DR. REIDS RUDIMENTS OF CHEMISTRY.

THE present number of CHAMBERS'S " Educational Course" is a very valuable contribution to Elementary Chemistry ; and if not the most skilfully put together, is the most original treatise of the series that has yet appeared, — as might in- deed be inferred from the subject and circumstances of the publication. Its author, Dr. REID, is a scientific and prac- tical chemist; he is also a lecturer on chemistry, and has been engaged in applying his science to the purposes of life, as in the ventilation of the Houses of Parliament. Hence, the tiny volume before us contains the pith of the thought and experi- ments of many years, instead of the crude results of incomplete and hasty reading undertaken upon the spur of the occasion. Much, if not all of what the Doctor tells, may be familiar to the scientific chemist ; objections may, perhaps, be raised to his plan

of teaching; and it is possible that the deeply learned in the science, which we are not, may detect flaws. But the merits of unity and mastery cannot be denied to the book—it is one and entire : the author is evidently pouring forth his own mind, not doling out shreds and patches of the minds of other people.

And it is only upon such subjects that such books can be ob- tained at such a trivial price. The chemist, the physician, and the professors of other arts, who are paid for individual applica- tions of their knowledge, can afford to write such treatises because they live by their practice, not by their pen. But what man could devote the years of reading and study necessary to write an original "History of the English Language and Literature," (form- ing a previous number of this series,) and be remunerated by the profit of a book which is sold at a price that can little more than ,cover its expenses ?

The object of Dr. REID'S Rudiments is to facilitate the intro- duction of a course of chemistry as an elementary branch of educa- tion. The course is strictly formed upon the method which he has successfully pursued in his own lectures to a great number of classes, of different ages and situations; and, although facilitated by the oral instruction of a master, it contains nothing that can- not be comprehended and practised by a little patience on the part of the self-teacher. The principle of his plan, he says him- self, is to conjoin the study of the practice with the study of the theory : but this must be received with some limitations. We do not perceive any theoretical exposition of the science of chemistry in its fullest extent. The Doctor commences by laying down the axioms, as it were, of the science, and then proceeds to treat of the principal substances on which chemistry is employed; first of all stating the leading principles or rules of the subject, and then illustrating them, or rather directing the pupil to illustrate them, by a number of experiments. Lest this account should not be quite clear, let us give an example. The reader will readily per- ceive the author's merits; which consist in the clearness with which the principles are laid down, the number and interesting nature of the facts that illustrate them, and their novelty and the uses to be derived from them, as well as the weight and fulness of the matter.

COMMUNICATION OF DRAT.

Caloric is communicated by CONDUCTION and RADIATION.

When caloric passes slowly from one portion of matter to another in contact with it, it is said to be conducted, and the process is termed the conduction of

caloric. Metals are the best conductors, then liquids, and lastly gases. Gold, silver, and copper are the best conductors among solids; glass, bricks, and many stony substances, are very bad conductors; and porous, spongy solids, as char- coal, hair, and fur, are the worst.

Put one cud of an iron rod in the fire ; the heat soon passes to it, and along its particles to some distance from the fire. Put a glass tube or piece of wood of the same size as the iron into the same part of the fire; the heat extends a very little way beyond the part touching the fire, both these substances being bad conductors.

Clothing is generally made of bad conductors, that the heat of the body may not be conducted quickly to the surrounding air•. Furnaces, where great beat

is required, arc built with porous bricks, which are very effectual in preventing the escape of heat ; but when a stove is placed in the middle of any apartment, the fuel is surrounded with iron, that the heat may be quickly conducted to the air. The ice in an ice-house is surrounded with blankets or straw to prevent the warm air coming too easily in contact with it.

When heat is applied to the upper portion of any liquid, expansion generally ensues, and it becomes lighter than the rest ; it remains, therefore, resting upon

the colder and heavier part. This may be virally shown by boiling the upper portion of water in a long glass tube, applying heat by a spirit- lamp. IF the heat be applied near the bottom of the tube, the colder portion front above soon sinks below the hot expanded fluid, and pushes it up, so that currents are con- tinually produced, till the whole fluid is beaten to the same point.

Similar movements take place in the air.—See the section upon Carbon, where illustrations will be given of the currents produced in a common fire.

Caloric is said to be radiated when it passes with great velocity from the sun, or from any warm body at the surface of the earth, moving through space or through the air. It is believed in this case to move with the same velocity as light, viz. 192;000 miles in a second. Caloric is also radiated from warm bo- dies that are not luminous, as from the hand or from hot water.

Radiant caloric is absorbed when it falls upon bodies having painted or rough surfaces, such as are presented by bricks and other porous solids, by many kinds of stony matter, and numerous animal and vegetable substances, and elevates their temperature as it is taken up. But brilliant and polished metallic sur- faces absorb little heat; they reflect or turn it back again. Take a piece of common tin-plate, and place it before the fire; it reflects most of the radiant heat. and becomes warmer with extreme slowness. Make the

surface rough with a file or sand-paper, cover it with lamp-black, or black paint; it now absorbs heat quickly when exposed to the file, and soon becomes warm.

Those bodies which are most powerful in receiving radiant heat when it falls upon them, are equally powerful in emitting it when they are warmer than surrounding objects. Thus, a vessel with hot water, having a rough, porous, or painted surface, cools much more quickly than when the surface is brilliantly metallic.

All bodies at the surface of the earth lose heat by radiation in a clear even- ing; they radiate more or less heat, according to the nature of the surface; those that radiate most become colder than the others, and on these more dew

or hoar. frost is deposited, the air coining in contact with them being cooled to the greatest degree, and unable, therefore, to retain all the moisture previously

associated with it. The green leaves of vegetables are powerful in radiating heat, and are accordingly covered with the dew during the night, which is so necessary for plants when there is no rain.

In a cloudy night, as heat does not escape by radiation from the surface of the earth, the temperature never falls so much as in a cloudless sky.

The volume is illustrated, where necessary,by wood-cuts; and some of the subjects handled have an immediate application to the arts of life, as in ventilation.