166 REPORTS ON THE STATE OF SCIENCE.—1917. 
E. Chemistry. 
Nore.—§§ 1-4 should be taken during Autumn Term. 
1. Washing soda a crystalline substance which degenerates (especially in 
warm weather) into a shapeless powder. Distillation shows changes to be due 
to loss of ‘water of crystallisation.’ Water derivable from other crystals (but 
not all) and from vegetable and animal substances (e.g. a potato) where its 
presence is not apparent. First notions of chemical combination between 
substances. 
Crystallisation from solution in water. Manufacture of common salt, cane 
and beet sugar; plaster of Paris; ‘ sympathetic inks.’ Variations in solubility. 
Crystalloids and colloids. Other solvents (e.g. petrol, solvent naphtha in water- 
proofing, turpentine, &c.) and their uses. 
Soluble and insoluble substances in soil. Residue from evaporation of tap- 
water; formation of sea-water. 
2. Use of soda in cookery leads to discovery that it turns the juice of 
pickling cabbage green. (The juice is extracted by pounding in a mortar.) 
Vinegar (preferably ‘ white’ vinegar) turns the juice red. Soda and vinegar 
can ‘ overcome’ one another’s effects. Caustic soda, mild and caustic potash, 
ammonia and lime, being found to turn the juice green, are classed with washing 
soda as alkalis; acids are found to turn it red. Other vegetable extracts found 
to show colour changes with acids and alkalis, e.g. litmus. Other ‘indicators’ : 
phepolphthalein, methyl orange. 
Neutralisation; careful study by means of burette, different boys working 
with different acids and alkalis. Evaporation of neutral solutions reveals 
presence of common salt when mild or caustic soda is neutralised by hydrochloric 
acid, and other ‘ salts’ in the other cases. Salts named from acid and alkali 
(e.g. sulphate of ammonia). Manufacture of sulphate of ammonia for manure, 
and of sal-ammoniac. 
3. How does caustic differ from washing soda? On addition of acid the 
latter yields a heavy gas which extinguishes flames, turns lime-water cloudy 
and ultimately clears it again. The cloudy matter, when collected, returns the 
gas if acid is added. Chalk is known to yield the same gas when ‘ burnt’ 
to make lime. Finally, caustic soda is made by boiling washing soda with 
lime, the latter becoming converted into chalk. (Similar statements apply to 
mild and caustic potash.) Thus, washing soda, mild potash, and chalk are to 
be classed together, and also caustic soda, caustic potash and lime. But there 
are two ‘limes ’—quicklime and slaked lime. Dry ‘ heavy gas’ liberates water 
from caustic soda, caustic potash and slaked lime, but not from quicklime; 
hence the analogy is with slaked lime. 
4. The ‘heavy gas’ is produced in breathing, and also in the burning of 
coal-gas, candles, &c. Burning of these substances in a jar demonstrates its 
production together with water, and shows, further, that one-fifth of the air 
is consumed. The burning of metals (e.g. magnesium), and of phosphorus, 
sulphur, &c., the rusting of iron, the ‘drying’ of boiled oil, &c., also remove 
the ‘active’ one-fifth of the air and leave four-fifths ‘inactive.’ Consideration 
of the mode of manufacture of red lead suggests that if heated it may restore 
the absorbed active constituent. Oxygen and nitrogen; argon. Manufacture of 
oxygen from liquid air. Properties and uses of oxygen. Oxides. 
The ‘heavy gas’ is produced without water when pure carbon is burnt in 
oxygen. It is, therefore, an oxide of carbon. Confirmation by burning mag- 
nesium in gas. Oxygen passed over red-hot carbon (as in a domestic fire and 
in the smelting furnace) produces a gas which burns to form the heavy gas. 
The latter must, therefore, contain more oxygen (compare litharge and red 
lead) ; hence the names carbon monoxide and carbon dioxide. 
5. Oxides and oxidation in nature and industry. Oxides of iron, copper, 
magnesium, aluminium, &c.; ochres and other painter’s colours; ‘ drying’ of 
oils; linoleum. : 
6. Is water also an oxide? Affirmative answer obtained by passing steam 
over hot magnesium. Discovery of hydrogen. Production in bulk by passing 
steam over hot iron; properties. Known to be produced also when the plumber 
‘kills spirits of salt’ with zinc. Composition of water confirmed by burning a 
