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C.S. & S. 589 (Black Ribbon). , C.S. & S. 589 (Blue Ribbon). THE CHEMICAL NEWS VOL. CXIV., No. 2975. APPARATUS FOR THE RECOVERY OF BROMINE. By C. H. COLLINGS. I. O'ject. THE daily routine work of a clinical laboratory includes the estimation of the urea percentage of urine specimens submitted for analysis. Such urea estimation is usually performed by means of the sodium hypobromite method, and in the course of (say) a year a considerable amount of hypobromite must be thus used and eventually emptied down the sink. As most chemicals now cost 100 per cent more than before the war, it appears to me possible that others may care to save their bromine and their pockets by means of a simple apparatus that I have devised to recover the bromine from used hypobromite. An essential feature about it is that it runs with the minimum of atten D according to the usual hypobromite formula, minus, of course, the bromine. Here they immediately combine with the NaHO, rapidly transforming it into the yellow hypobromite. So much for the principle of the thing. I will now give working details, adding for the sake of lucidity that the illustration is purely diagrammatic. The drawing is made as though the generator and receiver were both rolled out flat and the inlet and outlet tubes, &c., placed in a row instead of being, as in reality, grouped together. Beginning at the extreme left, air under the pull of the aspirator enters the conical glass, v, through the rubber tube leading into the two-bulb tube, emerging under the surface of the fluid, which consists of a solution of caustic soda. It bubbles up through this and passes on through the tube B and inlet tap into G. (A simpler form, such as F', can be adopted; that figured lends itself to easy disconnection when putting the apparatus away). A separating funnel, D, marked for 50 cc. and 100 cc., serves admirably for the successive introduction into G of hypobromite waste and commercial HCl. A loose tuft of cotton-wool retains casual fumes. E is a draw off syphon, closed by a tap at its outlet, to empty G when the HCI action is completed. F is an outlet tube controlled by a tap, and here we pick up the air current again, now charged with Br fumes. It passes on through the DIAGRAMMATIC ILLUSTRATION OF APPARATUS FOR THE RECOVERY OF BROMINE. tion and can be attended to by any capable laboratory-boy, thus excluding the need to calculate out cost of skilled labour contra market value of Br recovered. I will now describe the apparatus in detail, with concise instructions for its use. II. Apparatus. The illustration shows the apparatus set up and working. It consists essentially of a generator, G, connected by a delivery pipe with a receiver, R. The hypobromite waste should first be emptied into a big bottle in the laboratory and allowed to accumulate. It is then introduced into G and commercial HCl added. This displaces the Br from its combination, the Br rising above the fluid in characteristic brown red fumes. A current of air is drawn through the whole length of the apparatus by an aspirator (not shown) connected up at A. This carries the Br fumes into R and discharges them under the surface of a sodium hydroxide solution, made up delivery tube via r' into the receiver R. The inlet tube F' is also controlled by a tap, and its lower end lies beneath the caustic soda (hypobromite formula) contained in R. Here the Br fumes emerge and instantly combine with the NaHO to form sodium hypobromite, evidenced objectively by the initiation of a yellow tinge in the solution and its steady intensification of colour. D' and E' correspond in function to D and E, and need no further description. The air stream, now cleansed cf Br, finally emerges from R via B' on its way to the aspirator, which is connected up with the apparatus at A. It is necessary, to maintain an effective air-stream, to hermetically seal both bungs with paraffin wax. No leakage should be allowed anywhere. It is obvious, of course, that the function of v is to prevent any back-push of Br vapour into the air of the This undesirable event is effectually provided against, both mechanically and chemically. Any accidental leakage of bromine at other points can room. be promptly neutralised by the liberation of ammonium fumes from the o 880 bench bottle. III. Technique. Se up the apparatus, see to absence of leakage, connect the aspirator and start it. See that the inlet into v is below the surface of the liquid. Introduce into R through D' NaHO solution to well cover the bottom end of inlet tube F. Close D' tap. Open taps F and F', keeping tap c temporarily closed. Pour waste into D up to 100 cc.; run into G, close tap, pour commercial HCI into D up to 50 cc., run tnto G and rapidly close tap. Br fumes instantly rise from the mixed waste and HCl. Cautiously open tap c to full, and all is now under way. Pour 25 to 50 cc. more HCl into D and replace cottonwool. Run more of the acid into G from time to time as may be needed. Before admitting it, momentarily close tap c to stop back-rush. A very short time suffices to liberate all the available Br and to aspirate it into R. It is recommended to effect the Br separation in small portions; that is, after the quantity of waste named has been dealt with syphon it off from G before adding a fresh lot. It is now, of course, useless and not worth further preservation. To test whether Br is still being appreciably given off, close outlet tap F. Back pressure in v results if evolution is still going on. In emptying & of treated waste, if fumes are feared run the waste into a beaker or jar holding an inch or two of tap-water. The waste sinks at once in this, the water serving as a screen. The syphon tubes E and E' can be brought easily into operation in the first instance by connecting them up reThis suffices to respectively with the aspirator direct. fill each tube, which can then of course be kept full, ready for next time. A simple calculation will show the amount of waste needed to furnish sufficient Br for the quantity of NaHO solution in R, allowance being made for dilution of the waste by the urine and for a certain residuum ef Br still clinging to combination in G. NOTES IN REGARD TO TITRATION OF By C. R. GYZANDER, It seems to be a common practice in titrating free sul- The caustic soda solution used was about N/5, and contained a slight excess of BaO2H2 in order to ensure the absence of CO2 and its interference with phenolphthalein indicator. The acid used was C.P. sulphuric acid, of which 14 3675 grms. were dissolved in two litres of boiled and cooled CO2 free distilled water. The pipettes were of the normal variety, graduated according the Bureau of to the requirements of Standards. The accuracy of the burettes will be evidenced by the results obtained by them (Table I.). The end-point for lackmoid, methyl-orange, and dimethylamidoazobenzol appears to be identical under these conditions, and more sensitive than phenolphthalein, but all the indicators are nevertheless proportional to the amount of acid present. The slightly higher result for 10 cc. than what is proportional to the acid present is The lack of sensitiveness which my indicators exhibited under these conditions compared with those obtained by Glaser must be due to the composition of the indicators themselves, and goes to show that it is not permissible to take things for granted, but one must determine by actual experiment the relation existing between phenolphthalein and whatever other indicators are to be employed, under conditions similar to those of the actual analysis, if phenolphthalein was used in the standardisation of the caustic soda solution. So, for example, while it would be correct to use the titre established with phenolphthalein on a N/10 NaOH solution for any indicator, it would be wrong to employ 10 cc. portions of N/5 NaOH simply because all the indicators appear to act uniformly in such a case. The proper thing to do is to establish the titre on any of the larger amounts of solution which indicate a proportional difference between the indicators. As lackmoid, on account of its sharp change from red to blue, as well as its non-sensitiveness to carbon dioxide, makes the indicator par excellence for sulphuric acid, no other indicator should be employed in the titration of commercial sulphuric acid, but as the end-point with lackmoid comes earlier when using N/5 NaOH, the titre established by phenolphthalein must be changed in the ratio 68.4 68.2 100293 if the titrations are to be identical on iden tical samples, as of course they should be. As an example I offer the following analysis of a sample of oleum, which was free from SO, but contained a little ferrous sulphate, too small, however, to influence the results, practically speaking. Oleum-80434 grms. per litre, 50 cc. acid + 50 cc. water and 20 drops lackmoid required 42.9 cc. NaOH solution, approximately N/5. The exact titre of the solution, established with acid potassium phthalate and phenolphthalein, was 0.008077 grm. SO3 per cc. The lackmoid titre is therefore 0'008077 X 1'00293=0.008100 grm. SO3 per cc., and the results of the titration is NaOH are employed in establishing its titre, due to CO2 interference, and this is undoubtedly the major cause in the often large differences met with in practice when comparing results obtained on identical samples by different operators. Since few, if any of commercial or works laboratories are provided with constant temperature rooms, the rise and fall in the temperature of the standard solution with the temperature of the laboratory is not always a negligible quantity either. In the case of the solution quoted, its sp. gr. was 100867 at 15° C. and 100540 at 30° C. Change in volume in 100 867 = 100'32 expanding from 15° to 30° C. is therefore 1'0054 for 100 cc.; that is, the rate of change of volume with 0.32 temperature is X's 0 000213 cc. per cc. for change in the temperature. 100 ised and used at 28° C., a cooling to o° C. would involve a As the solution for the oleum test quoted was standardwhich amount the solution used at 20° should be corrected reduction of volume equal to o'000213 × 8 × 42'9 = 0.07, by if the results are to be correct. Neglecting this correction the oleum at 20° would appear to contain only(429-007) × 0.0081 × 20 X 100=86 26 per cent total SO3 8.0434 13'74×4'4438-61.06 per cent SO3 equivalent Free SO3=25.20 per cent, or a loss of o·76 per cent which might be avoided by proper allowance for temperature change. THE SEPARATION OF VANADIUM FROM PHOSPHORIC AND ARSENIC ACIDS AND FROM URANIUM. By W A. TURNER. In a previous paper the determination of vanadium when present in the form of a soluble vanadate has been described (Am. Fourn. Sci., 1916 [4], xli., 339). It seemed desirable to make use of this determination for separation Had we accepted the phenolphthalein titre we would of vanadium from some of the common impurities with have obtained That is, while we would have cheated ourselves by only 0.25 per cent on total acid by using the lower phenolphthalein titre, we would have underestimated free SO3 by 1.36 per cent, which is quite a noticeable amount, particularly if oleum is bonght and sold on the basis of free SO3. The determination of free SO3 is, however, not always as simple as in this case, since the presence of notable amounts of sulphates and of SO2 must be established before we may determine water of hydration by difference, or the results in free SO, would be too low. It is also evident that if the NaOH solution is not free from CO2, its titre, if established with phenolphthalein, will be the more incorrect (that is, too low) the more cc, which it is associated in nature. To this end separations from phosphoric and arsenic acids and from uranium have been attempted, and the following pages are a record of these experiments. In the separations from phosphoric and arsenic acids the procedure was exactly the same as in the simple determination of vanadium, with the exception that the precipitates required a more thorough washing. This procedure is briefly as follows: Portions of about 25 cc. of the metavanadate solution, accurately weighed, were diluted to about 150 to 200 cc. The amount of phosphate or arsenate indicated was added and enough sulphuric acid to make about 1 per cent of the volume. Cupferron (the ammonium salt of nitrosophenylhydroxylamine) was then added in 6 per cent solution with stirring until a slight excess was present, as shown by the appearance of a white precipitate of nitrosophenylhydroxylamine (formed when cupferron comes in contact with an acid solution). Two or three cc. in excess are added and the precipitate is filtered without delay and washed with a 1 per cent solution of sulphuric acid containing a little cupferron. The precipitate after being allowed to drain for a time on the filter is transferred to a platinum crucible, dried, ignited, and weighed as vanadium pentoxide. |