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68 well stoppered so far as the alcohol is concerned; the air can pass through, but the alcohol cannot. And if I were to take an oil vessel this plan would do equally well, for in former times they used to send us oil from Italy in flasks stoppered only with cotton wool (at the present time the cotton is put in after the oil has arrived here, but formerly it used to be sent so stoppered). Now if it were not for the particles of

Fig. 22.Fig. 23.

liquid cohering together, this alcohol would run out, and if I had time I could have shown you a vessel with the top, bottom and sides altogether formed like a sieve, and yet it would hold water owing to this cohesion.

You have now seen that the solid water can become fluid by the addition of heat, owing to this lessening the attractive force between its