INTRODUCTION.

THE Common life of man is full of wonders, Chemical and Physiological. Most of us pass through this life without seeing or being sensible of them, though every day our existence and our comforts ought to recall them to our minds. One main cause of this is, that our schools tell us nothing about them-do not teach those parts of modern learning which would fit us for seeing them. What most concerns the things that daily occupy our attention and cares, are in early life almost sedulously kept from our knowledge. Those who learn any thing regarding them, must subsequently teach themselves through the help of the press: hence the necessity for a Popular Chemical Literature.

It is with a view to meet this want of the Public, and at the same time to supply a Manual for the Schools, that the present Work has been projected. It treats, in what appears to be their natural order,

of THE AIR WE BREATHE and THE WATER WE DRINK, in their relations to human life and health-THE SOIL WE CULTIVATE and THE PLANT WE REAR, as the sources from which the chief sustenance of all life is obtained-THE BREAD WE EAT and THE BEEF WE COOK, as the representatives of the two grand divisons of human food—THE BEVERAGES WE INFUSE, from which so much of the comfort of modern life, both savage and civilised, is derived-THE SWEETS WE EXTRACT, the history of which presents so striking an illustration of the economical value of chemical scienceTHE LIQUORS WE FERMENT, so different from the sweets in their action on the system, and yet so closely connected with them in chemical history— THE NARCOTICS WE INDULGE IN, as presenting us with an aspect of the human constitution which, both chemically and physiologically, is more mysterious and wonderful than any other we are yet acquainted with-THE ODOURS WE ENJOY, and THE SMELLS WE DISLIKE; the former because of the beautiful illustration they present of the recent progress of organic chemistry in its relations to the comforts of common life, and the latter because of their intimate connection with our most important sanitary arrangements— WHAT WE BREATHE FOR and WHY WE DIGEST, as relating to functions of the body at once the most important

to life, and the most purely chemical in their natureTHE BODY WE CHERISH, as presenting many striking phenomena, and performing many interesting chemical functions not touched upon in the discussion of the preceding topics-and lastly, the CIRCULATION OF MATTER, as exhibiting in one view the end, purpose, and method of all the changes in the natural body, in organic nature, and in the mineral kingdom, which are connected with and determine the existence of life.

It has been the object of the Author in this Work, to exhibit the present condition of chemical knowledge, and of matured scientific opinion upon the subjects to which it is devoted. The reader will not be surprised, therefore, should he find in it some things which differ from what is to be found in other popular works already in his hands or on the shelves of his library.

CHAPTER I.

THE AIR WE BREATHE.

Height of the earth's atmosphere; it is one of the elements of the ancients.-Composition of the atmosphere.-Oxygen, preparation and properties of-Nitrogen, preparation and properties of.-Proportions of these elements in the air; their adaptation in kind and quantity to the existing condition of things.-Uses of the oxygen and nitrogen.-Uses of the carbonic acid; its importance to vegetable life.-Deleterious influence upon animal life.-The "Poison Valley" of Java.-Importance of the watery vapour of the air; its constant circulation.-Formation of rain and dew; their many uses.-Accidental constituents of the air; ozone, nitric acid, and ammonia-Vapours which rise from the surface of the earth, and saline matters from the sea.

THE earth we inhabit is surrounded by an atmosphere of air, the height of which is known to be at least forty-five miles. It presses upon the earth with a weight equal at the level of the sea to about 15 lb. on every square inch of surface. As we ascend high mountains, this weight becomes less; and as we go down into deep mines, it becomes sensibly greater.

We breathe this atmospheric air, and without it we could not live a single moment. It floats around the earth in almost perpetual motion; and according to the swiftness with which it moves, it produces gentle breezes, swift winds, or terrible tornadoes.

Though very familiar to us, and regarded with little