CHEMICAL SCIENCE IN THE HOUSEHOLD
In our endeavour to establish the claims of the science of chemistry to a prominent place in the educational equipment of women, all reference to those most interesting and important chemical phenomena that accompany the exercise of the physiological functions will be omitted; as also those which are most immediately concerned with the preparation of food. Attention will be confined to some of the common occurrences of daily life, the methods of dealing with which are typical of the method adopted in considering more important and abstruse problems.
Perhaps one of the most disappointing experiences of the novice in housekeeping is the rapidity with which everything assumes a shabby aspect. Bright paint grows dull, dull paint wears away, curtains and fabrics fade, and very soon mistress and maids alike feel that the house no longer repays the trouble incurred in the spring-cleaning that it must still undergo. This spring-cleaning, the primary object of which is the preservation of the beauty and substance of the 111 house and its appointments, is in the result the cause of much of their deterioration.
Cleaning consists in removing dirt by means that are partly physical and partly chemical; for instance, the removal of dust by sweeping, shaking, or brushing is a physical operation, and the removal of dirt and grease by dissolving them in soapy water involves their change by a chemical process. If the surfaces or materials to be cleaned include a substance on which the cleansing agent can operate the agent will not confine its work to the removal of the dirt only; in washing coloured fabrics we know how often the colour comes out with the dirt. Knowledge therefore, not only of the composition and properties of cleansing agents, but also of the surfaces and materials to which they are to be applied, is essential, and we should find that it is not always the powder or paste which makes the greatest show of cleanliness in the shortest time, with least expenditure of labour, that is the most to be desired.
The use of alkalies.—The most common cleansing agents are hot water, soap, and soda. Hot water is itself a detergent; that is, it has the power of dissolving dirt. It does not, however, dissolve grease, and all household dirt is more or less greasy, hence we cannot do our cleansing with water only, and we are accustomed to add to it soap or soda.
It is not easy or even possible to discuss the chemical properties of substances without the use 112 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 113 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.
It is not wise for the inexpert housewife to trust to unscientific friends for advice as to the best materials to use when cleaning paint. A foreman painter once gave, as a recipe for this purpose, an instruction to add a tablespoonful of “salts of tartar” to three-quarters of a pailful of water. The result was a very rapid and complete removal 114 of dirt from the paint, but the housewife, being dissatisfied with the rather dull appearance of the white varnish, stroked it with her finger and found that it was covered with a fine white powder. The maid’s assurance that this was all right and only needed to be removed by dusting did not satisfy her, and she began to wonder what chemical action was to be expected from “salts of tartar.” A first search for information revealed that salts of tartar was an old name for “potassium carbonate,” but the housewife knew no chemistry and had never heard of potassium carbonate, so this information was useless to her. She had, however, had some scientific training and was not satisfied to rest in ignorance. A search in a book on elementary chemistry disclosed the further truth that the commercial name for “potassium carbonate” is pearlash! She then remembered that being desirous at one time to remove the paint from some oak carving said to be two hundred years’ old, she had successfully used a solution of pearlash painted on with a brush. The paint when dry from the application had been scraped off in long, tough ribbons. Of course the mixture had been very much stronger than that prescribed by the painter, but the effect had been very much more apparent.
Acids and alkalies are to some extent responsible for the fading of fabrics in the wash when these fabrics owe their colour to vegetable dyes. Acids turn vegetable blues red, alkalies turn vegetable blues green and vegetable yellows brown. 115 It is easy to illustrate this action of acids and alkalies on vegetable colours. A blue liquid can be obtained by boiling a red cabbage in water. If we take two portions of this water and add any acid, say lemon-juice, to one portion we shall obtain a red liquid; if we add any alkali, say soda, to the other portion we shall obtain a green liquid. If we go a step further and add lemon-juice to the green liquid and soda to the red liquid we may approach very nearly to our original blue liquid. These experiments suggest a remedy for the change of colour in fabrics on washing with soda, but the dyes most commonly used are not vegetable dyes, and the fading of the fabrics is due to chemical changes, into which we have no space to enter.
Strong acids and alkalies act as caustics; that is they destroy fabrics. Continued washing in strong soda and water not only tends to destroy, but also spoils the appearance of all kinds of wearing apparel and household linen. White silk and wool at once become yellow on being washed with soap that contains free soda, and linen is affected in the same way though not to the same extent.
The widely advertised pastes and liquids for cleaning metal-work, particularly brass, often contain acids or alkalies that are injurious to metals. If after cleaning there should be a green deposit on brass or copper it will be wise to inquire into the composition of such deposit, and to discontinue the use of that paste or liquid. When brass pans are used for boiling fruit for jams, it is usual to rub them inside with a slice of 116 lemon before putting in the fruit. A careful housewife will consider the reason for this custom. We remember once seeing a copper pan, that had been provided for the preparation of oatmeal porridge, with a band about an inch wide of green crystals on the inside. Inquiry elicited that the cook had thought it a convenient pan in which to prepare the fish (salt haddock) for breakfast. Ignorance of the chemical action of salt and acids on metals may lead to very serious results. The common name for the green deposit on brass and copper is verdigris, and most people know that verdigris is a poisonous compound; the difficulty is that, not knowing its chemical composition, they do not recognise verdigris when they see it. The cook thought that the complaint made had reference only to the misuse of the pan, and said that it was quite easy to clean the green deposit off!