420 PRACTICAL ORGANIC CHEMISTRY end of the tube as it cools. The tube whenever possible should be left over-night before being heated in the furnace: failing this, at least 3 hours should elapse between sealing and heating in the furnace. Now roll up the Carius tube (while still in a vertical position) in a strip of ordinary thick drying-paper, and then place it in the heavy iron protector tube: if the Carius tube is too short and tends to disappear within the iron tube, a short section of old glass tubing should first be placed in the iron tube so that the capillary of the Carius tube just projects. The function of the paper is to protect the Carius tubing from being scratched, and also (more important) to prevent the local overheat-ing which would otherwise occur at places where the Carius tube is in direct contact with the iron tube. The sealed tube, throughout its manipulation, should be left as nearly vertical as possible, so that the contents do not leave the rounded end.
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