the gas works of Germany. From Prussia there are excellent products of fire clay, made by Vygen & Co., of Duisburg, and used in Germany, Holland, and Switzerland. England is represented by the well-known products of Cliff & Son.

France furnishes retorts and gas ovens of excellent quality; there are several exhibitors, but none are so conspicuous as those from Bosquet & Co., Lyons, and from the Paris gas company. The retorts from the former establishment are covered with a kind of black enamel, and are set in the gas ovens by being simply supported at the two ends. Without further investigation, I should doubt the advantage of this style of setting; its simplicity may be too great a sacrifice to its security.