Jay E. Taylor University
of
An Apparatus for the Continous
Nebraska
Lincoln 8
Production of Triple Distilled Water
In this laboratory there has been a constant need for water of very high purity. In designing equipment to answer this need the following factors were taken into account: (1) the highest purity product should be obtained; (2) a minimum of attention should be devoted to the apparatus while i t is running; (3) time spent on upkeep or repairs should be negligible. The combination still described below has very satisfactorily fulfilled these requirements. There is an additional less important but quite amusing feature associated with this apparatus; this is the high "comment quotient" which, because of bubbling permanganate and the various tubes and siphons, often exceeds that stimulated by more complex apparatus. The cycle starts with the five gallon reservoir A in which tap distilled water is stored. The maximum length of running time of the still is determined by the capacity of this reservoir. The water from A siphons continuously into container B and the level is kept constant with the leveling device as shown. From B the water passes through tube C and into the one liter distillation pot D which contains dilute basic permanganate. The glass check valve a t C prevents hacksurge of the water from D into B. Using a Bunsen burner the water in D is distilled through the Vigrenx column and condenser a t E and into F. The Bunsen burner flame is protected from currents of air as shown and the rim around flask D prevents overheating of the glass area above the boiling water. The purpose of the tube a t F is to provide a constant supply of water for the distillation pot a t J . Since i t is quite diicult to set the rate of distillation of water from D exactly equal to the rate of distillation from J , an overflow reservoir is provided a t G so that still D may be run faster than J . The air space seen in F prevents possible contamination of the ovediow distillate because of back diffusion of water from pot J . The check valve a t H prevents backsurge of the boiling water. Pot J , containing very dilute sulfuric acid is heated similarly to D. The final distillate passes through the Vigreux column and condenser a t K and is collected in the reservoir L which is equipped with a greaseless stopcock. One serious problem associated with any distillation is humping. This is prevented by an inverted 2 mm capillary tube in J. It is necessary to shake this capillary so that it will a t least he partially filled with air each time before the still is started. Due to the greater tendency of basic solutions to hump, a more elaborate setup is used in D. The cooling water passes first through the condensers E and K and then into the air reservoir M. Pressure equal to a head of water of the height QM develops and the overflow water passes out through the T-tube a t Q. The air trapped very slowly
escapes through the fine capillary a t R and bubbles into the bottom of pot D thereby providing a continuous flow of bubbles to prevent bumping. The capillary a t R should he sufficiently small so that a t least twenty hours are required to displace the air in M.
The organic matter which inevitably accompanies distilled water produced from central steam supplies is oxidized by the basic permanganate solution in D. This solution is made by adding 3-5 ml of saturated KMnOa and the same amount of 1 M sodium or potassium hydroxide each time the pot is cleaned out. For best results, the pot D should be cleaned after each emptying of water reservoir A simply by siphoning. The contents of pot J include 2-3 ml of concentrated sulfuric acid added to neutralize any amines or other basic wbstances which may possibly distill from D. This solution need not be changed for long periods. The water produced is of high quality. The conductivity of the water will depend on the care which has been taken in preventing contact of the water with carbon dioxide of the atmosphere. If snperconductivity water is desired, it would be well to replace the Bunsen burners by electrical resistance heaters and to protect all openings to the atmosphere by tubes containing Ascarite, soda lime, or other carbon dioxide absorbent.
Organic and mineral impurities only have been of prime concern in thislaboratory so this precaution hasnot been observed. This apparatus accomplishes its purpose in a highly efficient and trouble-free manner. To turn it on in the morning the stopcock a t P is closed, the condenser water is turned on, and the burners are ignited. The only care required during the day is to empty the reservoir L of triple distilled water when it becomes filled. At the close of the day the burners are turned off,stopcock P is closed, and the condenser water is turned off. The antibumping capillary should be lifted up above the surface of the water in flask J for a short time after
the distillation stops, and then it will require no attention the next morning. To refill the five gallon reservoir a t A the distillation is allowed to continue until the siphon in tube AB breaks. Tap distilled water is then run into A until the bottle is filled and the water is forced back into siphon AB. The stills D and J need not be stopped for this operation. It may be noted from the diagram that the burners are directed against bare glass. The advantage is maximum heat exchange. If this setup is used, it is important that the flasks do not go dry after depletion of the reservoir A, or the stills may crack.
Volume 37, Number 4, April 1960
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