ON STUDIES MOST SUITABLE FOR ELEMENTARY SCHOOLS. 517 



contained in food-materials has no value as nourishment, the mineral ash or 

 ' salts ' are needed in the blood and for building up the harder structure of 

 the body. 



The transference of heat ; illustrate conduction, convection, and radiation by 

 the ways in which an oil-lamp or gas-jet loses its heat. Conduction : coat wires 

 of iron and copper with wax, bind the ends tooether and heat the junction ; show 

 that the heat is conveyed more quickly and further along the copper than the iron ; 

 metals generally are good conductors of heat ; wood, glass, water, and air are bad 

 conductors. Some substances in a room feel warm and some cold when touched, 

 though all are at the same temperature. Linen sheets feel colder than calico 

 sheets or a blanket. Wool a bad conductor, chiefly because it contains so much 

 air ; cotton wool. Refer to clothing materials, and the I'act that wool absorbs 

 perspiration and keeps the skin dry ; other domestic application of conductors and 

 insulators of heat. 



Convection : heat carried by heated particles of a liquid or gas moving and 

 communicating their heat to objects with which they come into contact. Revise 

 the lessons on ventilation and circulation of hot water, ocean currents, winds. 

 Radiation : the transferejice of heat energy independently of intervening media. 

 Simple experiments to show that objects exposed to radiant heat of fire or sun are 

 hotter than intervening air. Application of modes of transference of heat to the 

 familiar methods of cooking. 



The effect of surface and colour on radiation and absorption of heat. Black 

 and white clothing materials. Reflection of heat from bright surfaces ; applica- 

 tion to stoves. Modes of heating by closed stoves and open fires ; necessity for 

 carrying away products of combustion. 



The burning of a candle in a closed vessel of air ; disappearance of some air 

 during the burning; nature of residual inactive gas; similar effects when a small 

 lamp burns in a bell-jar over water. 



Pass a slow current of air over bread or carbon heated in a glass tube ; collect 

 and examine the issuing gases with a lighted taper, litmus solution, and lime- 

 water. Notice that the faster air is passed through the tube the more rapidly the 

 carbon burns and the greater the heat produced. 



Inhale and exhale air through lime-water. Collect some jars of breathed air. 

 Test with taper, litmus, and lime-water. Breathing and burning have much the 

 same effect on the air. The body is nearly always hotter than its surroundings ; 

 but in health never varies in temperature. How is this? There must be an 

 internal supply of beat, due to a slow or ' wet ' burning of food-material in the 

 body. Refer again to loss of body heat by evaporation of perspiration on skin and 

 to prevention of loss of heat by clothing. Very simple description of organs of 

 breathing — the lungs, mouth, nose, diaphragm, and rib muscles — importance of 

 deep breathing, fresh air, well-developed and unrestricted breathing apparatus. , 



Metals such as iron, copper, lead, and magnesium, strongly heated in the air, form 

 scales and increase in weight. Air passed over heated metals is inactive, and will 

 not support burning ; this inactive air is not acid, nor will it affect lime-water. 



Phosphorus and sulphur burnt in air produce a diminution in volume of aii', 

 and acid products which dissolve in water ; the residual air is inactive and does 

 not affect lime-water. Determine the proportion of active air by burning 

 phosphorus in a tube. 



Examination of iron rust. Rusted iron is heavier than the iron from which 

 it is formed. Iron will not rust in water free from air. The air affected by 

 rusting iron to the same extent as by burning substances; the residual gas is 

 inactive, is not acid, and does not affect lime-water. 



The active part of air — preparation from red lead and 'oxygen mi.xture'; the 

 properties of active air : the formation of acids when phosphorus, sulphur, and 

 carbon are burnt in it. Hence the name ' oxygen ' ; compounds with oxygen 

 called oxides. 



Air evidently composed of inactive air Cnitrogen) and active air (oxygen) in 

 proportion of about four to one. Oxygen added to inactive air from rusting iron 

 or burning phosphorus forms a mixture similar in properties to air. 



