JANUARY 15, 1938
ANALYTICAL EDITION
shaped particles rejected. A microscopical determination of the size-distribution curve of a fine abrasive powder requires no more skill and care in manipulation than does a determination of equal accuracy by the sedimentation method. Size numbers obtained b y the two methods are in close agreement for symmetrically shaped abrasives. For abrasive flours coarser than those shown in Figures 1
47
and 2 the sedimentation tube method is relatively rapid and easy to carry out.
Literature Cited (1)
Work, L. T.,Proc. Am. Soc. Testin0 ;Materiels, 28, 771 (1928).
RECKIVED
June 4, 1937.
Microchemical Analysis of Colored Specks and Crystalline Occlusions in Soap Bars HERBERT K. ALBER1 AND CLEMENT J. RODDEN2 Washington Square College, 4 e w York University, New York, N . Y.
T
HE emphasis in the microchemical literature is usually
placed on the description of new methods or on the development of special apparatus. The practical application of these methods to the solution of analytical problems which cannot be solved by the usual methods is seldom mentioned, except in the analysis of valuable objects of art, etc. The present paper describes two cases which illustrate the practical value of the so-called “classical” micromethods. Considerable time and effort spent in the application of ordinary methods of analysis to these two problems failed to yield a solution. Since the difficulties entailed the loss of a large amount of merchandise, a discovery of the cause was of considerable importance to the manufacturer. Rlicromethods of analysis were therefore used and in a comparatively short time yielded the necessary data for locating the source and preventing a further recurrence of the trouble. T h e final solution may seem surprisingly simple. I n the following discussion, only deviations from known microprocedures are described in detail.
the elements, which will be described in a future publication. The analysis showed the following results: carbon, ; hydrogen, +; halogen, -; nitrogen, -;,phosphorus, -; sulfur, (the strength in each test is indicated by over 25 per 10 t o 25 per cent; 1 to 10 per cent; -, negative cent; reaction). Emich’s sulfur test consists in oxidizing the sulfur of the organic compound to sulfate by heating with nitric acid in a sealed capillary; since the temperature should not exceed 300’ C., the test can be carried out just as accurately in less expensive Pyrex glass capillaries of about 1-mm. wall thickness and 1- to 2-mm. bore, with the usual precautions. B y comparing the length of the barium sulfate column with those produced from known amounts of sulfur-containing materials, an estimation of the sulfur content within the given limits is easily made. The supernatant liquid is transferred to another capillary and the phosphate is precipitated and estimated as ammonium phosphomolybdate by comparison with k n o m amounts of phosphoruscontaining substances.
++,
+,
++ +++,
++
Qualitative Microchemical Analysis of Colored Specks in Soap Bars SAMPLE.Colored specks were distributed on and in a single soap bar, from which they were isolated by cutting the soap in such a way that at least one surface of the particle was exposed. Under the binocular microscope the specks were lifted off with fine needles and collected on a microculture slide with a small concavity. About 35 such specks, a few of them pure soap only, were submitted for microanalysis. Investigation under the microscope showed several types of particles which are illustrated in Figure 1. With the microchemical manipulator designed by one of the authors (1) all b, d, and e particles were separated, and then the major part of the adherent white material was removed under the binocular microscope (magnification, X 30). I n order to obtain preliminary information on the ingredients and technic best suited to the problem, the white particles were analyzed first. ANALYSIS OF W H r T E
PARTICLES. About 15 white particles,
a, and separated white portions d and e collected in a platinum dish 10 mm. in diameter, weighed 48 micrograms. With 20
micrograms of this sample a qualitative organic elementary analysis was carried out, using Emich’s procedures (6, f f ) and some modifications by Alber for estimating the percentages of 1 Present address, Biochemical Research Foundation of the Franblin Institute. Philadelphia, P a . 2 Pie-eut address, National Bureau of Standards, Washington, D. C ,
(x
FIGURE 1. COLORED SPECKS ISOLATED FROM S O A P 20) Taken with a Reichert photomicrographic apparatus i n reflected light u . Pure n h i t e particles n-ithout any special structure b. Reddish brown a n d dark-brown particles, uniformly colored throughout c . Yery slightly yellow particles d. White particles with very small dark spots, which appear black. sometimes dark green i n reflected light. T h e dark specks have distinct boundaries, hut are apparently isotropic in polarized light e . Different combinations, of t h e above types. such as white or yellow uarticles u i t h brownish Dortions. the color of which shades off gradually
VOL. 10, NO. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
48
The remaining 28 micrograms of white particles were carefully ashed on a metal block, leaving a white residue weighing approximately 4 micrograms (observation in reflected light under the microscope). The solution of this residue in N hydrochloric acid was used for the following tests: sodium test with magnesium uranyl acetate, sulfate test with barium nitrate, flame test (hand spectroscope), sodium present alone. Tests for groups 1, 2, and 3 with Emich’s fiber technic (1, 3, 5 , 6) gave negative results. This “group indicator method” has been successfully used throughout the investigation. Since the precipitates on the fiber ends can be redissolved, even the smallest amounts are not sacrificed.
++;
++;
of the constituents within 5 per cent (relative). The microtechnic of working in centrifuge cones, as described above, introduces the possibility of a less accurate estimation through losses by adsorption on the comparatively large wall surfaces, since the total weight of the elements present is so small. I n the final steps of the identification and comparison with known amounts, smaller vessels with less surface were utilized, and corresponding reductions in the amounts of the reagents were made. Fine capillaries of 0.5-mm. bore allowed a differentiation in the lower region of concentrations between 5, 3, 1, 0.5, and 0.1 micrograms, and permitted their comparison with known quantities of the same element. Confirmatory tests on the isolated precipitates were carried out by means of color reactions with Feigl’s drop-test technic (1, 7). If the absence of certain elements was obvious, the procedure for these groups was shortened-e. g., in the arsenic group no yellow or orange sulfide precipitate could be noticed, thus eliminating the specific tests for arsenic and antimony. The only unexpected difficulty in the course of the analysis was the appearance of platinum, which, at the time of the experimental work, was not included in the original scheme. Benedetti-Pichler (2) has described a finer microtechnic for 1microgram solid samples and 0.01-cu. mm. reagent portions, which must be measured and handled with the use of Chamber’s micromanipulator. A special analysis of one single brown speck (b, Figure 1) showed the presence of more soap (carbon, sodium, sulfate, f;chromium, -; iron, ++) than in the black particles, as well as the absence of chromium. This one particle was ashed on a quartz slide t o prevent the disturbing influence of platinum. The same precaution was used in the sshing of a test sample of similar composition, as revealed by the analysis of the main portion of the colored specks. Such analysis of a known mixture seemed necessary in order t o prove that it was permissible to make comparison tests for the estimation of such small quantities. To some extent, it also showed the precision of the modified microtechnic, although many more such test analyses would have been necessary.
++;
++;
FIGURE 2. DESDRITICCRYSTALLINE SOAPBARS( X 7)
OCCLUSIONS IN
Photomicrograph in reflected light with a green filter
It was concluded that the white particles were pure soap with sodium sulfate as an inorganic constituent. About 20 colored ANALYSISOF BROWX AND BLACK PARTICLES.
specks (b, c, and separated dark spots d and e, but not including the one brown particle, b, shown in Figure 1) weighed 59 micrograms. When the sample was carefully treated with nitric acid and sulfuric acid in a platinum dish on the water bath, a slight reaction on the black particles was noticed. Complete ashing a t about 600” C. gave a residue of 32 micrograms, which formed colored zones, a dark-red inner, bright-red center, and w k t e outer ring (oxides, sulfates). The water-soluble part was extracted with 0.5 ml. of distilled water; the extract gave a positive sodium test and a positive sulfate test, so that most of the white residue consisted of sodium sulfate. The remaining material was only partially soluble in nitric acid (I to 1). Treatment with hydrochloric acid (1 to 1) dissolved all except a few colored spots, which were brought into solution by fusing with sodium borate and dissolving this borax bead in diluted hydrochloric acid (1 t o 10). The platinum dish lost about 20 micrograms during these manipulations; the platinum was detected in the analytical procedure to the extent of more than 10 micrograms (Table I). All the solutions were combined in a 1-ml. centrifuge cone, evaporated to dryness, and dissolved a ain in 0.2 M hydrochloric acid; since no residue remained, the a%sence of group 1 was established. About 1 cu. mm.-i. e., one-tenth of the acid solution-was evaporated on the end of a cotton fiber. The substance, collected on the fiber tip, was exposed to ammonium sulfide by drawing the fiber through the reagent droplet three or four times, forming a black precipitate (all observations on the fibers were made under the microscope in transmitted and reflected light with various colored backgrounds, 1 ) . One cubic millimeter of hydrochloric acid partially dissolved the sulfides, indicating the presence of groups 2 and 3. The remaining precipitate on the fiber end was treated with a droplet of aqua regia, and both solutions were combined with the original sample. The resulting acid solution was analyzed according to a modification of the qualitative microscheme of BenedettiPichler and Spikes (S), which allows a quantitative estimation
Table I indicates the results of analyzing the main portion
of the colored specks, the confirmatory tests for the different elements, and the results of the test analysis.
Elements Found in Tested for Main Sample
Confirmatory Tests (7)
PB.
PQ.
Na Group 1 Sn Pt” Ph cu Bib Co
f
-
1-0.5 More than 10
0.5
-
Results of Test Analysis Present Found
Suectroscoue
Flame test Dithizone -
Fiber test (0) Rubeanic acid
3
-2 1 -
-
PQ.
-1 -
More t h a n 1
1-0.5
-
1
0.5-0.1 1
Diphenylcarbazide
20 1 1
-
-
More t h a n I5 3 1
-
a,a’-dipyridyl
Morin ( 6 ) Spectroscope
-
-
2 Ca,= 3 Stearic acid = 10 34
-
1
5
++
About 31 Total About 20 N, P, halogen = negative. a Not present in original sample: introduced from platinum vessel (loss = 20 Pg.1 b Pro’bahly introduced by an impure reagent, as seen from the test analysis. C Not tested for, since solution was lost by an accident; n o indication of the presence of these two elements i n any step of the analysis.
It was concluded that the brown specks, b and probably also c, consisted mainly of soap colored with iron. The black specks contained very little soap; the main constituent was iron with 5 to 10 per cent of chromium, 5 per cent of cobalt, 1 to 5 per cent of lead and tin, and small amounts of sodium sulfate from adherent soap, The source of these contaminations in the soap bars could be traced b y the analytical results,
JANUARY 1.5, 1938
ANALITIC.4L EDITION
49
and further disturbances during the process of manufacturing eliminated.
Microchemical Analysis of Crystalline Occlusions i n Soap Bars QUALITATIVE. The crystalline occlusions were dendritic in form, as shown in Figure 2, and appeared in a surface layer approximately 1 mm. thick on the soap bars; these crystals appear to be the result of efflorescence. T h e sampling of these very tiny crystals was difficult because of their enclosure in the soap. Since no special mechanical device was applied for the sampling, it took about 6 hours to collect the material necessary for a preliminary qualitative analysis. Crystal aggregates from several bars of soap were lifted out with a spear-shaped dissecting needle. I n the same way samples of soap without crystals were taken from the surrounding areas, Analytical Procedure. Both samples were ashed with sulfuric acid in platinum macrocrucibles. As the residue determinations indicated that some inorganic material constituted the major portion of the crystals, i t was decided to run a qualitative analysis on the ash, in both cases using the unmodified analytical scheme of Benedetti-Pichler and Spikes (3). The results of these analyses are shown in Table 11. The composition of pure soap from bars containing crystals and from bars without any crystals was found to be identical, as established by a special set of analyses. The method of sampling, however, did not warrant drawing accurate conclusions from the qualitative analysis. The authors n-ish to thank IFr, F. Spikes for performing the major portion of the qualitative analysis (1935). TABLE 11. QUALITATIVE ANALYSIS Crystals Contaminated with Soap
denum, chromium
Soap without Crystals
denum, chromium
QUANTITATIVE.At this point i t was decided to obtain some of the crystals in as pure a state as possible and to perform a quantitative microchemical analysis of the constituents. The type of analytical work required could not be anticipated, but had to be chosen while going through the different steps of the procedure. The crystals for these determinations were all taken from the surface of soap bars, where, during efflorescence, the soap film covering the crystals had ruptured. A binocular microscope (magnification, X 30) served to control the isolation and removal of the crystalline occlusions with a dissecting needle. About 140 bars of soap were used in order to collect 1.376 mg. of these crystals, as free as possible from soap; this procedure required about 60 hours. The results of the qualitative analysis (Table 11) led primarily to the conclusion that tin soap was present in the crystals. Because of the insolubility of tin soap in cold water, a moisture determination (volatile matter a t 105' C.), a n analysis of the water-soluble products, and a carbon and hydrogen determination, as well as a tin determination in the water-insoluble material, seemed necessary to confirm this opinion. As, with such a small sample, too frequent changes of the reaction vessels were undesirable, a special platinum boat was prepared b y piercing the bottom of a n ordinary platinum microboat for carbon and hydrogen determinations (8) 27 times with a fine needle. A platinum-sponge filtering layer about 0.75 mm. thick was superimposed on this perforated
i
bottom in the usual m a n n e r , as in the p r e p a r a t i o n of D o n a u d i s h e s (4). The capacity of the boat is about 0.15 to 0.20 ml. (Figure 3 4 shows such a filter boat, which is obt a i n a b l e from the American Platinum Works, Kewark,
N. $J.)
3
Some advantages of this filter vessel are the f o l l o w i n g : 2 The sample can be treated with various solvents, cold or hot Icm acids, etc.; the platinum-sponge 1a y e r retains barium sulfate p r e c i p i t a t e s FIGURE3. FILTERING DEVICE FOR quantitatively; beUSE WITH MICROPLATINUM FILTER cause of thestandard BOAT dimensions (12 x '5 X 4 mm. high) disk it can be used in the s t a n d a r d combustion tubes; all the G . Cotton advantages of platinum, such as constant weight, quick cooling, etc., remain; capillary attraction reduces the tendency of small volumes of liquids to creep over the walls. By means of the filter boat, micropreparative work can be combined directly with quantitative determinations without any change of the vessel-e. g., recrystallizations and isolation of small amounts of crystals, drying, extracting impurities, treatment under varying conditions such as exposure to certain vapors-and finally, the microchemical quantitative analyses can be carried out in one filter boat. For the filtration, the filter boat is placed on the frittedglass part of Donau's suction apparatus (4) or on the glass filter stick (No. 91 G 3 of Schott and Genossen, Jena) which has the permanently fused-in fritted-glass filter disk shown in Figure 3B.
I. Determination of Moisture (volatile matter at 105" (3.). The air-dried crystals were weighed in the filter boat and heated in a Pregl drying block ( 8 ) at 105" C. for 20 minutes to constant weight. All the weighings were carried out with the utmost care under continuous control of the zero readings and the sensitivity of the Kuhlmann microchemical balance. Changes in temperature and moisture content of the balance room were observed and influences of changes in the barometric pressure were eliminated through tares of the same density and similar shape. These precautions were essential for success in working with a 1.3-mg. sample. 11. Analysis of Water-Insoluble Matter. The boat with the dry sample was placed on the filtering device (Figure 3) and treated with 2 ml. of cold water in small portions, allowing each portion t o stand in contact with the particles at least 30 seconds before applying suction. The solution was collected in a lass microbeaker. The water-insoluble residue was then drie! in the filter boat to constant weight under the same conditions as above.
The small quantity of insoluble material prevented a carbon and hydrogen determination as originally planned; a qualitative analysis was performed instead. A few drops of hot, concen-
trated sulfuric acid partly dissolved the residue, the filtrate being collected in a 5-ml. platinum crucible. Since it was impossible to tell by visual observation whether complete solution had taken place, the boat was heated on a metal block t o drive off the excess of sulfuric acid, and weighed again. I t was found that
INDUSTRIAL ASD ENGINEERIKG CHEMISTRY
50
not all of the residue had dissolved. The remainder was treated with concentrated hydrochloric acid, which finally caused complete solution. The combined acid extracts were concentrated by blowing air on the surface of the heated liquid. The liquid became brown during this treatment, indicating the presence of organic material. After evaporation to dryness, the residue Fats dissolved in a few drops of dilute hydrochloric acid (1 to 5 ) , and tested by bubbling hydrogen sulfide through the solution from a fine capillary. A positive test for tin mas obtained, but no quantitative determination was performed. S o other elements of groups 2, 3, or 4 were detected. The conclusion drawn from these experiments was that the major portion of the water-insoluble material in the crystalline occlusions was tin soap.
111. Analysis of Water-Soluble Matter. The amount of water-soluble material was calculated from the insoluble matter by difference. The water extract was transferred with a fine capillary pipet from the glass microbeaker into a platinum microboat, in which it was evaporated and dried at 110” C. A small amount of material was lost in this procedure, 0.228 mg., as calculated from the difference in t’he weighings. For the final calculations it was assumed that the lost portion contained the elements in the same proportions as those found in the analysis. (a) A carbon and hydrogen microdetermination was carried out on the dried sample in the usual manner, but the results had to be corrected because of the noticeable blank tests obtained during the hot summer months as a result of the high humidity and the extremely small amount of sample (organic matter only 0.228 mg.). Comparatively reliable results could be obtained only if “block analyses”-i. e., analyses with about 1.300 mg. of salicylic acid before and after burning the actual sampleestablished exact corrections for the water and carbon dioxide. The residue consisted of sodium sulfate and sodium chloride, as ahown by the good agreement of the total weight (0.795 mg.), as calculated from the chloride and sulfate data, with the actual residue (0.796 mg.). (b) The residue in the platinum boat was completely soluble in distilled water. To determine chloride, the solution was introduced into a weighed glass microbeaker for the filter-stick metbod of Emich ( 6 ) , and the chloride determined by precipitatior, with silver nitrate. ( c ) To determine sulfate, the filtrate from the chloride determination was collected quantitatively in a glass microbeaker, the excess of silver was precipitated with hydrochloric acid, and the silver chloride was filtered off and washed three times with hydrochloric acid (1 to 100). The clear filtrate and the washings were collected in a porcelain crucible with a black glazed inner surface, a type now in general use for barium or sulfate determinations, together with the porcelain filter stick of Emich and Schwarz-Bergkampf (6, 9, IO). The solution had at this point a volume of about 10 ml.; a small portion of it was treated with hydrogen sulfide without noticeable precipitation, and a side test in another drop for group 3 gave negative results. The treated portions ryere heated on a water bath to remove hydrogen sulfide, combined with the major part of the solution, and the sulfate determination was carried out by precipitating with barium chloride crystals. ( d ) , To determine sodium, the filtrate from the sulfate determination was collected in a glass beaker and the excess of barium
VOL. 10, NO. 1
removed mith sulfuric acid (1 to 5 ) . After filtering off the barium sulfate by means of a porcelain filter stick, the solution was evaporated in a platinum microboat on a water bath, and the sodium determined as sodium sulfate in Pregl’s micromuffle (8). The sodium sulfate dissolved completely in water, and the solution gave no tests for group 4 or other elements of group 5 . From the results reported in Table 111,the complete analysis (Table IV) could be calculated. For the calculation it was necessary to assume that the water-insoluble material was pure tin soap. TABLEIv. CALCUL.4TED Determination Lfoisture Tin - - -R~-O-R-~D_ Organic matter (sodium soap and free i a t t y acids) Sodium chloride Sodium sulfate Total
Per Cent Found
pi 20 3 2.0 68 i 100, oa
ANALYSIS
Calculated from: Volatile matter, I Water-insoluble matter, I1 Carbon and hydrogen, loss of aeight on burning, I11 a (organic part of tin soap not included) Chloride determination, 111 b Sulfate determination. 111 c
~
a The 100.0% yield should not be considered as a n indication of such high accuracy.
Conclusion
The main constituent of the crystalline occlusions in the soap bars was determined to be sodium sulfate. Because of the small moisture content the sodium sulfate was almost dehydrated. The tin soap was present in a higher concentration than in the soap without crystals and may be tied u p with the formation of the crystals. The chloride content was comparatively small. The sodium soap was calculated from the organic matter in the water-soluble part of the crystals and was not considered as a constituent of the crystals, Quantitative mechanical separation of the dendritic crystals from the soap was nearly impossible. Summary The application of microchemical methods in industrial problems is illustrated by the analysis of heterogeneous particles in soap bars. I n the two cases described, the use of microtechnic enabled explanations to be given for the appearance of troublesome disturbances during the process of manufacturing soap; attempts to apply macrotechnic to these problems had failed. The use of “classical micromethods” is emphasized; modificitions were made only when the extremely small amounts of material a t hand demanded them. A new microplatinum filter boat is described which permitted seven successful quantitative determinations to be carried out on a single sample weighing 1.3 mg.
Literature Cited TABLE
No.
111. QUASTITATIVE ANALYSIS
Type of Determination
I
Volatile matter a t
I1
Water-insoluble matter Qualitative analysis of I1
1050
I1 a 111
c.
Water-soluble matter 111 a b Carbon Hydrogen Residue in 111 111 b Chloride in residue from I11 a 111 c Suliete in residue from I11 a I11 d Sodium in residue from I11 a 0
b
Weight of Reaction Products Sample Determined as M g .MB. 1.376 Loss in weight 0.048
.
Found
% 3.5
1.328 Residue insol. 0.076 6.7 in water 5 50 0.076 Organic material and tin, probably in form of tin soap. Groups 2, 3, and 1 , 3 2 8 Water extract, oalcd. from I1 COZ 1.024 Hz0 1,024 Residue 1.024 BgCl 0,796
1.252 0.575 0.2i5
0,796 0.055
0,796
Bas04
1.27
0.796
SanSOa
0.881
94.3 91.0” 15.3 3.0 7 7 . 7 (70.7a) 1.7 (1.24)
65.7 (46.40) 35,s (25.39
Values calculated on basis of air-dry sample (original crystals). Refers t o the previous remark concerning loss of material (0.228 mg.).
Alber, H. K., Xiiarochemie, 14, 219-4-1 (1933/34). Benedetti-Pichler, A. A , , IXD.ESQ. CHEsf., Anal. E d . , 9, 483-7 (1937). Benedetti-Pichler, A. A., and Spikes, IT. F., “Introduction to the Microtechnique of Inorganic Qualitative Analysis,” Douglaston, N. Y., Microchemical Service, 1935. Donau, J., Xonatsh., 60, 129-40 (1932). Emich, F., “Lehrbuch der Nikrochemie,” 2nd ed.. Munich, J. F. Bergmann, 1926. Emich, F., and Schneider, F., “hficrochemical Laboratory hfanual,” Xew York, John Wiley &. Sons, 1932. Feigl, F., “Qualitative Analyse mit Hilfe von Tupfelreaktionen,” 2nd ed., Leipzig, Akademische Verlagsgesellschaft, 1935. Pregl, F., “Quantitative Organic Microanalysis,” edited by H. Roth, tr. by E. B. Daw, 3rd English ed., Philadelphia, P. Blakiston’s Son and Co., 1936. Saschek, W., ISD. ESG. CHEM.,Anal. Ed., 9, 491-2 (1937). Schwars-Bergkampf, E., 2. anal. Chem.. 69, 321 (1926). RncnImD September 1, 1937. Presented before the Microchemical Section a t the 94th Meeting of t h e American Chemical Society, Rochester, N. Y., September 6 t o 10, 1937.
