Microbomb for Determination of Organic Halogens FRED E. BEAMISH,University of Toronto, Toronto, Ontario, Canada
T
HE determination of the halogen c o n t e n t of or-
The determination of halogens in organic Cornby means of a sodium perozide-sugar fusion in a microbomb using milligram samples has been accomplished. The results obtained Over a wide range Of compounds, only a few Of which are published, indicate this method to be applicable to all organic halogens which may be determined in the standard macro sulfur bomb.
ganic means of a sodium p e r o x i by de fusion in a macrobomb is perhaps the most rapid and e f f i c i e n t general method known. Parr in 1908 ($1 discusses in a general Of the way the bomb fusion t o the determination of arsenical and p y r i t i c a 1 ores, copper, sulfur in rubber and silicon carbide, phosphorus, arsenic, sulfur, and halogens in organic compounds. The work by Lemp and Broderson, 1917 (I), as illustrated by their table of results, is somewhat incomplete. No attempt was reported to prove by experiment the explanations offered for discremncies in manv of the results obtained. The* bomb-fusion method for halogen determination has been in use under the author's supervision for two Years and except in a few cases has given very satisfactory results.
the bomb fusion replacing the distillation of halide in a hot tube by means of a current of oxygen (3).
The sample w a s p l a c e d i n a bomb with 0.5 gram of sodium peroxide and 10 mg. of lactose. These were thoroughly mixed and the flame from a small burner was applied for 30 seconds. It was found necessary to wash the precipitate with 100 cc. of nitric acid solution (1 to 100) in order t o remove all of the sodium nitrate. The results obtained were not consistently correct and would seem t o indicate that this method offers no advantage over the present micromethods. DETERMINATION USINGSEMIMICRO SAMPLES
It was then decided to determine the possibility of using the method for samples slightly larger than the strictly microsample.
PURENICKELBOMBCUPS
The sample, which must be dry and finely divided, is so adjusted that the weight of silver halide obtained will be between Bombs of various metals have been used, but the stainless- 25 and 40 mg. One and one-half grams of sodium peroxide and steel and the pure nickel bomb cups were found to be most 30 to 40 mg. of powdered lactose were used as the fusion mixture, suitable, Fusions from pure nickel cups have a decided ad- and were well mixed by shaking thoroughly. cap with the gasket, which must not be pitted, is placed vantage over those from stainless-steel cups. The solution in The position. The bomb is held in a small vise with lead-lined of the fusion is water-white and the corrosion is much less in jaws and the clamp tightened with a wrench or pliers. A small the nickel cups. The loss of weight as a result of 10 fusions flame is applied for 30 seconds and the bomb is allowed to cool for a few minutes in air and then dropped into a beaker of distilled water. The bomb is again placed in the vise and the clamp l o o s e n e d . The cap is removed with a small pair of pliers and the under part washed into a test tube of 35 mm. inside diameter and 155 mm. inside length, preferably FIGURE 2. TUBE with a lip to simplify filtering. The test tube is of course provided with the usual microstand. The bomb proper is then placed in a suitable wire loop. It is advisable to use 8 noncorrosive wire, such as pure nickel. The outside of the bomb is washed off thoroughly with distilled water, lowered into the test tube, and placed on its side. The bomb is partially covered with water and the test tube covered with a watch glass. If the reaction does not begin immediately, it may be started by holding the test tube in hot water. After the reaction has ceased, the watch glass, the wire, and the wall of the test tube are washed down with water, hot in the case of chlorides and cold with bromides and iodides. The bomb is lifted by means of the wire and the whole carefully washed with I' I1 water. The bomb proper must not be handled with the hands 1 k-13 mm.4 I and when not in use should be kept in a closed container, which -16 mm.+ may be made from a small box fitted with a block of wood having holes of the same diameter as that of the outside of the bomb cup. FIGURE 1. DIAGRAM OF MICROBOMB At this stage the liquid in the test tube should not occupy more 15 to 20 cc. In the case of bromides and chlorides, conin the stainless steel cup was 92.4 mg., whereas the loss of than centrated nitric acid is added cautiously until the solution is weight as a result of 10 fusions of the same substances in the slightly acid. 3 cc. should be sufficient. In the case of iodides a solution of nitric acid diluted 3 to 1 is added. The bubbles nickel cup, conditions being about the same, was 6.7 mg. may be removed by stirring. The solution is now filtered into a DETERMINATIONS USINGMICROSAMPLES AND A MICROBOMBsecond test tube, of the same dimensions as the first, through a 10-cc. Gooch crucible, which i? fitted with a disk of good grade It was decided to investigate the possibility of using a small filter paper in place of the customary asbestos. This preliminary bomb for the determination of halogens in microsamples of filtering is accomplished with suction and a convenient arrangematerials. The bomb used in this work, illustrated in Figure ment is to place the test tube in a large-mouthed bottle fitted with a two-hole rubber stopper. The Gooch is fitted into a tube, 1, was made by the Burgess-Parr Company, Moline, Ill., the farther end of which dips into the slanting test tube in order of stainless steel. The apparatus used was the standard to avoid splashing. This atering may be accomplished in 5 equipment for microgravimetric halogen determination with minutes. The sides of the test tube and the Gooch are washed 348
September15,1933
INDUSTRIAL AND ENGINEERING
down, and finally the washings are tested to insure complete absence of halides. The tube containing the halide solution, the volume of which should be about 40 cc., is removed from the bottle and an excess of 0.1 N silver nitrate solution added. The precipitate is coagulated in all cases by vigorous stirring by means of a stirring rod, the end of which has been drawn to a dull point.
CHEMISTRY
The procedure followed with the macromethod is essentially that described above; standard macroapparatus is of course used, and the size of the samples so adjusted that the weight of silver halide will be between 225 and 275 mg. Larger samples have been used but are not to be preferred.
PREPARATION OF CRUCIBLE AND TREATMENT OF PRECIPITATE The standard 10-cc. Gooch crucible was used throughout and found to be satisfactory. A smaller crucible if desired may be made by cutting off the top of the 10-cc. Gooch. Because of the small weight of the precipitate it was found advisable to prepare the Gooch in the following way:
-
Full suction is applied and a thick mass of suspended asbestos sufficient t o form a layer about 3 mm. thick is added. The whole is macerated with a fine stream of distilled water and sucked dry, washed well with a hot chromic solution and hot concentrated nitric acid and then water, and tapped down with the blunt end of the stirring rod. The asbestos is then washed with 95 per cent alcohol, dried in an oven at 140” C. for 25 minutes, cooled on a copper block in a desiccator for 10 minutes, and allowed to stand in the balance for 15 minutes. The precipitate of silver halide is filtered into the prepared Gooch by means of the ointed stirring rod. The test tube is washed finally with alcoiol to insure complete removal of the silver halide and any adhering particles are removed with the feather. The precipitate is washed with 150 cc. of water, to insure complete removal of the nitrates, and then with a little alcohol, dried at 140” C., cooled and weighed as indicated above. The precipitates may be weighed on a good macrobalance but the samples must of course be weighed on a microbalance.
TREATMENT OF LIQUIDS The most satisfactory method of weighing liquids is by means of tubes prepared in the same way as the usual microtube (4). This method has also been used in the macroscale and gives good results. The semimicro glass tube should weigh not more than 20 mg. The macro tube should weigh not more than 90 mg. The tube found most suitable is illustrated in Figure 2. I n all cases the tube should be centrifuged to remove the liquid from the capillary and then sealed. The tube is placed a t the bottom of the microcup and covered with the peroxide-sugar mixture and the cap is locked in position. Good results were obtained without shaking the tube with the peroxide-sugar mixture or b,reaking off the capillary before placing the tube in the bomb cup.
TREATMENT OF IODIDES Iodides require a slightly different procedure. Before acidifying with nitric acid, a few cubic centimeters of nearly saturated sulfur dioxide solution are added and, if upon addition of the nitric acid the violet color of free iodine appears, more sulfur dioxide solution is quickly added. The acid solution is filtered immediately and silver nitrate solution is added. The further treatment is that of the chlorides and the bromides. Blanks on all reagents must be carefully determined. This method was found to apply over a large range of organic compounds and Table I shows a few results obtained on some of the organic halogen compounds employed. TABLEI. HALOGEN CONTENT OF COMPOUNDS ANALYZED SUBSTANCB
Calculated
%
p-Dichlorobenzene
48.25
Dichlorophenol
43.52
Bromocamphor
34.59
Dichloraniline
43.78
Dibromobensene
67.76
p-Iodoacetanilide
48.63
Bromobenzene
50.91
m-Dichlorobenzene
48.25
HALOGEN Macro
%
48.16 48.15 43.41 43.45 34.58 34.53 43.77 43.80 67.70 67.84 48.16 48.12 50.78 50.86 47.99 48.11
Semimicro
%
48.19 48.33 43.55 43.54 34.56 34.56 43.73 43.83 67.59 67.69 48.22 48. OS 50.78 50.86 47.95 48.06
349
SUMMARY
The halogen content of organic compounds may be determined by means of sodium peroxide-sugar fusion in a microbomb with about the same degree of accuracy and as rapidly as the macromethod. The weight of the sample required for analyses is much smaller than that required using the macromethod. The method is applicable to all compounds which may be determined by means of the macromethod, and has the decided advantage that if the above directions are followed a destructive explosion is eliminated. Compared to the microgravimetric method the determination of organic halogens is completed much more rapidly and is somewhat more accurate. ACKNOWLEDGMEKT The author is indebted to F. Bremner and A. Kaellgren for checking results of analyses. (1) Lemp and
LITERATURE CITED Broderson, J . Am. Chem. Soc., 39, 2069 (1917).
(2) Parr, 8. W., Ibid., 30, 764 (1908). (3) Pregl, F., “Quantitative Organic Microanalysis,” 2nd ed., pp. 123-36, J. & A. Churchill, London, 1930. (4) Ibid., p. 70. RECEIVED June 3, 1933.
Ground-Glass Junctions HARLANL. BAUMBACH University of California at Los Angeles, Calif.
THOSE
who have tried to make ground-glass junctions by grinding a tapered portion of a glass tube into a flanged end know that it is impossible to procure an evenly ground job, At any one time only a very narrow strip about the circumference is in contact. By using a hollow cone made of 0.03-inch (0.75-mm.) thick sheet copper one can grind each piece separately and then place the two together for a slight final grinding if necessary. The inside of the cone is used for the grinding of the taper and the I outside for t h e g r i n d i n g of the I socket. The sheet copperls cut as shown in Figure 1, bent in the form of a cone, and soldered end to end. Standard dimensions c a l l f o r a n increase of 0.15 cm. in diameter for F I G u R E 1 . every 1 cm. measured along the axis SHEET COPPER of the cone. The cone can be mounted for the grinding by means of a one-holed rubber stopper and a 0.19-inch (5-mm.) wooden dowel placed in the chuck of the lathe or drill press. Turpentine or water is applied either to the copper or to the I h m R E 2 glass and powdered silicon c a r b i d e is a d d e d . This operation is repeated until the grinding is of the desired depth. Copper is used in such grinding operations because it is extremely tough, yet soft enough to let the fine particles of carborundum imbed in it and grind away the glass. By using a hollow cone of copper the same slope is assured for the taper as for the socket,
d-J
RECEIVED July 24, 1933.
