280 THE A'A Ti T RE-STl T D V RE I 'IE IV [a : 8-nov., .906 



here that the water set free by the heat soon becomes colored by some 

 other liquid, and that a mass of charcoal remains in the tube afier the 

 water and the combustible gas have been all expelled. It will be 

 found upon trial that this charcoal residue, although it will not burn 

 with a flame like the gas, will slowly burn away with a glow when 

 held by a wire in the flame of the lamp. 



It seems from this experiment that when wood is heated in a closed 

 space, it breaks up into other substances besides charcoal and water. 

 This will explain too, in part, the manufacture of charcoal and wood 

 alcohol by the destructive distillation of wood, that is by heating wood 

 in closed vessels, and the production of coke (carbon) and coal gas 

 from bituminous coal by heating it in closed vessels. 



Let the children char small samples of starch and sugar — try 

 whether they contain water — and whether combustible gases are 

 formed when they are decomposed by heat. The last experiment 

 may be performed by heating a little starch and sugar in an iron 

 spoon until they take fire. It will be seen that the solid substance 

 only glows, but that the flame is a burning gas which rises from the 

 solid matter. The starch and sugar are really being heated in a 

 closed space, shut off from the air by the spoon below, and the burn- 

 ing gas above. In like manner, in the case of wood fire, they can 

 see that the flames are caused by the burning of the combustible 

 gases given off from the hot wood. 



The children will now be able to describe the results of their 

 experiments with sugar and starch, and to state and justify their con- 

 clusions as to the composition of both. They will doubtless conclude 

 that, like wood, starch and sugar are probably composed of charcoal 

 and water chemically united. They may then be told that sugar, 

 starch and wood and several other substances of similar composition 

 are called carbohydrates. The fitness of this name should be shown 

 from its derivation. 



In all this work the teacher is supposed to act only as the director 

 of experiments and as the referee in deciding the validity of the argu- 

 ments and inferences. His skill is measured by the success he has 

 had in inducing each pupil to do his own observing and thinking 

 independently. 



After a careful review of the whole ground, the children should 

 retain a good working idea of chemical union — will see that heat 

 tends to separate substances that have been chemically united — will 

 understand what agricultural lecturers mean by carbohydrates — will 



