"Then again," replied Edward, "as these are united under common laws and customs, so there are intermediate members in our chemical world which will combine elements that are mutually repulsive."
"Oil, for instance," said the Captain, "we make combine with water with the help of alkalis——"
"Do not go on too fast with your lesson," said Charlotte. "Let me see that I keep step with you. Are we not here arrived among the affinities?"
"Exactly," replied the Captain; "we are on the point of apprehending them in all their power and distinctness; such natures as, when they come in contact, at once lay hold of each other, each mutually affecting the other, we speak of as having an affinity one for the other. With the alkalis and acids, for instance, the affinities are strikingly marked. They are of opposite natures; very likely their being of opposite natures is the secret of their inter-relational effect—each reaches out eagerly for its companion, they lay hold of each other, modify each other's character, and form in connection an entirely new substance. There is lime, you remember, which shows the strongest inclination for all sorts of acids—a distinct desire of combining with them. As soon as our chemical chest arrives, we can show you a number of entertaining experiments which will give you a clearer idea than words, and names, and technical expressions."
"It appears to me," said Charlotte, "that, if you choose to call these strange creatures of yours related, the relationship is not so much a relationship of blood as of soul or of spirit. It is the way in which we see all really deep friendship arise among men, opposite peculiarities of disposition being what best makes internal union possible. But I will wait to see what you can really show me of these mysterious proceedings; and for the present," she added, turning to Edward, "I will promise not to disturb you any more in your reading. You have taught me enough of what it is about to enable me to attend to it."
"No, no," replied Edward, "now that you have once stirred the thing, you shall not get off so easily. It is just the most complicated cases which are the most interesting. In these you come first to see the degrees of the affinities, to watch them as their power of attraction is weaker or stronger, nearer or more remote. Affinities begin really to interest only when they bring about separations."
"What!" cried Charlotte, "is that miserable word, which unhappily we hear so often now-a-days in the world; is that to be found in nature's lessons too?"
"Most certainly," answered Edward; "the title with which chemists were supposed to be most honorably distinguished was, artists of separation."
"It is not so any more," replied Charlotte; "and it is well that it is not. It is a higher art, and it is a higher merit, to unite. An artist of union is what we should welcome in every province of the universe. However, as we are on the subject again, give me an instance or two of what you mean."
"We had better keep," said the Captain, "to the same instances of which we have already been speaking. Thus, what we call limestone is a more or less pure calcareous earth in combination with a delicate acid, which is familiar to us in the form of a gas. Now, if we place a piece of this stone in diluted sulphuric acid, this will take possession of the lime, and appear with it in the form of gypsum, the gaseous acid at the same time going off in vapor. Here is a case of separation; a combination arises, and we believe ourselves now justified in applying to it the words 'Elective Affinity;' it really looks as if one relation had been deliberately chosen in preference to another.