Note 12 — PART II. (continued 3)

These white vapours do not appear when the vessels are perfectly close. Mr. Hellot, to whom we owe the remark, having performed this operation in a crystal retort procured from London, the neck of which had been rubbed with emery in the mouth of its receiver, so that these two vessels fitted each other exactly, saw the ætherial liquor distil pretty fast, but without white vapours. He then loosened the receiver, by turning it a little upon the neck of the retort, so that the external air might get in; whereupon the white vapours appeared immediately. When the receiver was close fitted on again, the vapours disappeared. He repeated the same thing five times from half hour to half hour, and these vapours as often appeared and disappeared.