1906] Nature Study No. 36. 91 



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 wcod alcohol by the destructive distillation of 

 wood, that is by heating wood in closed vessels, and the pro- 

 duction of coke (carbon) and coal gas from bituminous coal by 

 destructive distillation. 



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 ex- 

 periment 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 does not burn, but 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 burning gas above. In like manner, in 

 the case of wood fire, we see that the flames are caused by the 

 burning cf 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 

 conclusions as to the composition of both. They will doubtless 

 conclude that, like wood, starch and sugar are probably compos- 

 ed cf 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 cf experiments and as the referee in deciding the validity 

 of the arguments 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 car- 

 bohydrates will know that when carbohydrates are heated in 

 a closed place until they decompose they break up into carbon, 

 water, and other substances liquid and gaseous will see that 



