“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.

“Forgive me,” said Charlotte, “as I forgive the natural philosopher.  I cannot see any choice in this; I see a natural necessity rather, and scarcely that.  After all, it is perhaps merely a case of opportunity.  Opportunity makes relations as it makes thieves; and as long as the talk is only of natural substances, the choice to me appears to be altogether in the hands of the chemist who brings the creatures together.  Once, however, let them be brought together, and then God have mercy on them.  In the present case, I cannot help being sorry for the poor acid gas, which is driven out up and down infinity again.”

“The acid’s business,” answered the Captain, “is now to get connected with water, and so serve as a mineral fountain for the refreshing of sound or disordered mankind.”

“That is very well for the gypsum to say,” said Charlotte.  “The gypsum is all right, is a body, is provided for.  The other poor, desolate creature may have trouble enough to go through before it can find a second home for itself.”

“I am much mistaken,” said Edward, smiling, “if there be not some little arriere pensee behind this.  Confess your wickedness!  You mean me by your lime; the lime is laid hold of by the Captain, in the form of sulphuric acid, torn away from your agreeable society, and metamorphosed into a refractory gypsum.”