ON SCIENCE IN SCHOOL CERTIFICATE EXAMINATIONS. 477 



black stulY looks like charcoal. It burns in air or oxygen and forms a gas 

 which turns lime-water milky. But carbon burns in air and forms the same gas. 

 Therefore the black specks are carbon, and the gas from the chalk is composed 

 of carbon and oxygen. We call it carbon dioxide or carbonic acid gas. 



Return to the residue left when all the gas has been driven off by heating 

 chalk. It is a white substance. Try the action of water on it. Is it soluble in 

 water? Shake it up with water filter, and blow air from the lungs into the 

 clear filtrate. It turns milky. It is lime-water. Excursions here into the 

 elaking of quicklime, and the uses of slaked lime. Demonstration of the pre- 

 paration of calcium by the electrolysis of fused calcium chloride. 



Burn some of the calcium obtained in oxygen and prove that the white 

 substance obtained is identical with quicklime. Therefore quicklime is a 

 compound of calcium and oxygen. 



Carbon 



Chalk . .J""" \ Oxygen 



:ldime . . . . Calcmm 



j Gas ,' 



I Quick 



I Oxyg 



:en 



Many objects are suitable for stick courses — e.g., ike candle, common salt, 

 haematite, <kc. 



U. Some teachers prefer to take the work as a problem rather than as 

 subjects. Much of the conventional ' subject ' matter naturally arises when this 

 treatment is adopted, and each suitable occasion for experimental inquiries 

 germane to the general inquiry is taken. Moreover, the manipulation and 

 laboratory practice arise as a necessity in the course of the investigation and 

 the various subjects are correlated. Of course, both these ende should be 

 attained whatever the method employed. But in ' subjects ' there is a strong 

 temptation to take elementary practice as an end in itself ; something to be ' got 

 through.' There are few things more unattractive and dehumanised than such 

 courses, which seem absolutely pointless to the boj-. For example, he does not 

 feel the need of accurate weighing, determination of density, specific gravity, 

 &c., and he has no mental picture of any problem on which such matters bear. 

 When they are not done as ' ends in themselves,' but taken as they occur as 

 necessary machinery in the course of an investigation, their apparent pointlessness 

 disappears, and the boy is at least reconciled to them as necessary evils. 



In ' subject ' courses also so much time is often taken over the laws and 

 their establishment that the applications and machines are never reached 



This result is avoided if the course starts from a machine and is then left to 

 create itself under the direction of the teacher. Suggestion and discussion at 

 the end of a period as to the next thing to ' go for ' result in some questions 

 being simply answered, some discarded by consent for various reasons, whilst 

 others are dealt with experimentally by the boys themselves or by demonstration 

 lectures. 



Thus the properties of water can be investigated as so many geological, 

 biological, chsmical, and physical ' subjects.' Or they can be correlated into 

 one problem course beginning, for instance, with the hydraulic press and then 

 developed as above. Starting from the press, there immediately arise trans- 

 mission of pressure, fluids and solids, principles of machines, work and force. 

 Various pumps follow, leading directly to air pressure and experimental 

 investigation into it by the boys themselves. Barometers, pressure on divers, 

 dams, lock-gates, together with deep-sea sounding, chalk, sand, clay, and 

 Artesian wells provide the humanising element. Flotation follows with Archi- 

 medes' Principle, buoyancy, &c. ; where there is a school bathing-place it is 

 best worked out there practically with a raft, a raft of casks.'-and a weighing 

 machine. 



Sea-water's buoyancy leads on to its properties, solution of solids, crystallisa- 

 tion and solution — all arising out of the problem, instead of as pointless and 

 seemingly useless preliminaries necessary for some future unknown work of 

 which the boy is ignorant. Solution nf air and its influence on fish, &c., lead to 

 Harrogate water, soda-water, sparkling wines, bread or sugar in a lemon squash. 



Carbon dioxide suggests its preparation and properties, respiration, breath- 

 ing, burning, and decay; and so nitrates and manures on the one hand, and 



