Stabilization and Stability Tests of Cellulose Nitrates E. BERL, G. RUEFF,
AND
CH. C.iRPENTER, Carnegie Institute of Technology, Pittsburgh, Pa.
periments 6 and 9. It is remarkable that No. 5 also gives a rather high ignition point as compared with No. 3 because, with the addition of the wetting agent, the aqueous hydrochloric acid could wetthe fiber. Of great importance is the sulfuric acid content after the treatment, expressed in percentage of sulfur trioxide. The best result is obtained by experiment 4. Nos. 6, 7, 9,10,and 11 show that the amount of bound or strongly adsorbed sulfuric acid is decreased below 0.1 per cent of sulfur trioxide in the material. (The sulfuric acid was determined by alkaline saponification of cellulose nitrate with sodium hydroxide free of sulfates, oxidation compounds with pure hydrogen peroxide, Of the lower acidification, and precipitation of the sulfate with barium chloride. This method is described in Berl-Lunge, 6.)
HE stability of explosives, especiall~7of cellulose nitrates, is of the greatest importance. several experimentsare
T
described below which show how by different stabilization treatments the nitrogen content of cellulose nitrates, their viscosity, the ignition point, and their sulfuric acid content, expressed in percentageof bound sulfur trioxide are affected by different treatments. Table I indicates that, in many cases, the nitrogen content is decreased by certain stabilization treatments, Jvvhilein other cases it is increased. Experiments 6, 7 , 9, 10, and 11 show an increase in the nitrogen content because unstable material with lower nitrogen content has been eliminated. In most cases the viscosity of the cellulose nitrates is decreased. An increase in viscosity could be observed only in experiment 9, which show that the treatment does not involve a degradation of the cellulose nitrate. The ignition point is raised in all cases, but in experiments 1, 2, and 3 the increase is small and these treatments show practically no elimination of those substances which cause the instability. It is remarkable that for the treatments with distilled water (No. I), with a weak base alone ( Y o . 2), and with a weak acid alone (No. 3), the stabilization effect is rather poor. No. 4 is a combination of experiments 2 and 3, and gives a good stabilization effect. The highest ignition points are obtained in ex-
Stability Tests In the literature many tests are described for determining the stability of cellulose nitrates and other explosives. They may be divided into qualitative, semiquantitative, and quantitative tests. Other tests are described which depend upon measuring the decrease in viscosity. QGALITATIVE TESTS: Potassium iodide (1, 13); zinc iodide (15, 23, 30, 41). Diphenylmnine (21, 27). m-Phenylenediamine (4). a-Naphthylamine (f7). Methyl violet (f2,36). Rosaniline (36). Lacmoid test a t 108.5'C. (4.9);at 132'C. (7). SEMIQUANTITATIVE TESTS: German test at
TREATMENT TABLEI. EFFECTOF STABILIZATION Sitrogen Before After Treated Twice, treattreatThree Hours Each ment ment
1 Distilled H20. 1000 c.
%
%
12.6
12.55
Logarithm of Relative Viscosity Before After treattreatment ment 1.7
1.65
Ignition Point (Corr.) Before After treat- treatment ment
c.
C'.
135
141
so3
Content Before After treattreatment ment
%
%
0.68
0.60
2 0.02 N NaHCOs,
HzO. looo C. 13.3 13.15 3 0.1 N HCI, Hz0, 1000 c. 13.3 13.25 4 0.1 N HC1, 0.02 N NaHC08, 1000 c.,100 hours 13.47 13.36 5 0 . 1 N HC1 2% agent,wetting HtO, 1000 c. 12.7 12.65 6 50%CHaCOOH 7 CHsCOO13 4 13.55 x a 2, 17~50 C. 7 0.1 NHzSOi 4CHsOH, 65' C. 13.3 13.5 8 O . l N H , Sl oOl oa +c. 1 3 , 3 CHIOH, 9 0.1NHCl CHJOH, 66O C. 13.4 13.55 10 0.1 N HC1 CHsOH, l o l o c, 1 3 , 3 13,55 11 0.1 AV HsPO4 CHsOH. 65' C. 12.6 12.8
+
+
+ + +
2.3
1.85
136
140
0.63
0.56
2.75
2.5
136
141
0.63
0.50
1.32
0.54
157
185
0.31
xone
1.7
1.7
156
186
0.68
0.26
1.83
1.45
126
190
0.63
0.09
2.3
2.1
136 136
188 188
0.63 o,63
0.08
1.8 2,35
1.93
125 136
190
0.63 o,63
0.04 o,oo2
1.7
1.56
136
186
0.67
0.03
2,3
219
o,ls
98' C . with phen lenediamine (29). pH determination (22, 32). 8onductivity (32, 34). S ectroscopy (40). Ultraviolet light (8, 10). gilvered vessel test (24, 28, 43, 47, 50). Warm storage (31). Loss in weight (14, 37, 45, 48). Development of heat (8). QUANTITATIVE TESTS: Will test (6, 39, 51). B ~ test (s). ~hlanometer method ~ (9, 1.4, 16, 18, 20, 25, 86, SS, 35, 38, 40, 46, 53). DECREASE IN VISCOSITY (4, 11, 19).
The following factors seem to be important
for a scientific stabilization test: 1. Determination of the whole decomposition curve o r an important part of it. 2. Use of only small amounts of explosives, so that an explosion is not dangerous. 3. The products of decomposition must remain in contact with the explosive, otherwise one gets a wrong picture. 4. The material to be tested should be in the same condition as is used later on. Therefore, the test should be made with cut or uncut cellulose nitrate, o r with dense smokeless powder, depending on conditions of use. The action of the nitric oxides depends on the external conditions of the material. 5. The test has to be carried out in the presence of oxygen. Thereoxidation of NO to N20,-
~
~
VOL. 10, NO.4
INDUSTRIAL ,4SD ENGINEERING CHEMISTRY
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(NO2) according to 2 N 0
+
Ot = N20,is quicker than by
+
the reactions NO 2HNOa = 3N02 H 2 0 and 3N0 = NO2
+6.NzO.+During the test the teni-
II=
n
33
fli
perature has to be constant bemuse of the high temperature coefficient of the reaction. The reaction speed doubles with a 5” C. increase in temperature. 7. The material must be completely dry, because water acts as a positive catalyst through saponification of the cellulose nitrate.
S e v e r a l y e a r s ago Bed and Kunze (5) described a semimicrochemical stability test which is, in fact, a n improved Will test (62). It used about one-Bth or onetenth of the amount of cellul o s e n i t r a t e used in the original Will test. T h e a u t h o r s b e l i e v e that both F tests h a v e certain weak points because they continuously remove the products of decomposition f r o m t h e E c e l l u l o s e nitrate in decomDI.IGRAM O F FEATHER h l . I N O M E T E R FIGURE 1. position and therefore give a somewhat inaccurate picture. Furthermore, they describe The piece of apparatus in the the decomposition only during and after a rather short time heater and extending up to the interval (see points 1 and 3 above). ground-glass joint, 3, is called the “ f e a t her m a n 0 me t e r ” The hollow, slightly curved, thin glass Glass-Feather Manometer membrane with the long needle, B , attached,to the top is called the I n the new stability test, advantageous use is made of the “feather. When preparing t h e f e a t h e r so-called glass-feather manometer described by Schaeffer and manometer for an experiment, Treub (&). This is shown in Figure 1. (The glass-feather tube 1 is open and extends up to manometer is made by F. E. Donath, 22 Fourth St., Aspinthe tip of the needle. The material to be tested is placed in the wall, Pa.) bottom of 1 and the feather manometer is then connected to the vacuum pump by means of the ground-glass joint, 9, and the tube, 10. Rubber pressure tubing is used to connect 1 and 10. When the necessary 1000 vacuum is produced in the feather manometer, 1 is sealed. The feather manometer is placed in the heater and connected to the mercury manometer system, which is then evacuated. The cross hairs of a rigidly mounted telescope are made to coincide with the tip of the needle. When pressure is produced inside the feather, the tip of the needle moves to the left. The pressure inside the feather can be determined at any time by adjusting the pressure outside the feather so that the tip of the needle again coincides with the cross hairs of the telescope. F is used to produce small changes in pressure outside the feather. Care w must be used in handling the feather manometer, since the feather will stand only about 200 mm. Hg difference in pressure.
.
Effect of Stabilization Treatments
FIGURE 2. EFFECTOF TRACESOF MOISTUREON DECOMPOSITION CVRVES 0.0500 gram of stabilized guncotton, dried over P2Os. 1 3 5 O C. (uncorrected). 532 mm. air pressure a t 2 5 O C. 1. Moisture removed through heating a t looo C. under vacuum for 10 minutes or by vacuum for 16 hours a t r o o m temperature 2. Containing moisture adsorbed during manipulation
For stability tests the authors use 5 or 50 mg. of cellulose nitrate in the absence or presence of air. Because of the very low weight of the explosives, if necessary, the rather high temperature of about 157” C. can be used without difficulty or danger. A very important point in this and other tests is the :preparation of the sample. The material to be investigated must be com-
APRIL 15, 1938
AXALITICAL EDITIOX
22 1
S204(S02), which again burns parts of the organic substance and is reduced to nitric oxide. This reacts again with the newly formed nitric acid. This process goes on until practically all the organic substance is burned by nitrogen peroxide, which finally is converted into nitric oxide, nitrous oxide, and nitrogen. Then the atmosphere becomes clear. On opening the feather manometer, the brown color returns, showing that nitric oxide has been formed. The nitrogen peroxide is the real catalyst which is responsible for the S-curve representing the autocatalytic decomposition reaction. This can be seen from Figure 9. The normal decomposition of cellulose nitrate took place. When about 50 per cent of the reaction had occurred, the gases were removed and the heating was continued. The break in the curve indicates that the observed pressure curve lies below the pressure curve expected, showing clearly the strong influence of the nitrogen peroxide.
FIGURE 3. EFFECTOF TRACESOF MOISTURE ON DECOMPOSITIOK CURVES 0.0500 gram of nitrated linters, 11 per cent nitrogen, stabilized, dried over PtOb. 135O C. (uncorrected). 532 mm. air pressure a t 25' C. 1. Moisture removed through heating a t 100" C. under vacuum for 10 minutes 2. Containing moisture adsorbed during manipulation
pletely dry. Drying the sample over phosphorus pentoxide is not completely sufficient because, during the handling of this dry material, i t quickly absorbs water from the atmosphere and gives inconsistent results. Figure 2 shows the difference in the decomposition curve of a guncotton if the material to be investigated is dried over phosphorus pentoxide and if this material, before sealing it in the glass-feather manometer, has been heated at 100" C. in a high vacuum for 10 minutes, or has been kept in high vacuum at room temperature for more than 16 hours. Figure 3 shows another experiment of this kind with a collodion wool which absorbs more water than guncotton. From Figures 4 and 5 one can see that the method gives TIME IN HOURS very reproducible results. The figures show the decomposiFIGURE 4. REPRODUCIBILITY OF DECOMPOSITION CURVES tion of different, completely stabilized samples, one investi0.0050 gram of guncotton nitrated with sulfuric a n d nitric acids and gated in vacuum a t 157" C., the other in air a t 135" C. water. 157' C. (uncorrected), In vacuum Fieure 6 shows the effect of washing unstabilized guncot&. Curve 2 shows the effect of nyashing with weak alkaline tap Fater and curve 1, with distilled water. The formation of a calcium salt of the sulfuric acid present as such, or in the form of a mixed ester, gives a higher stability. Figure 7 shows the curves which were obtained in vacuum with unstabilized and staX W bilized guncotton at 157" C. (uncorrected). Figure 8 shows a very interesting effect. The cellulose nitrate was decomposed in high vacuum. I n spite of the absence of oxygen, a brown gas is observed which is converted after3 wards into a colorless gas. The brown gas is Y) Y) nitrogen peroxide which plays an important g700 role in the decomposition process. It is this nitrogen peroxide which acts as an autocatalyst. It is formed first by a slight saponification of the cellulose nitrate. The nitric acid formed oxidizes the organic part of the cellulose 5 nitrate and is reduced to nitric oxide. Through i destruction of the organic part of the nitric FIGURE 5 . REPRODUCIBILITY OF DECOMPOSITION CURVES acid ester, new amounts of nitric acid are set 0.0500 gram of guncotton nitrated with sulfuric and nitric acids and water. 135' C. free. They react with nitric oxide to form 532 mm. air preasure at 25" C.
t 1
222
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FIGURE8. COLOR O F DECOMPOSITIOX GASES 0.0050 gram of stabilized guncotton. 1 5 i o C. (uncorrectedL6 Colorless gas becoming b r o a n on admitting air or on standing a t 22 C. for 2 4 hours. Fibrous, orange-brown residue. O n standing 24 hours becomes amorphous and dark
FIGURE 6. EFFECTO F WATERWASHESO S DECOMPOSITION CERVES OF UNSTABILIZED GUNCOTTON 0.0050 gram of guncotton nitrated with sulfuric a n d nitric acids and water. 128' C., in vacuum
FIGURE9. EFFECTOF REXOVAL OF DECOYPOSITION GASES 0.0060 gram of stabilized guncotton. 157O C. (uncorrected), in vacuum. Experiment interrupted and gaseous decomposition products removed. heating then continued
FIGURE7. DECOMPOSITION CURVES 0.0050 gram of guncotton nitrated with sulfuric and nitric acids and water. 157' C. (uncorrected), in vacuum 1. Unstabilized, washed with t a p water 2. hlcohol-stabilized
Figure 10 shows a decomposition curve for unstable and stable guncotton obtained with 5 mg. and at such an air pressure a t room temperature that a t 135' C. the air pressure was just 1 atmosphere. All these curves give a n integration of the results. The differentials give a somewhat clearer picture. Figure 11 indicates the pressure differences which occur during the same time intervals. Unstabilized guncotton, 1, shows an enormous decomposition at the very beginning which quickly slows down. The stabilized guncotton, 2, shows the maximum of changing pressure after the 32nd hour.
Improved methods of stabilization allow the production of completely stable cellulose nitrates without puiping this material. It is known that the pulping process needs time and power. With the right stabilization, one can get exactly the same stability with unpulped as with pulped material, as can be seen from Figure 12. Finally, Figure 13 shows the stabilities which can be obtained with cellulose nitrates made by different methods of nitration. Guncotton was made by nitrating cellulose with a sulfuric acid-nitric acid mixture, with a mixture of nitric acid and phosphoric acid, and with nitric acid and glacial acetic acid. The stabilities of the three different nitrates are practically the same.
Conchsion The feather-manometer test which works with 5 or 50 mg. of cellulose nitrate a t elevated temperature gives a very interesting and complete insight into the processes which take place if any cellulose nitrate, or other explosive, is heated a t temperatures between 135" and 157" C., or higher. These tests can be carried out without endangering the experimenter. They have the great advantage that all decomposition products remain in contact with the cellulose nitrate, so that these may be considered rather severe tests. Cellulose nitrates which are found very stable with the new feather-manometer
.kPRIL 15, 1938
ANALYTICAL EDITION 30b c LI
2 I
-
E200 -
2 =I
2
1
In
w
v)
a 0.
z w
v)
\
100
2 a U
z v I
I
FIGFRE10. DECOMPOSITIOS CCRTES Beginning a t atmospheric pressure, 1 3 3 O C. 532 mm. air pressure a t room temverature 1. 0,0050 gram of unstable guncotton 2 . 0.0050 pram of same guncotton, stabilized
FIGURE 11.
PRESSURE CH.4XGES WITHIN 2 1. Unstabilized 2. Stabilized
HOKIR~
test are also found very stable with the Bergmann-Junk test, in spite of the fact that this latter test has many weak points.
Acknowledgment The authors wish to thank Regis Raab, who assisted with great skill, and E. I. du Pont de h’emours &- Company, Wlmington, Del., through whose financial help the experiments with the feather manometer have been made possible.
Literature Cited (1) Abel, Bed-Lunge
“Chemisch-Technische Untersuchungsmethoden,” 8th ed., Vol. 3, p. 1287, Berlin, J. Springer, 1933. (2) Berger, Bull. SOC. chim., 11, 1 (1912). (3) Bergmann-Junk, Berl-Lunge “Chemisch-Technische Untersuchungsmethoden,” 8th ed., Vol. 3, p. 1294, Berlin, J. Springer, 1933. (4) Berl, 2. ges. Schiess- U. Sprengstof’w., 4, 81 (1909).
FIGURE 12. EFFECT OF PULPIXG 0.0500 eram of euncotton nitrated with sulfuric-and nit& acids and water. Alcohol-stabilized. 532 mm. air pressure a t room temperature. 135’ C. (uncorrected)
FIGURE 13.
STABILITY
0.0500 gram
532 inin. air pressure a t %50° C. 13.5; C. (uncorrected). Dried 10
looo C. at 1 mm. mercury before entrance of air 1 Kitrated with sulfuric and nitric acids an’d water stabilized with acid and alkali 2. Kitra’ted with sulfuric and nitric acids and water stabilized n i t h alcohol 3. Nitrited with HaPOi, P,Oa, and nitric w i d , stabilized y i t h alcohol 4. Kitrated with acetic and nitric acids, stabilized with slcohol
minutes a t
INDUSTRIAL ,4ND ESGINEERIKG CHEMISTRY
224
(5) Berl and Kunze, Z. angew. Chem., 45, 669 (1932). (6) Berl-Lunge, “Chemisch-Technische Untersuchungsmethoden,” 8th ed., Vol. 5, p. 735, Berlin, J. Springer, 1933. (7) Ibid., Vol. 3, p. 1292. (8) Berthelot-Gaudechon, Compt. rend., 153, 1220 (1911); 154, 201, 514, 1597 (1912). (9) Brame, J. SOC.Chem. I n d . , 31, 159 (1912). (10) Briotet, M e m . poudres, 18, 185 (1921). (11) Duclaux, Bull. soc. chim., 29, 374 (1921). (12) Du Pont, Berl-Lunge “Chemisch-Technische Untersuchungsmethoden,” 8th ed., Vol. 3, p. 1291, Berlin, J. Springer, 1933; 2. ges. Schiess- u. Sprengstofw., 23, 340 (1928). (13) DuprQ,Ann. Rept. Inst. Erplosives, 32, 6 (1907); “Treatise on Service Explosives,” p. 128, London, 1907. (14) Dupr6. Ann. Rept. Inst. Erplosives, 28, 27 (1903). (15) DuprQ,“First Rept. Dept. Comm. on Heat Test as Applied to Explosives,” London, 1914; Marshall, “Explosives,” p. 644, London, J. & A. Churchill, 1917. (16) DuprQAnn. Rept. Inst. Ezploaives, 29, 28 (1904). (17) Egerton, J . SOC.Chem. Znd., 32, 331 (1913). (18) Farmer, J. chem. soc., 117, 1432 (1921). (19) Fric, Compt. rend., 154, 31 (1912). (20) Goujon, M e m . artillerie f r a n p i s e , 8, 837 (1929). (21) Guttmann, 2.angew. Chem., 1897, 265; 1898, 1104; 1900, 592. (22) Hansen, Dansk Artilleri Tids., 12, 129 (1925). (23) Hess, Mitt. A r t . u. Geniew., 10,349 (1879). (24) Ibid., 14, 92 (1883). (25) Ibid.. 10, 360 (1879). (26) Hodgkinson and Coote, Chem. News, 91, 194 (1905). (27) Hoitsema, Z. angew. Chem., 12, 705 (1899); 2. physik. Chem., 27, 573 (1898). (28) Jacqut., Kast-hletz, “Chemische Untersuchung der SprengZiindstoffe,”p. 246, Brunswick, Friedr. Vieweg & Sohn, 1932. (29) Jahresber. Milittirversuchsamt, 3, 20, 69 (1896); 4, 34 (1897). (30) Lenae and Metz, 2. ges. Schiess- u. Sprengstofw., 23, 340 (1928).
VOL. 10, NO. 4
Lenze and Pleus, Ibid., 14, 317 (1919). Metr, Ibid., 21, 186 (1926); 24, 245 (1929). Mittasch, 2.angew. Chem., 16, 929 (1903). Nauckhoff-Philip, “Researches, etc., Ingeniorsvetenskaps Akademien,” Heft 28, Stockholm, 1924. (35) Obermiiller, Mitt. Berl. Bezirksuer, Ver. deutsch. Chem., 1, 30 (31) (32) (33) (34)
(1904).
O’Hern, J. U. S., 40, 148 (1913). Patart, Mem. poudres, 15, 44 (1909/10). Pleus, 2. ges. Schiess- u. Sprengstofw., 5, 121 (1910). Robertson, J. SOC.Chem. Ind., 21, 823 (1902). Robertson and Napper, J . C h a . Soc., 91, 769 (1907). Robertson and Smart, J . SOC.Chem. Ind., 29, 130 (1910). Schaeffer and Treub, 2. physik. Chem., 81, 308 (1913). Silberrad. Ann. Rept. Inst. Erplosioes, 30, 28 (1905). (44)Spica, A t t i Reale Ist. Scienze, p. 27, 1899. (45) Sy, J. Am. Chem. Soc., 25, 549 (1903); 2. angew. Chem., 18,
(36) (37) (38) (39) (40) (41) (42) (43)
940 (1905).
Taliani, Gazz. chim. itd., 51, 1, 184 (1921). Taylor, IND. ENQ.CHEM.,16, 1185 (1924). Thomas, Mitt. A r t . u. Geniew., 15, 203 (1884). Vieille, Monk “La poudre B e t la marine nationale,” p. 134, Paris, 1912; RQglementsde reception des nitrocelldosee et poudres dans les poudreries franpaises. (50) Weeren-Schellbach, Mitt. A r t . u. Geniew., 10, 349 (1879); 14, (46) (47) (48) (49)
92 (1883). (51) Will, J . SOC.Chem. Ind., 21, 819 (1902); Mitt. d. Zcntralst. wiss.- techn. Unters., 2 (1900); 3 (1902); 2. angew. Chem., 14, 743, 774 (1901). (52) Ibid., 45, 669 (1932). (53) Willcox, J. Am. Chem. Soc., 30, 271 (1908). RECEIVED November 1, 1937. Presented before the Microchemioal Section N. C.. April 12 t o 15, 1937. a t the 93rd Meeting of the American Chemical Society, Chapel Hill,
A Procedure for Microfusions CHARLES VAN BRUNT, General Electric Co., Schenectady, N. Y.
D
URISG a recent investigation of a series of transformation products available only in very minute quantities,
using microchemical procedure throughout, insoluble residues of the order of 0.1 mg. in weight were obtained, and it was important to obtain at least a qualitative knowledge of their identity. Scantiness of material required that everything possible be done on a single sample. In such a situation the analyst naturally turns t o a fusion A search of microchemical literature, however, revealed no record of quantitative analytical fusions with such small amounts. Half-milligram charges could not be handled in even the smallest available platinum crucibles without danger of loss, chiefly because of the tendency of the fused material to creep. Electrically heated platinum ribbon is subject to the same difficulty to a high degree. Finally a modified bead procedure proved highly satisfactory. Each residue was obtained in the course of the analysis as a thoroughly washed powder driven into the apex of a microcentrifuge tube. It was withdrawn as a slurry by means of a capillary pipet and deposited upon a platinum ribbon 0.025 x 1.50 mm. which was gently heated by a current. By careful manipulation of the pipet it was easy to concentrate the dried material in about 4 mm. of the ribbon length, all on the upper side. It adhered well enough for the subsequent handling. The end of a piece of 0.508-mm. (0.020-inch) platinum wire was bent into an elongated crook slightly smaller in external dimensions than the section of ribbon carrying the dry residue. This crook was filled Kith the desired amount of flux (KNaC08) by the familiar process of dipping and fusion in the microflame. The section of ribbon was then cut out with scissors and received on the corner of a slide. The flux on the wire was next re-fused
and quickly touched to the deposit on the ribbon section held close t o the flame on its slide. Ribbon and all were thus picked up. Upon reheating, capillary action at once drew the section into a symmetrical position on the crook and held it there, permitting thorough contact of sample and flux during the subsequent fusion, even with a moderate blast. No tendency to creep was observed. Where creeping occurs, however, it can usually be prevented by using a wide flame with its center directed upon the wire shank beyond the fusion so that the heat gradient is always downward t o the fusion.
A decided advantage of this procedure is that the fusion can be dissolved from the wire directly in tubes as small as 2 mm. in bore, thus doing away with the loss or dilution involved in transfer from a crucible. The procedure is not adapted to pyrosulfate: The excess sulfuric anhydride is lost too rapidly and the direct flame causes reduction. Quartz tubes are best for this. With alkaline carbonate a good fusion may be obtained over the direct microburner flame without important contamination from the sulfur content of the gas. RECEIVED November 16, 1937.
Correction An error was made in printing in our February issue the paper by Foulke and Schneider entitled “The Microtechnic of Organic Qualitative Analysis.” In Figure 4, on page 106, tubes A and B should have been shown with open, rather than closed, ends.
