A CONVENIENT WATER STILL J. GILBERT HOOLEY
AND
NORMAN W. F. PHILLIPS
The University of British Columbia, Vancouver, Canada
D
URING a precise investigation being carried on a t from cylindrical blocks of convenient size. These were this laboratory, large quantities of distilled cast from tin of C.P. grade. water of conductivity grade were required. In the stopper (B) for the still one small hole was Experimentation led to the construction of an efficient electrically heated still with a maximum capacity of about 2 liters per hour. The general arrangement is shown in Figure 1. For the still ( A ) a 12-liter Pyrex balloon flask was used, into the neck of which was fitted a tin plug (B). This was bored to receive a block tin condenser surrounded by a brass water-jacket (C). A similar tin plug (D) was bored to receive the other end of the condenser. This plug was likewise fitted into the neck of a 12-liter Pyrex balloon flask (E)which acted as the receiver.
FIGURE
The heating unit (F) was a 1600-watt nichrome element which rested in a grooved form in a large (10-in.) evaporatmg dish. The latter was supported on a bed of rock wool in a metal container of suitable dimensions. The element consisted of four coils, each made by windmg 30 ft. of 22-gage nichrome wire on a 3/16-in. rod. To construct the form equal volumes of kaolin and purified shredded asbestos were mixed with water to form a paste of the consistency of plasticene. The dish was coated with the mixture to a depth of % in. Grooves were then molded in the layer arranged as shown in Figure 2. The form was then dried sufficiently slowly to avoid distortion. The four coils were placed in the grooves and the electrical circuit was completed as shown. It might be noted that any fraction of the full 1600-watt element can be utilized; the rate of distillation is thus readily controlled. The tin stoppers (B and D) were machined (Figure 3)
WIRING
DIAGRAM OF
HEATING ELEMENT
drilled as shown. This was used for filling the still and was normally closed by a plug made from C.P. stick tin. The filling device consisted of a 6-liter Pyrex Florence flask (G) with a two-hole stopper. Washed air was blown through one hole and the water was 6-foot
n
thereby forced out of a long tube (H)into the still itself. The smaller flask could be easily disengaged and filled from the ordmary distilled water source. The tin stopper (D) for the receiver differed slightly from the first stopper in that it had two small holes.
To one hole was connected a soda-lime tube (I)to remove traces of acid fumes. Through the other hole was fitted a Pyrex tube (J)reaching to the bottom of the receiver. The other end of this tube passed through a cork fitted to a 2-liter pyrex storage flask ( K ) . Another tube inserted through the cork was connected to a vacuum pump. The device was of such a shape that it permitted the raising of the cork, thus allowing ease of insertion and removal from the storage flask. Both tin stoppers were held in place by clamps. To make the condenser, a G-ft. length of 7/s-in. block tin tubing was bent as shown in Figure 4. I t was then sawed in two atthe point indicated, thus givingtwo pipes
of the required shape. A brass water-jacket 20 in. long was soldered onto the condenser. With the still filled with 10 liters of water, and the heating unit fully on, boiling commenced in less than 45 minutes. Unless otherwise adjusted the distillate then came over a t a rate slightly greater than 2 liters an hour. At this rate ebullition proceeded quite evenly, without the slightest trace of spray being carried over, as was shown by tests with dyes. The only attention required besides filling the still and discarding the first portion of the distillate was the occasional cleaning of the still, which was easily accomplished by siphon.
