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!
THE CHEMISTRY OF THE BODY
It is to the science of chemistry that we owe our knowledge of the composition of the various foodstuffs from which dietaries are selected, as well as of the several parts of the human body which relies for its sustenance on those dietaries. But the adjustment of dietaries to the work they have to do is a more complex problem than those we have hitherto considered. We learn from the science of physiology that the human body is a laboratory in which certain juices are secreted for the digestion of foods, and that in this laboratory 117 foods must be reduced to the consistency necessary for their passage through animal membranes; for it is by passage through membranes that the nutritive parts of food find their way into the general circulation of the blood which carries them to all parts of the system. Very few foodstuffs are available for use in their natural state, and the majority of them are prepared for consumption in the first place by more or less elaborate processes included in the art of cookery. When thus prepared they should be in a fit state to undergo in the body the physical changes comprised in mastication, and the chemical changes associated with the process of digestion.
It might be surmised by the thoughtful parent that as the child’s body lacks some of the external features of the adult body, such as hair and teeth, so there might, and probably would, be corresponding lapses in the internal economy, and that therefore the food prepared for the adult would be, even in the smallest quantity, unsuited to the child. Physiologists tell us that this is so, and in particular that the secretions which in adult life are called saliva and pancreatic juice and which have the function of preparing starch for digestion, are at this time scanty in amount and deficient in chemical action. But these secretions are essential for the digestion of starchy foods, and chemists tell us that starch abounds in the vegetable kingdom from which most of the food of children is derived. It is therefore a matter of some importance that every person in charge of 118 an infant should have that amount of knowledge of chemical reactions which is requisite to enable them to detect whether a food does or does not contain starch. A child fed entirely on starchy foods suffers from malnutrition of so serious a character that death may, and often does, ensue. Even if other suitable food, such as modified milk, be given, the internal economy of the child will be seriously disturbed.
The names by which patent foods are advertised are very often misleading to unscientific persons, and invalids have suffered much from the mistaken idea that jellies and meat extracts are foods. Meat extracts have their use, but any invalid fed on extract of beef only would die sooner than one left with no food at all. The reason for this can be learned from the knowledge of the constituents of beef extracts and the part they play in the human organism.
CONCLUSION
If we have seemed to lay stress on the value of a knowledge of the sciences of physics and chemistry to the exclusion of the mention of others, our justification of the fact is that space is limited, and that we believe that physics and chemistry underlie all the other sciences and are of paramount importance to students of all other subjects. In the sciences of biology, physiology, botany, geology, &c., little advance can be made without a knowledge of the fundamental 119 laws of nature. The physical laws control movement, and the chemical laws control growth, whether of animate or inanimate nature. Physical and chemical phenomena are concerned in the upheaval of rocks and mountains which govern the contour of the continents of the world. These contours influence climates and peoples; as the contours change the people change. The dwellers in the mountain regions differ in character from the dwellers in valleys and plains; the inhabitants of cold districts differ from the inhabitants of warm districts; but it is people who make history, and historians cannot afford to pass by natural environments and natural laws.
If a foundation of the fundamental sciences be laid at school the student can subsequently build upon it the special science that is suited to his career. It matters little what the calling in life of any person may be; if he aim at success in that calling he must acquaint himself with the laws by which he has his being, and by which he must perforce be guided in all his actions as well as in his intercourse with his fellow-men.