This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A simple and very effective device to replace the cumbersome cooling or condensation coil of a still for the amateur's laboratory can be easily made as follows:
Procure an ordinary straight glass tube of fairly large diameter and heat it in the flame of an alcohol lamp with the use of a blowpipe or in a Bunsen burner with a very reduced flame so that only a small spot of the tube is brought to a red heat at one time. Then, with a previously pointed and charred stick of wood - a penholder, for instance - produce a small recess in the wall by pushing the charred end gently into the glowing part of the tube. This procedure is repeated until the whole tube is thus provided with small recesses. The indentations should be made in spiral lines around the tube, thus increasing the surface that is in contact with the cooling water. The operation of making the recesses is shown in Fig. 1. The walls of the recesses should have a regular and uniform slant.
The tube thus produced can either be used as a rectifier (Fig. 2) above a vessel, for fractional distillation, because it will allow the most volatile parts to pass out first, or as a condenser (Fig. 3), the arrangement of which needs no explanation. The amateur will find it much easier to make this tube than to coil a very long one.