Adapters for Collection of Distillation Fractions under Vacuum JOHN W . PlTTERSON AND ROBERT W. VANDOL-AH,The Ohio State University, Columbus, Ohio
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ECEIVERS are usually changed during low-pressure
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distillation: (1) by the use of a series of stopcocks which permit the complete removal and replacement of the receiver, or (2) by the use of glass adapters, sometimes known as “cows”, which lead the distillate into receivers already connected to the vacuum system. Since either method involves special equipment, which may not be available, two adapters are described in this paper which can be made a t low cost and without a mastery of the technique of glass blowing. The design of the first model (Figure 1) is adapted from Bruhl ( I ) , uses only commonly available materials, and is very useful in working with small quantities of liquids. Although the dimensions are not critical, those of the apparatus in use in this laboratory are given as a n example.
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FIGURE 2
are held in position by rubber bands. By means of the wire handle it is possible to rotate the metal frame and place the desired receiver under the drip point of the condenser.
FIGURE 1
B y modifying the first design slightly it is possible to obtain a second model (Figure 2) more suitable for the collection of larger fractions.
The outer jacket is made from a 12-cm. length of 48-mm. tubing with No. 10 rubber stoppers fitted in the ends. Passing through the lower, and extending to a glass bearing in the upper stopper is a 3-mm. wire, which is bent a t its free end to form a handle. To this wire are soldered, a t right angles to each other, four metal vanes with the lower ends bent horizontally to form a platform. The upper stopper is fitted with a condenser (optional) and a bent tube leading to a vacuum pump. In operation, four 80 X 15 mm. vials are placed in the corners produced by the vanes and
The outer jacket is the same, but the stoppers are fitted with different attachments. In this case it is necessary to center the drip point of the condenser so that the falling distillate will be caught by the rotating adapter, which consists of a short length of 10-mm. tubin , flanged at one end and ground t o a drip point a t the other. kince the proper functionin of this rotating adapter requires that the upper end be practicafly free from lateral 511
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motion, it is supported by a 3-mm. wire handle extending through the lower stopper and bent so that the wire and upper portion of the glass tube have the same axis. The tube is held to the wire by a piece of thin metal sheeting soldered to the wire and bent around the glass at two points. In the lower stopper are also placed four slightly bent &mm. glass tubes, which are flanged at the upper end and placed so that the centers are equidistant from the wire. When in operation, four receivers are attached to these delivery tubes by means of rubber stoppers, and then as a drop of distillate leaves the condenser it can be directed by means of the rotating adapter to any one of the delivery tubes and thus to the receiver. Adapters of the type described are free from the usual susceptibility to damage caused by thermal and mechanical strains. The rubber stoppers, do not lower the efficiency of operation, since pressures as low as 1mm. have been obtained, nor do they affect the purity of product, since at no time is the
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distillate in contact with any material other than glass. Moreover, the individual adapters offer certain advantages. The first model is designed for small fractions, but the capacity can easily be varied by changing the length of the whole system. The use of fragile, preweighed vials as direct receivers is a n important convenience in working with small quantities where losses due to transfer are appreciable. The second suggested design is of such a nature that it is not necessary to change the position of the receivers when changing fractions. Thus, receivers can be held firmly and may even be large and heavy, since changing fractions merely requires twisting the wire handle.
Literature Cited (1) Bruhl, Ber., 21, 3339 (1888).
Ferrocyanide Method for Separation of Hafnium from Zirconium W,4LTER C. SCHUMB AND FRANK K. PITThIAN Massachusetts Institute of Technology, Cambridge, Mass.
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OST of the methods for the separation of hafnium from zirconium depend upon the repeated fractional crystallization or precipitation of such compounds as the oxychloride, phosphate, oxalate, fluohafnate, etc., and the number of fractionations required in general is large. I n 1932 Prandtl ( 2 ) described a procedure by n-hich the separation of these elements may be effected in comparatively few operations by precipitation of the ferrocyanides, yielding a product containing 90 per cent hafnium oxide and 10 per cent zirconium oxide starting with a material containing about 1 per cent hafnium oxide. Of all the methods reported thus far, this would appear to be the fastest and most efficient. I n certain details the procedure described by Prandtl is somewhat indefinite, such as the actual concentration of sulfuric acid which should be present in the solution prior to precipitation with sodium ferrocyanide and the proper quantity of sodium ferrocyanide to be used in the precipitations. Since the authors’ preliminary experiments with the method gave results somewhat a t variance with those reported by Prandtl, it was decided to examine more closely the conditions under which separation by this procedure may be accomplished. The method described by Prandtl depends upon the fractional precipitation of the ferrocyanides of zirconium and hafnium from a solution containing oxalate and sulfate ion, t h e purpose of which is to form complex ions of different stability. The hafnium is enriched in the precipitate. PROCEDURE. Zirconium (and hafnium) hydroxide is precipitated from a solution of the oxychloride by means of ammonium hydroxide. The precipitate is filtered and treated with just enough dilute sulfuric acid to cause it to dissolve. This takes several hours, because the reaction must be carried out at room temperature. An amount of ammonium sulfate at least equal to the weight of oxide in the solution is added to the clear solution, which is warmed for several hours. If no precipitate forms, a solution of oxalic acid saturated in the cold is added in the ratio of 200 cc. of oxalic acid for each 100 grams of oxide prestnt. To this solution, still warm, is now added with stirring a solution of sodium ferrocyanide containing a weight of SaaFe(CS)s.10H20equal t o that of the oxide in solution.
(Some ambiguity exists in the original description at this point, which is as follows: “ich . . . . eine Losung von soviel , . . Xatriumferrocyanid zuset,zte, als dem Gewicht des in Losung vorhandenen Zirkonium-Hafniumoxydes entsprach.” That this implies an amount of ferrocyanide equal to the weight of the mixed oxides is assumed, since if it were to mean equivalent to, the precipitation of both zirconium and hafnium would be complete and no separation effected. Furthermore, in referring to the addition of ammonium sulfate, in the same paragraph, an almost identical construction is used which leaves no doubt as to its meaning: “Zu dieser Losung setzt man mindestens so vie1 Ammoniumsulfat hinzu, als das Gewicht des in der Losung vorhandenen Zirkonium-Hafniumoxydes betrfigt. ”) The mixture is allowed to stand with stirring at room temperature for several hours. The resulting yellow precipitate is then filtered and converted to the hydroxide by digestion with excess concentrated sodium hydroxide. (The precipitate will be greenish-yellow if iron is present, but this does not affect the efficiency of the separation.) The process may then be repeated with this mixture of zirconium and hafnium hydroxides. I n illustrative data quoted by Prandtl, the addition of 500 grams of sodium ferrocyanide to 1 kg. of zirconium oxide was said to give 40 grams of enriched zirconium oxide. The concentration of the starting material was given as about 1.3 per cent hafnium oxide and that of the product as 20 per cent hafnium oxide. There appears to be a discrepancy between the body of the report, which calls for a 1 to 1 ratio of ferrocyanide to oxide, and these data which call for a 1 to 2 ratio. I n repeating the experiment just referred to, using the 1 to 2 ratio, the authors obtained the following results (calculated to the same basis as Prandtl’s) : The addition of 500 grams of sodium ferrocyanide to 1 kg. of zirconium oxide (12 per cent hafnium oxide) yielded 200 grams of zirconium oxide (18 per cent hafnium oxide). These results differed from those of Prandtl in the amount of material precipitated, the increase in the ratio of hafnium to zirconium, and the efficiency of the enrichment of the hafnium oxide. It was felt that the cause of these discrepancies could be found in the ambiguities in the original paper above referred to. This led to the undertaking of a detailed study of the factors affecting the separation.
