Caustic soda and spirits of salt are now shown to the children. Here the polarities of acid and alkali are much more obvious, they are tabulated graphically:—
ACID ALKALI
Sharp Dull
Red colouring Blue colouring
Awakens Dulls the tongue’s sense of Taste
Gaseous Solid
The whole thing is now shewn in its relationship to man. Every time the arm is moved, acid is formed in the muscles. When we walk or run or indeed do any sort of work acid is formed in the human body. But we may also sit still in our room and think. No acid now appears, but instead basic or alkaline substances are formed in the brain. When we move, our muscles turn sour, when thoughts move in our heads as we sit resting, our heads become alkaline within. A base is formed. Thus acid and alkali play their part in us too. (I owe this example to Rudolf Steiner who made use of it when instructing a class on the occasion of a visit to the Waldorf School.)
The same contrariety can be shown in the plant world. In the roots there is a preponderance of base, while the leaves, fruits and sprouting parts generally are acid. The sour taste of the wood sorrel will be familiar to all, its roots, however, taste salty and alkaline. There is no need at this stage to speak of the exceptions to this law, because these exceptions will make an important lesson later on.
The matter in this section is summarised in the following dictation:—
“The two opposites may also be extracted from salt. They are Hydrochloric acid gas, and sodium base. The gas has a strong pungent smell and a sharp sour taste. It colours litmus paper red. Its property is to awaken, for it is an active substance. But the caustic soda is insipid and deadens the sense of taste. It gives a blue reaction with litmus paper. Like caustic soda, most bases are solids. Their nature is essentially heavy. Thus the roots of plants tend to be basic while their leaves are acid and have a sour taste like wood sorrel. Acid has affinity to the air, base to the earth. With man the tendency is reversed, the activity of the legs produces acid, while quiet thought awakens an alkaline, basic condition in the head, where, incidentally there is also much chalk. Acid and alkali thus appear as two great opposites whose interaction may be observed throughout all nature.”
During a subsequent lesson, the children should be encouraged to represent this antithesis in a picture. They are by now familiar with the contrasting colours that acid and alkali produce with litmus, and they are now asked to depict the battle between the two. To make the reaction more vivid for them, a quantity of concentrated hydrochloric acid should be mixed with strong caustic soda solution. They will observe the extreme violence of the reaction, so much more violent than when lime was slaked. The liquid seethes and splutters and fumes. When the children express this in colour, letting the red mingle with the blue, quite remarkable pictures result. The characteristics of all the different temperaments reveal themselves. This provides an opportunity of experiencing this fundamental chemical antithesis with the artistic side of the nature. An element both scientific and artistic has been awakened in the child. (It would be absurd from the educational point of view, to introduce the concepts of acid and alkali with talk of Hydrogen and Hydrates (Hydroyl), a tendency that is all too common today, even in school books.) The interaction between acid and alkali that proceeds throughout the universe and in man too, has now been surveyed.
The child has been introduced into quite a new department of chemistry. First it learnt about combustion, now it also knows about salt formation. Before proceeding any further with the lessons it is advisable to bring out again very forcibly, the contrast between these two processes.