230 



NA TURE 



[Jan. 8, 1885 



2. Show the production of carbon dioxide by the oxidation 

 of ordinary articles of food, as by heating small quantities of the 

 dried substance, such as sugar, bread, or meat, with copper 

 oxide. 



3. Show that carbon dioxide exists in the air by pouring clear 

 lime-water into a shallow vessel exposed to air, and explain that 

 this small quantity of carbon dioxide serves as the main food of 

 the plants that grow on the earth. 



4. Expel air from water by boiling, and explain how fish and 

 aquatic plants are thus provided with oxygen and carbonic acid. 



5. Explain that plants eliminate and animals require oxygen. 

 That animals take in oxygen from the air, and give out carbonic 

 acid. That plants possess the power under the influence of light 

 of assimilating carbon from carbon dioxide and liberating the 

 oxygen. Explain that thus the balance of oxygen and carbon 

 dioxide in the atmosphere is maintained. 



6. Illustrate the action of plants by the formation of bubbles 

 of oxygen when a fresh plant is exposed to the action of light in 

 water containing carbonic acid in solution. 



IV.— Water 



1. Illustrate the three states of matter, the solid, the liquid, 

 and the gaseous, with ice, water, and steam, and point out that 

 the difference is caused by increase or diminution in the amount 

 of heat present. 



2. Composition of water. Decompose water by the electric 

 current. Collect the two gases separately in a voltameter, and 

 exhibit their properties. 



3. Show formation of water by explosion of a mixture of 

 hydrogen (two volumes) and oxygen (one volume) in a soda- 

 water bottle. 



4. Explode soap-bubbles inflated by a mixture of hydrogen 

 and oxygen in the above proportions. 



5. Throw potassium or sodium into water, and collect the 

 hydrogen. 



6. Pass steam over red-hot iron, collect the gas and show that 

 it is hydrogen. 



7. Show that the same gas may be obtained by dissolving zinc 

 clippings or iron turnings in dilute sulphuric acid. 



8. Demonstrate the properties of hydrogen : 



(a) Its combustibility. 

 (A) lis lightness. 



(c) That a candle will not burn in it. 



(d) That water is formed when it burns in air. 



9. Compusition of water. Pass oxygen over red-hot copper, 

 and show by weighing before and after that the weight increases. 



10. Pass hydrogen over the copper oxide thus produced, heat- 

 ing gently. Collect the water, and show that the copper oxide 

 has been entirely reduced, the tube weighing the same as before 

 passing the oxygen through it. 



11. Determine the composition of water by weight by passing 

 dry hydrogen over half an ounce of copper oxide, and collecting 

 the water in a weighed chloride of calcium tube. Show approxi- 

 mately that water contains two parts by weight of hydrogen to 

 sixteen parts by weight of oxygen. 



12. Note the first law of chemical combination : that chemical 

 compounds, such as water, always contain their components in 

 the same unvarying proportions. 



13. Contrast the properties of water with those of its con- 

 stituents on the one hind, and the properties of air with those 

 of its constituents on the other. 



14. Call attention to air and water as illustrations of the dif- 

 ference between a mixture and a compound, and quote oxygen, 

 nitrogen, and hydrogen as examples of elementary bodies. 



'5; Separation of impurities from water by filtration and dis- 

 tillation. Preparation of fresh water from salt water. 



16. Experiments illustrating solution and crystallisation. 

 Soluble substances, as sugar, washing soda, alum ; slightly 

 soluble substances, as gypsum or plaster of Paris ; insoluble sub- 

 stances, as chalk, flint, and sand. 



17. Crystallise carbonate of soda, and sulphate of copper. 



V. — Oxygen and Ozone 



1. Prepare oxygen by heating 



(a) Oxide of mercury. 



(b) Potassium chlorate. 



(c) Mixture of potassium chlorate, and either manganese 



dioxide, copper oxide, or ferric oxide. 



2. Show the re-ignition of a splinter of red-hot wood and 

 glowing wick of taper. 



3. Burn charcoal in oxygen, and show the formation of carbon 

 dioxide. 



4. Burn phosphorus simultaneously in air and in oxygen. 



5. Burn watch-spring in oxygen. 



6. Show that iron does not rust in dry oxygen. 



7. Ozone. — Describe and demonstrate the formation 1 f ozone 

 by submitting oxygen to the silent electric discharge. 



8. Describe and demonstrate the properties of ozone which 

 distinguish it from ordinary oxygen, such as its action on metallic 

 mercury, on indigo solution, or on potassium iodide and starch. 

 Also its change to ordinary oxygen when passed through a 

 heated glass tube. 



9. Explain the difference in density between oxygen and 

 ozone. 



VI. — Combining Wtights ; Names and Symbols of the Elements : 

 Chemical Calculations, dVf. 



1. Exhibit list of the elements, distinguishing (by means of 

 the type) the non-metals from the metals ; and, again, the more 

 commonly occurring metals from those which are rarer. 



2. Describe the occurrence of these elements in the air, in the 

 sea, and in the solid crust of the earth. 



3. Write up the results of the quantitative analysis of potassium 

 chlorate. Explain that this is the result of experiment, and 

 demonstrate the fact that, when heated, an unalterable weight 

 of oxygen is given off and a given unalterable weight of potas- 

 sium chloride remains behind. 



4. Dissolve a crystal of pure chlorate of potassium, and the 

 residue of chloride from heating chlorate, in two separate 

 glasses, and show the difference in the reaction with silver 

 chloride. 



5. Explain the meaning of the term chemical symbol, and 

 chemical formula of the salt, referring afterwards to the com- 

 bining weights of the elements. 



6. Explain the mode of determining the formula from the per- 

 centage composition. 



7. Method of calculating the quantity of oxygen from potas- 

 sium chlorate (and from manganese dioxide). 



VII. — Acids, Bases, and Salts 



1. Burn sodium in oxygen ; dissolve the product in water ; 

 give the formula of the oxide. Express the action of water upon 

 it by an equation. 



2. Act on water with sodium, and collect the hydrogen. Ex- 

 plain by equation that the same substance, sodium hydrate or 

 hyclroxide, or caustic soda, is formed, as in experiment 1. 



3. Burn sulphur in a current of oxygen, and show the product 

 fumes slightly in the air. Explain that it is a mixture of 

 sulphur dioxide and trioxide. Pass the gas thus obtained into 

 water. 



4. Add litmus solution to the solutions obtained in experi- 

 ments 2 and 3, and show that on adding the one solution to the 

 other the colour is changed, or a point is reached where a further 

 addition of the one has no effect, whereas a minute addition of 

 the other at once changes the colour. Explain the action by an 

 equation. 



5. Explain that the compound formed from the sodium oxide 

 and water is termed an alkali, or alkaline or basic hydroxide, 

 and the oxide from which it is formed an alkaline or basic oxide ; 

 that the compound formed from the sulphur dioxide and water 

 is termed an acid hydroxide or acid, and the original oxide an 

 acid forming oxide or anhydride. 



6. Explain that sodium hydroxide and sulphurous acid may be 

 taken as representative of the two classes into which hydroxides 

 are divided. 



7. Explain that by the action of the one upon the other a salt 

 is formed. Exhibit a white crystalline salt, e.g. sodium sulphate. 



VIII. — Hydro, en 



1. Prepare hydrogen by the action of dilute sulphuric acid on 

 ^inc. 



2. Show that it is not obtained by the use of pure zinc (amal- 

 gamated zinc is best used), and illustrate the effect of impurity 

 by adding a drop or two of a lead or copper salt. 



3. Prepare hydrogen by dissolving zinc or aluminium in 

 sodium hydroxide. 



4. Point out that whereas sodium displaces hydrogen from 

 water at ordinary temperature, and that iron does so at a red 

 heat, copper is without any action at any temperature. 



