ON SCIENCE IN SCHOOL CERTIFICATE EXAillNATIONS. 519 



means of red lead and copper scale was heavier than air and more soluble in 

 water than air and a taper would not burn in it. On testing the gas from lime- 

 stone, you find that it resembles the latter gas rather than air. You have also 

 discovered that the gas from limestone can be reconverted into limestone stuff 

 Does the gas prepared from carbon at all resemble it in this respect ? On making 

 the experiment you find it does; indeed you cannot distinguish between the 

 two — they are the same material. Think what a momentous discovery you 

 have made ! That carbon is an important constituent not only of vegetable 

 and animal matter but also of the earth limestone — it seems to be every- 

 where, in some cases in an unburnt, in others in a burnt state. You may ask, 

 how comes it to be in limestone — in a burnt state? What is limestone com- 

 posed of? Chalk, the form which you have examined, consists of the remains 

 of minute shells — shells are of animal origin — are all shells alike in composition ' 

 Such reflections should lead you to study a variety of ishelifi, salt-water, fresh- 

 water and land shells, the shells of birds' eggs. 



In the course of the experiments with limestone, it has been discovered 

 that the gas which is a constituent of limestone stuff is present in minute pro- 

 portion in the air. How does it get there? I'ou know that it is formed by 

 the combustion of coal, wood, &c. As we are kept warm bj- our food and it is 

 probable that it is more or less burnt up in our bodies and that the air we breathe 

 in is used for the purpose, may it not be that the gas is also given out by us ? Try 

 to find out by contrasting ordinary air with expired air. See also if the gas be given 

 off by animals, such as mice, by caterpillars feeding on green leaves, by snails, &c., by 

 keeping these under a bell jar through which air is passed after scrubbing it free from 

 the gas by means of lime. Also endeavour to find out if air be concerned in the 

 germination of seeds by ascertaining if they germinate in air over water and whether 

 the air be affected and also whether as germination takes place the gas be driven off. 



Study of Acids. 



Are you not surprised that you have been able to find out so much — and 

 especially that whatever you do you are always led, sooner or later, to dis- 

 cover something of interest in relation to yourselves ? No doubt you are anxious 

 to continue your inquiries now that you begin to understand what wonderful 

 changes are going on everywhere. 



The gas obtained by burning carbon resembles the product from phosphorus 

 and differs from the earths derived from the metals inasmuch as they are 

 both formed from substances which are clearly not metals — yet as one is a gas 

 and the other a solid they are not directly comparable as are the producte from 

 the metals. Have they any property in common ? Wliat property is character- 

 istic of the phosphorus snow ? Its taste, is it not ? Has the gas an acid 

 taste? Try! Acids stain coloured clothes, do they not? The colours of flowers 

 (ire very sensitive— make coloured solutions from a variety of flowers and see 

 whether they are affected by solutions of the two substances which you are 

 studying and by the common acids. You find that the product from carbon 

 has only a weak action but it seeme to act in the same direction as the acids. 

 Things which are similar may sometimes be substituted for one another, may 

 they not? You know that limestone contains the gas which is derived from 

 carbon and that the common acids in some way turn the gas out — will the 

 acid product from phosphorus have a similar effect ? Try ! You thus discover 

 that the two substances have similar properties, although not alike in strength 

 — both are acidic substances. Are there any other non-metallic combustibles 

 which you can study to ascertain if they yield acidic products? Although 

 sulphur matches are not much used nowadays and almost the only occasion when 

 sulphur is used in the house is when it is put into the dog's water, you perhaps 

 know the smell of burning sulphur. Burn some sulphur, pass the fumes into 

 distilled water; taste the solution, test it with colours and add some chalk to 

 it. You thus become acquainted with a third acidic product of combustion 

 derived from a non-metal : the probability that non-metals form acid com- 

 pounds and metals earths when associated with Fire air is therefore increased. 

 Yeai^s ago, when it became desirable to give significant names to substances, 

 the great French chemist Lavoisier introduced the name oxygen for the gas 



