The offset type of still-head shown in the preceding diagrams works very well, but you may prefer to use the linear design shown here:
It has several advantages over the previous model. They are:
1) It is cheaper to make since it involves no T's or elbows;
2) No corks are involved for the thermometer;
3) It is more streamlined and elegant in appearance.
Construction. The diagram illustrates the design concept but a few construction details are necessary.
a) The collection "spoon" is cut from 3/8 inch copper tubing. A metal-cutting blade on a table-saw is useful for this purpose. Use a 3 inch length of tubing and remove one-half of the diameter for a distance of 1 inch from one end. Cut "nicks" at the root of the trough so that the trough can be slightly flattened to give a shallow spoon 1/2 inch wide.
b) Drill a 25/64 inch hole in the column 13 inches from the top and tilt the drill bit to elongate the hole to an oval — 1/2 inch along its major axis. The spoon will now enter the hole if tilted sideways. Turn it 90o and spring-load to hold it in position at a 45o angle while soldering in place. Attach a 1/4 inch needle valve using a 3/8 x 1/4 inch compression coupling.
c) For the thermometer, drill a 25/64 inch hole 141/2 inches from the top of the column on the opposite side to the collection spoon. Elongate the hole into an oval by tilting the drill bit in exactly the same manner as in b) above.
Take a 3 inch length of 3/8 inch tubing and remove one half of the diameter for a distance of 1 inch from one end, just as in a) above. Insert it in the hole so that the open side of the trough is facing down and the closed side facing up. Solder it in place at an angle of 45o The purpose of this design is to shield the thermometer bulb from dripping condensate while leaving it exposed to rising vapours.
d) Using a 3/8 x 1/4 inch compression coupling, drill through with a 17/64 inch bit (or slightly larger) from the 3/8 inch end to remove the internal shoulder. Be careful not to go all the way through as this would remove a little of the seat for the 1/4 inch ferule at the other end. A mercury/glass thermometer should now slip through nicely. For sealing, a brass ferule is not possible, but a very effective seal is obtained by wrapping a few turns of teflon plumber's tape around the stem and compressing with the nut on the coupling.
Note 1. Some thermometers may have stems which are slightly too large in diameter to go through a 17/64 inch hole. Be careful, therefore, to choose a thermometer which will go through. Or, drill a larger hole.
Note 2. A glass thermometer in such a rigid set-up is very vulnerable to breakage. It is prudent, therefore, to remove it while working around the still.
Note 3. By using a 3/8 inch needle valve one can eliminate one of the 3/8 x 1/4 inch compression couplings.
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