Technikatörténeti szemle 19. (1992)

KÖNYVISMERTETÉS - Papers of the First „MINERALKONTOR” International Conference on the History of Chemistry and Chemical Industry (Veszprém, 12-16 August, 1991)

close to each other and having different temperatures transmit heat to each other. During this, hotter bodies — receiving less heat rays than the colder ones — cool down while the others are warmed up until the state of equal temperatures is reached. This state of equal temperatures is called the equdibrium of heat, not in the sense that the bodies no longer radiate heat but that each of the bodies in interaction emits the same quantity of heat than it absorbs from that emitted by the rest of bodies. The compensation of temperatures reached in this way is called dynamic equilibrium". 4. About boiling „A11 the changes that take place in the state of bodies by means of heat transmission can be called as the ..operation" of heat and expressed in brief in the following articles a) expansion, b) melting, c) vapour formation, d) chemical decomposition... Every solid, or liquid body can be vapourized... If this change in state takes place on the surface it is called evaporation; if it happens in the bulk as well we talk about boiling". Boiling ..generally happens amongst the following phenomena. First of all, the parts of air existing in the small holes of the liquid are released as small bubbles and move upward, or deposit onto the wall of the vessel. Then, due to the increase of temperature, small steam bubbles are formed which, moving upward, collapse in the colder upper layers of the liquid causing a characteristic bubbling noise that regularly happens prior to boiling... The temperature of liquids does not change during boiling... provided that the other conditions remain unchanged... water heated in a closed vessel can take any temperature over its boiling point, but the vessel containing the water should stand the effective pressure of steam... The Papin pot is based on this property of liquids; this is nothing else but a hermetically closed iron vessel in which water can be heated to even 200°C, and the meat can be cooked tender in a short time by the use of a small amount of combustible; even the bones crumble into jelly and powder in part. It is made safe against bursting away by a release valve loaded with weights". 5. About the flame „The flame is nothing else but a burning flow of combustible particles formed of the heated body and usually directed upward, nevertheless it does not break away from the burning body because the particles burnt and those flying away are continuously replaced by others. Most often the flame has a conical shape... the flame of burning bodies can be coloured if certain materials are appropriately mixed with the burning body, thus the flame of alcohol can be painted red with stroncium salts, yellow with sodium chloride and brick-red with calcium salts. 6. About the temperature of Earth „Our globe can be considered as a heat source itself, because — disregarding its continuously changing surface temperature — we know from experience that it has a constant temperature at a depth of 25 metres which... some 100 feet deeper increases by 1°C. Provided that the temperature inside of the Earth is