238 REPORT— 1889. 



monstrated experimentally by oxidising finely-divided copper and de- 

 termining the increase in weight, lime being used as drying agent. 

 In this way the characteristics of comjjounds are elucidated. Then the 

 comparison may be made with air and the fact made clear that it be- 

 haves as a mere mixture. Still no reference should be made to elements. 



Problem V. To determine ivhat happens lulien organic suhstances are 

 liurnt. — The experiments thus far made have shown that phosphorus and 

 a number of metals burn in the air because they combine with the oxygen, 

 forming oxides, heat being given out as a consequence ; but that chalk 

 when burnt is split up or decomposed into lime and chalk gas, this result 

 beino- a consequence of the heating alone, the air having nothing to do 

 with it. It remains to ascertain what happens when organic substances 

 ai'e burnt, as these give no visible product beyond a little ashes. As in 

 all cases when vegetable or animal substances are burnt a certain amount 

 of ' char ' is obtained, which then gradually burns away, charcoal or coke 

 is first studied. It having been discovered that the oxygen in air is the 

 active cause of burning in many cases, it appears probable that the air 

 is concerned in the burning of charcoal, coal, &c. As when once set fire 

 to these continue to burn, the charcoal is at once heated in oxygen: 

 it burns, but no visible product is formed ; it therefore follows that if the 

 charcoal is oxidised the oxide must be an invisible gas. How is this to 

 be tested for ? "What gases are already known to the pupil ? How are 

 these distinguished ? Oxygen is excluded. Is it perhaps nitrogen, and 

 is not perhaps the nitrogen in air merely used-up oxygen as it were, pro- 

 duced by the burning of organic substances ? Or is it perhaps that gas 

 which was found in the air along with oxygen and nitrogen, and which 

 turned lime water turbid ? This last being an easy test to apply is at 

 once tried ; the lime water is rendered turbid, and so as to leave no doubt a 

 sufficient amount of the gas is prepared and passed into lime water, and 

 the precipitate is collected : it is found to give off chalk gas when heated, 

 and when the loss it suffers on heating is determined it is found to agree 

 with that suffered by the precipitate prepared from chalk gas. Thus the 

 discovery is made that chalk gas is an oxide of carbon, and that chalk 

 consists of at least three things. 



It may be objected that to make the experiment in this manner takes 

 too much time ; but to this it may be answered that such experiments 

 are precisely similar to those made in actual practice, and that they 

 exercise a most important influence in teaching the pupils to take nothing 

 for granted, never to jump at conclusions, and to rest satisfied if they 

 progress surely, however slow the advance may be. 



The char from a number of organic substances may now be burnt in 

 oxygen, and the gas passed into lime water ; chalk gas is found in every 

 case to be a product, and hence the presence of a common constituent- 

 carbon — in all is established. In burning substances such as sugar, it is 

 scarcely possible to avoid noticing the formation of a liquid product, so it 

 is evident that chalk gas is not the only product of their combustion, or 

 carbon their only constituent. 



Food materials generally having been found to contain ' carbon,' as 

 they are obviously in some way destroyed within the body, and it is 

 known that air is necessary for life, the question arises, what becomes of 

 food, and why is air necessary for life ? Is the food, perhaps, in large 

 part ' burnt up ' within the body, thus accounting for the fact that our 

 bodies are always warm ? The characteristic product of combustion of 



