Fire. Fire is one of the oldest chemical phenomena. Its discovery was one of the greatest boons conferred on mankind, as with it arose sociability, the family joys of the domestic hearth, all industries and arts, together with the wonders they have produced, and still produce from day to day. Hence, we can readily understand how it is that fire has ever been, and still is, among nations the object of a special worship (priests of Baal, Gebers, Hindoos, Brahmans, etc.), and has often figured in the religious or funereal rites of nations most remote from each other, both in time and space, as the Chaldees, Hebrews, Greeks, Romans, Peruvians, Mexicans, etc. But how and when this great discovery was made, in the absence of which we can hardly conceive of the possibility of human arts, or even of human existence, is unknown. Flame. - Flame is gas or vapor, of which the surface, in contact with the atmospheric air, or other supporter of combustion, burns with the emission of light. The luminosity of flame is generally admitted to be caused by the presence of particles of solid matter within, or in immediate contact with, the gas in active combustion. Smoke. Smoke is the product of imperfect combustion, caused either by a want of oxygen or a want of temperature. Bituminous coal contains from 5 to 6 per cent. of hydrogen, which unites with the oxygen necessary to combustion, and constitutes A ton of bituminous coal will make nearly one-third of a ton of water in the form of steam. That this steam is black, does not necessarily indicate the presence of much carbon, as a grain of soot, if distributed evenly in fine particles through a cubic foot of steam, would color it blacker than the ace of spades. Chemical analysis proves the basis of soft coal to be carburetted hydrogen, but it generally contains benzole, naphtha, asphaltum, paraffine, lubricating oil, and a great variety of other substances used in the mechanical arts. Heat. According to the dynamical or mechanical theory, heat is the result of motion among the atoms of matter, or, as it may be otherwise stated, of inter-atomic movement; and this motion is capable of being propagated through space, from one body to another, by undulations of a so-called ether assumed to be everywhere existent in the universe. The relative effect of such heat producing motion, or, in other words, the relative proportions of heat required to cause given effects, may be accurately indicated by numbers, just as if heat were a ponderable agent; and it is usual to speak of heat as if it were an independent material substance: thus, it is said to be evolved, or emitted, radiated, conducted, absorbed, and stored up, or accumulated. As a variable amount of the heat evolved in the combustion of a body is absorbed in the work of effecting alterations in the physical condition of the combustible elements necessary to their effective oxidation, it is impossible to estimate the absolute quantity of heat evolved by the combustion of a body; yet the relative quantities of heat evolved by the combustion of different bodies which may be utilized, can be accurately determined. One of the remarkable effects of the application of heat to matter is, that the same amount will affect equal weights of dissimilar kinds in different degrees. Thus, the amount of heat that will raise 1 lb. of water from 100° to 200° Fah, will raise 30 lbs. of mercury through the same range. The amount that will raise 1 lb. of water 1°, will raise 14 lbs. of air. The capacity of a body for heat is termed its specific heat, and may be defined as the number of units of heat necessary to raise the temperature of 1 lb. of that body 1° Fah. The thermal unit, or unit of heat, as it is termed, is the quantity of heat that will raise 1 lb. of pure water 1° Fah., or from 39° to 40° Fah. The term latent heat means the quantity of heat which has dis appeared from a body, owing to an increase of temperature. The sensible heat is that which is sensible to the touch or measurable by the thermometer. The mechanical equivalent of heat is the amount of work performed by the conversion of one unit of heat into work, and the mechanical theory of heat is based on the assumption that heat and work are mutually convertible. TABLE SHOWING THE NON-CONDUCTING PROPERTIES OF DIFFERENT MATERIALS AT EVEN THICKNESS. Black Slate Sandstone Fire-Brick. Soft Chalk. Oak Wood. Wood and Plaster Sulphate of Lime and Sand Coarse Ashes, Shavings, Hay, and Straw Mineral Wood or Asbestos, cemented. Fine Asbestos, in thread Fine-Powdered Charcoal Ordinary Mineral Wool, Hair-Felt, Cat-Tail, etc. 10-13 8-10 0 Cooling of liquids and solids.-The velocities with which a solid body cools in a liquid are approximately the same, whether it be placed near the surface or near the bottom. It is slightly less when the body is brought immediately under the surface. The nature of the external surface of the cooling body has but little influence. The velocity of cooling increases very considerably for the same body immersed in the same liquid with increasing temperature of the latter. If the cooling power of water be taken at 1, that of alcohol is equal to 0.58; mercury, 2-07; sulphate of copper, 1·03, and common salt, 1:05. Combustion. Combustion is a subject of interest to the engineer, manufac er, and individual, and must ever continue to be so, while the |