It is not easy or even possible to discuss the chemical properties of substances without the use of chemical terms. Substances are classified for chemical purposes in groups, every member of which exhibits the same chemical property, and we shall require to distinguish between the group called acids and the group called alkalies. It will be sufficient for our purpose just now to know that acids have a sour taste and that alkalies counteract acids. From this definition lemon-juice will easily be recognised as an acid. If we add soda to lemon-juice there will be a brisk effervescence and the lemon-juice will no longer be sour, hence soda is an alkali. Alkalies have another well-known chemical property--they dissolve grease and oil and enable them to mix with water. If we have some hot water in a tumbler and pour oil into it the oil will float on the water, and if we stir the two together the oil will break into globules but will still float on the water; we cannot mix them together. If we dissolve some soda in hot water and pour in oil we shall find on stirring that the mixture becomes milky or soapy in appearance and the oil and water are no longer discernible as different fluids. Moreover, on standing the oil will not again separate from the water; it has been emulsified. Oils themselves have the chemical power of dissolving resins. Resins are hard, bright vegetable gums which will come under our notice when we consider the composition of varnishes. All hard soaps are made from soda, grease, and resin; the cheaper soaps contain free soda, the dearer ones contain an excess of fat. Yellow scrubbing soap contains about eight per cent. of free soda. Both soap and soda can be dissolved in water, and are so dissolved for cleaning purposes. Knowing the constituents of our cleansing agents, we can consider their action on paint and varnish. Paint contains white-lead, linseed-oil, and colouring matter. It is not very hard when dry and can be easily scratched with the nail. Varnish is made from linseed-oil, resin, and turpentine. When dry it should be very hard and bright. The whole of the painted woodwork of the house is subjected to spring-cleaning whatever its appearance with regard to dirt may be. The operator throws into a pailful of hot water a "handful" of soda, soaks a scrubbing-brush in the mixture, rubs it well with soap, and uses it to brush the somewhat soft paint or harder varnish. The soda and soap, aided by the heat, soften the paint and the brush removes a quantity equal to about a coat of paint. The effect is certainly pleasing for the time being, but there will be no difficulty in understanding that the process can only be repeated until the paint and varnish grow shabby or disappear.