If there is no lead [Footnote:  The wine sold by retail dealers in Paris is rarely free from lead, though some of it does not contain litharge, for the counters are covered with lead and when the wine is poured into the measures and some of it spilt upon the counter and the measures left standing on the counter, some of the lead is always dissolved.  It is strange that so obvious and dangerous an abuse should be tolerated by the police.  But indeed well-to-do people, who rarely drink these wines, are not likely to be poisoned by them.] nor other metal in the wine the alkali will slowly [Footnote:  The vegetable acid is very gentle in its action.  If it were a mineral acid and less diluted, the combination would not take place without effervescence.] combine with the acid, all will remain clear and there will be no precipitate.

Then I poured my alkaline solution first into one glass and then into the other.  The wine from our own house remained clear and unclouded, the other at once became turbid, and an hour later the lead might be plainly seen, precipitated at the bottom of the glass.

“This,” said I, “is a pure natural wine and fit to drink; the other is adulterated and poisonous.  You wanted to know the use of knowing how to make ink.  If you can make ink you can find out what wines are adulterated.”

I was very well pleased with my illustration, but I found it made little impression on my pupil.  When I had time to think about it I saw I had been a fool, for not only was it impossible for a child of twelve to follow my explanations, but the usefulness of the experiment did not appeal to him; he had tasted both glasses of wine and found them both good, so he attached no meaning to the word “adulterated” which I thought I had explained so nicely.  Indeed, the other words, “unwholesome” and “poison,” had no meaning whatever for him; he was in the same condition as the boy who told the story of Philip and his doctor.  It is the condition of all children.

The relation of causes and effects whose connection is unknown to us, good and ill of which we have no idea, the needs we have never felt, have no existence for us.  It is impossible to interest ourselves in them sufficiently to make us do anything connected with them.  At fifteen we become aware of the happiness of a good man, as at thirty we become aware of the glory of Paradise.  If we had no clear idea of either we should make no effort for their attainment; and even if we had a clear idea of them, we should make little or no effort unless we desired them and unless we felt we were made for them.  It is easy to convince a child that what you wish to teach him is useful, but it is useless to convince if you cannot also persuade.  Pure reason may lead us to approve or censure, but it is feeling which leads to action, and how shall we care about that which does not concern us?