ANALYTICAL EDITION
RIAY 15, 1910
Summary The equivalent weights of salts can be determined from samples as small as 0.3 mg. by the application and modification'of the Adair and Keys electrodi&is method for total bases in biological fluids. When the procedure was carefully folloIved, values obtained for the equi17alents mere rarely Over 3 per cent from the theoretical values. A simple method for
299
the preparation of sintered-glass membranes is described. An efficient method for dividing mercury into a very fine 'pray is mentioned.
Literature Cited B., J . Bid. Chem.. 114, 449-59 (1936). (2) Kirk, p. L.,Craig, R., and Rosenfels, R. S., ISD. ENG.CHEAI., Anal. Ed., 6 , 154-5 (1934).
( 1 ) Keys, A.
Bomb for Determining Organic Chlorine by Lime-Fusion Method WILLIAM M. MAcNEVIN AND WILLIAM H. BAXLEY, Ohio State University, Columbus, Ohio
T
HIS paper describes the construction of a simple closed
metal tube or bomb and its use in a semimicro modification of the classical, but little used, lime-fusion method (2) for the determination of organic chlorine. The investigation was undertaken to find a method for determining organic chlorine which would require only simple and easily attainable apparatus and a t the same time would be as rapid as any of the new methods now in use. Investigation of the literature (2) on the various methods for determining organic chlorine revealed that the chief limitation of the classical lime-fusion method which was always conducted in a n open glass tube, was that easily volatile samples escaped before reacting with the calcium oxide. The results mere therefore often low. This, together with the requirement of a large amount of calcium oxide in each determination, is considered to be the principal reason for lack of general popularity of the classical method. Recently it has been shown in this laboratory (1) that if a closed metal tube is used, easily volatile organic fluorides are quantitatively decomposed by heating with calcium oxide. It has therefore seemed logical to apply this principle to the determination of the other halogens in organic combination.
Apparatus The bomb consists of a hollow cylinder of cold-rolled steel open at one end and of the approximate dimensions shown in Figure 1. The open end is flanged and may be closed by a combination of threaded collar, A , and plug, B. ( A and B are standard brass fittings used in the refrigeration industry and may be obtained from any refrigerator supply house. The hollow cylinder can be turned from a bar of cold-rolled steel. Exact dimensions do not appear important. Most laboratory supply houses are also able to provide the complete assembly.) A soft copper disk placed betiveen plug B and the inner flange of the neck of the bomb serves as a washer and provides a tight fit. (Cold-rolled sheet copper may be softened by heating t o near redness and quenching in water.)
,
I"
,
COIL
FIGURE 2. INTRODUCTION OF SOLIDSAMPLE INTO BOMB
A long-stemmed weighing tube > of the approximate dimensions indicated in Figure 2 is required for introducing solid samples into the t I" 1 bomb. Liquid samples are drawn Scale UD in oreviouslv weighed thinGalled glkss bulbs"(Figure 3) which FIGURE3. SAMPLE are then sealed off. BULBFOR LIQUIDS Porcelain Gooch microcrucibles with asbestos mats have been used for filtering the silver chloride. They have sufficient capacity for amounts of precipitate up to 130 mg. Wlien used with the Wintersteiner filtering microapparatus ( S ) , the process of filtering and drying the precipitate requires not more than 25 minutes. The balance used in this work was an Ainsworth of semimicro type, with a sensitivity of 0.05 mg. per division of the pointer scale. The weights were calibrated tjo the nearest 0.01 mg. All weighings were made to the nearest 0.01 mg.
Plug 6
Reagents Calcium oxide was prepared by heating analytical reagent quality calcium carbonate at 900" C. for 2 hours, and after cooling was stored in a desiccator containing Drierite. The diameters of most of the particles ranged from 5 to 10 p . About 1.5 grams are required lor each determination. The nitric acid, silver nitrate, and potassium nitrate were of analytical reagent quality. Distilled water free from chloride was used for preparing all solutions. Several blank determinations with usual amounts of all reagents failed to show any trace of chloride as indicated by turbidity after 24 hours' standing.
FIGURE 1. HIGH-TEMPERATCRE C.4LCICM OXIDE BOMB
Procedure The bomb is cleaned by washing with water and acetone and drying in a blast of air. Calcium oxide is added until the bomb is about one-third full (Figure 1). Enough sample to give not less than 8 mg. of silver chloride is introduced by means of the
Sample \
.
I1
I
The bomb is sealed by turning plug B into collar A and is conveniently done by clamping A in a vise and using a wrench to tighten B. The bomb is clamped to a ring stand in a horizontal position and is heated with a Pittsburgh or Pvlkker burner. A metal screen is placed between the operator and the bomb because of a remote possibility of an explosion. However, on no occasion has there been any evidence of dangerous pressure durin heating. Observation of the bomb while heating is accomplishei by the use of a small mirror standing a t the brick of the desk or hood.
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I
Copper Washe:
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Scala
Collar A
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I
INDUSTRIAL AND ENGINEERING CHEMISTRY
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TABLE I. DETERMIN~TION OF ORGANIC CHLORINE
Sample hlonochloroaoetio acid. CnH OZCl
8-I-IydroxStrichlorobutyric
acid, CIHsOsCL
COUP bus- Weight tion of Period Sample .Win. 5
10 15 20 20 20
20
Mg.
Mg.
12.38 14.38 13.49 8.38 35.43 27.69 18.44 20.39 12.09 8.78
18.40 21.80 20.55 12.66 53.58 57.55 38.53 42.57 11.12 8.13 7.03 10.01 10.04 7.75 23.18 8.23 13.15 8.26 131.31 52.21 20.63 31.38 9.25 11.51 14,79 11.61 42.21 39.52 47.65 30.06 32.34 37.05
8.85
p-Xitrobenzyl chloride, CiHsOzNCl p-C hloronitrobenaene, CsH40nNC1 Carbon tetrachloride, CCh Tetrafluorotetrachloropropane CsClrFr Tertiary butyl chloride, CrHgCl a-Chloronaphthalene, C!oHiCl p-Dichlorobenzene, CsHaClz
He.xachlorobenseiie,CeCh Research compounds CieH~sOizCl
20 20 20 20 20
20 2n -"
20 20 20 20
20 20
20 35 ~. 20 20 20 20
Weight of AgCL
11.80 11.92 9.25 2s,14 9.77 14.54 9.07 35.33 13.93 9.05 13.82 5.98 7.45 16.93 13.17 22.51 20.78 24.38 15.35 10.68 12.25
20 20
44.65 40.79 13.49 12.23 12.10 5.28 18.96 8.27 Cw HitOzCI? 19.61 13,so 26.36 18.91 40 30.39 21.54 20 27.06 19.21 0 100 mg. of KOHl were added t o calcium oxide. Ci~HisOiCl
20 20 20 30
~1 Calcd.
% 36.77 37.50 37.68 37.37 37.41 51.41 51.69 51.65 22.91 22.75 19.65 20.99 20.84 20.73 20,3s 20.84 22.37 22.53 92.71 91.94 56.39 56.17 38.26 38.22 21,61 21.81 46.39 47.05 48.35'3 48.44" 74.91a 74.820 7.42a 7.47a 10.79 10.79 17.41 17.75 17.53 17.56a
CI The,,retical
% 37.53
51.26 22.95 20.90
20,66 22.51
92.20 55.S7 38.30 21,80 48 22
74.71
'." 10.93 17.50
weighing tube. More calcium oxide is added until after gentle tapping on its bottom end, the bomb is about two-thirds full. The copper washer is put in place, the various parts of the bomb are assembled, and B is turned tightly into A . The contents of the bomb are well shaken, after which the bomb is again tapped to settle the mixture toward the bottom end. It is then ready for heating. The lower two thirds of the bomb is heated to dull redness over a burner for 20 minutes. After cooling under the water tap, the bomb is opened and inverted over a 250-ml. beaker containing 50 ml. of water, and the contents are removed by gentle tapping. Traces of calcium oxide which adhere to the walls of the bomb are removed by rinsing several times with small amounts of hot water. The covered beaker with contents is kept cool in a pan of water and concentrated nitric acid is added until the solution is acid: usually 3 to 5 ml. are sufficient. The solution is filtered through filter paper to remove carbon and the a t e r is well washed with hot water. The volume at this point should not exceed 125 ml. One milliliter of 5 per cent silver nitrate is added slowly with stirring and the precipitate is coagulated by heating nearly to boiling. A test for complete precipitation is now made by adding another drop of silver nitrate solution. After cooling the solution in an ice-water bath to about room temperature, the precipitate is filtered on a weighed Gooch microor semimicro crucible with an asbestos mat. Fifty milliliters of 0.5 per cent nitric acid solution are used in small portions for washing. A policeman is used t o remove traces of adhering precipitate. The precipitate is dried to constant weight at 225" t o 250" C. If microcrucibles are used, 10 minutes' heating is sufficient. For liquid samples, the sealed bulb containing the unknown is placed between the t w o layers of calcium oxide. Shaking is of no value in this case, since the sample can escape only after the bulb has burst on heating.
Discussion The results of the analysis of fifteen organic compounds of widely different nature are given in Table I. All samples used were tested for purity by observing some indicative
YOL. 12, h O . 3
property such as melting or boiling point. In general the accuracy obtained is sufficient for the organic chemist, who is usually interested in determining the number of chlorine atoms in a molecule. The results with monochloroacetic acid and with p-chloroacetanilide show that less than 20 minutes' heating t h e is insufficient. Three nitrogen compounds were included in the group of compounds analyzed in order to see whether cyanide formation might lead to appreciable errors. Apparently it does not. The results for the four volatile liquids are in excellent agreement with the theoretical and indicate the advantage of using the closed tube rather than the open tube of the earlier workers. The technique of handling liquid samples is considered important. By sealing the bulb containing the sample, the escape of vapor is prevented until the calcium oxide has reached a fairly high temperature. Only then is enough pressure generated within the bulb to burst it. Some unburned carbon is always left and has to be filtered from the nitric acid solution of the oxide. I n most cases this carbon does not retain any chlorine. However, the authors' results indicate that whenever more than one chlorine atom is attached directly t o a benzene ring, it is difficult to remove all of the chlorine without the use of an oxidizing agent. The addition of about 100 mg. of potassium nitrate to the bomb has been found to oxidize the carbon sufficiently so that satisfactory chlorine values are obtained. Consequently, addition of potassium nitrate is recommended in every case where the condition of the halogen is unknown or where the ratio of carbon to chlorine is high. The outstanding difference between this method and that of Carius is in the comparatively short time required to obtain a result. For a single determination about 1.25 hours are required. If two bombs are available and several determinations are made, the average time may be cut to 50 minutes. When this method is compared with that using the Parr bomb, the principal differences are: (1) the bomb may be assembled a t a relatively small cost; (2) decomposition is attained by using a higher temperature with no, or a t most a trace of, oxidizing agent; (3) the reagents are comparatively easier to keep and are less dangerous to handle; (4) less pressure is generated than in the Parr bomb, and the bomb is therefore easier to seal. The application of this high-temperature calcium oxide bomb to other determinations is in progress in this laboratory.
Summary
A simple bomb has been constructed for carrying out the decomposition of organic chlorides by the limefusion method. The satisfactory determination, on a semimicro scale, of chlorine in fifteen organic compounds including four liquids is described. The use of a closed metal tube instead of an open glass tube as formerly used extends the application of the lime-fusion method t o volatile liquids. The bomb is recommended in organic elementary analysis for the determination of chlorine in preference to the Carius method, especially where time is an important factor.
Literature Cited (1) H e n n e , 4 . L., a n d Renoll, M. W., J . Am. Chern. S O C . , 61, 2489
(1939). (2) Meyer, H., "Analyse und Konstitufions-Ermittlung organischer Verbindungen", p. 167, Berlin, Julius Springer, 1938. (3) Wintersteiner, O., Mikrochemie, 2, 14 (1924). TEISwork w&s done in partial fulfillment of the requirements for the degree of master of scienoe a t The Ohio State University.
