INDUSTRIAL AND ENGINEERING CHEMISTRY
October 15, 1930
371
cible to one side the drop is brought directly over the heating element, which drives off the liquid leaving only the nonvolatile products. This process of solution and evaporation to dryness on the end of a microhook can be repeated on the same spot indefinitely. Chlorides and nitrates of specks too small to be seen with the eye have been formed in this manner with protruding crystal faces sufficiently well developed to exhibit characteristic habits, and by substituting a petrographic microscope for the regular instrument, polarization colors and crystal angles have been measured. With the crystals attached to the tip of a movable tool there is the added advantage that they can be orientated.
given investigation the first step is the separation and isolation of the particle to be studied. Whether the particle be teased out of the material, dissected from it, the material dissolved from around it, or merely selected from among other particles as in a dust, it should be kept in sight after it is once found. The two safe places to leave a particle are (1) in the center of the microscope field, or (2) firmly attached to the tip of a microtool. If the particle is very characteristic in appearance, it may be safely located by coordinates on a slide, but most particles are actually so nondescript that a sufficient number may usually be found on a slide exposed to ordinarily dusty air t o leave a serious doubt as to which is the one under examination.
Conclusion
Solution and Evaporation Methods
Chemical micrurgy, which is chemical work on particles too small for an application of the usual technic, may be utilized in many investigations which are concerned with sources of contamination in the form of very small specks of material. Only general consideration of methods and microtools have been discussed as each individual problem requires its special a d a p tations, and as yet there are no “standard methods.” The present work has merely opened up the possibilities of a new field which should progress with its parent in science, chemical microscopy.
After preliminary tests of the physical characteristics of the particle, such as its hardness, refractive index, electrical conductivity, and its behavior toward heat, its solubility will probably be determined. By means of the micropipet a very small drop of solution is placed on a slide and the particle pushed into it. A different procedure, however, has been used in testing the effect of some of the acids on very small particles. The particle in this case is picked up on a microhook held in one arm of the manipulator. I n the other arm a microcrucible (Figure 2-d) is held with the acid in the cup. With the particle in the fields of the microscope the acid is brought very close under it without actually coming in contact. A gentle heat from the coil around the crucible distils some of the acid solution, which condenses in a minute droplet enveloping both the particle and the hook. This drop does not tend to travel up the shank unless it is allowed to grow altogether too large. By moving the cru-
Literature Cited (1) Chambers, Ana;. Record, 14, No. 1 (1922). (2) Goldstlick, Cham.-Zlg., 48, 629 (1924). (3) Pbterfi, Nalurwisscnsckaftcn, 6, 81 (February, 1923). (4) Taylor, University of California, Publicafhns in Zoblogy, 16, 443. (5) Tech. Assocn. Pulp Paper Ind., Paper Testing Methods, p. 35 (1928). (6) Whitaker, Science, 70, 263 (1930).
Determination of Sulfur in Insecticides and Fungicides b y Carbon Disulfide Extraction’ Richard Edge FOOD,DRUG,A N D
rNSBCTICIDB
ADMINISTRATION, u.
s.
DEPARTMEST OF
AGRICULTURE,
wASHINDTON.
D.
c.
Samples of insecticidal aud fungicidal dusts freULFUR is frequently Preliminary Experiments quently contain sulfur as flowers of sulfur, much of determined in insectiwhich sulfur may be insoluble in carbon disulfide. At first it was thought posc i d a l a n d fungicidal A method has been developed whereby all the free sible to convert the flowers dusts by extracting with carsulfur is converted, with practically no loss, to the into soluble sulfur by treating bon disulfide and weighing carbon disulfide soluble form through the agency of with various volatile reagents method the extracted sulfur. controlled heating, in which form it may readily be This is r a p i d and easily that could later be removed determined by carbon disulfide extraction. carried out, but the results by evaporating to dryness are often inaccurate owing to on a s t e a m bath, but no the presence of forms of sulfur insoluble in carbon disul- success was obtained by this method. A quantity’ of sulfur fide. In such cases it is necessary to use an oxidation insoluble in carbon disulfide always remained. The use method and determine the sulfur by precipitating and of heat for the conversion was then tried. Several samweighing as barium sulfate. This paper describes work which ples of flowers of sulfur were heated overnight in an oven has led to a modification of the carbon disulfide method by regulated a t 103’ C., and were then found to be completely which it is made applicable to such dusts. The method of soluble in carbon disulfide. With this knowledge of the attacking the problem is based on the fact that heat causes a manner in which flowers of sulfur could be made soluble, the change in the physical properties of the different forms of sul- next problem was to determine the applicability of this fact fur. to the quantitative determination. Flowers of sulfur for this work, purchased on the market, The first attempt was to heat the sample containing the were found to be soluble in carbon disulfide to the extent of sulfur, mixed with various other materials that are the usual 68.83 per cent. By oxidation with bromine and nitric acid, constituents of insecticides and fungicides, in the oven a t a and calculating the sulfur in the barium sulfate obtained from definite temperature and for a given period of time. This the barium chloride precipitation, results varying from 99.60 procedure gave results that were fairly constant, except in the to 99.75 per cent sulfur were obtained. presence of moisture or lead salts. In order to make the method more widely applicable and 1 Received April 29, 1930.
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372
ANALYTICAL EDITIOiY
less influenced by existing conditions, the various ingredients comprising the insecticidal and fungicidal dusts were dissolved from the sulfur before it was heated in the oven. Strong hydrochloric acid was a satisfactory solvent except in the presence of lead salts, in which case, even though well washed, considerable lead chloride remained upon the filter. The residue of lead chloride reacted sufficiently with the sulfur when placed in the oven to cause an appreciable blackening on the filter, indicating the formation of lead sulfide, and variable results were obtained. Nitric acid was then substituted for the hydrochloric acid and proved satisfactory in all cases except those in which a considerable quantity of both lead salts and sulfates were present in the sample. Since this combination is seldom encountered in the insecticides and fungicides containing sulfur, the method has been developed using nitric acid as the solvent. A dilution of 1 to 2 was finally chosen as the most satisfactory strength, as the cold acid a t this dilution has a negligible oxidizing effect on the sulfur. Five grams of flowers of sulfur were treated with the quantity and strength of nitric acid recommended in this procedure and the filtrate yielded by the oxidation method 0.0928 gram of barium sulfate, which represents 0.04 per cent sulfur. To insure thorough penetration of the sample by the acid it was first wetted with dilute alcohol (1 part 95 per cent alcohol to 3 parts water). The solubility of sulfur iq alcohol of this dilution is also negligible. After wetting with alcohol, nitric acid (1 : 4) was added to prevent a too rapid reaction with the constituents, particularly carbonates, that might be present in commercial samples.
oxidation method which is often used on samples of this type. The results for column 3 are not quite so good, and indicate that a small quantity of sulfur was lost in the procedure. This loss was probably due to inability to extract all of the sulfur rather than to a reaction between the residue and the sulfur. Tests made on these residues after leaching gave no indication of sulfides. If such samples were analyzed by the method of bromine and nitric acid oxidation, considerable difficulty would be encountered and, unless great care were taken, the results would probably be no better than those obtained by the method described. T a b l e I-Recovery
Results
This method was tested on samples of the approximate composition of commercial products and the experimental results are given in Table I . The results in column 2 , for samples in which the ingredients other than sulfur a r e soluble in acid, compare very favorably with those obtained by the tedious and lengthy
of S u l f u r from Mixtures C o n t a i n i n g Flowers of Sulfur 1 gram; lead arsenate, 2 grams; calcium hydroxide,
MixtFre 1-Sulfur, z grams Mixture 2--Sulfur, 1 gram; lead arsenate 2 grams' calcium sulfate 2 grams Mixture 3-Sulfur, 1 gram; lead arsenate, 2 grams; calcium hydroxide, 2 grams; copper sulfate, 2 grams; sodium silicofluoride, 2 grams Mixture .i-Sulfur, 1 gram; calcium hydroxide, 2 grams: heated without acid extraction
TEMP. OF
HEATING RESIDUES MIXTURE1
c.
Prr cent
MIXTURE2
MIXTURE3
MIXTURE4
P n cent
Per cent
Per cent
TIME OF EEATXNQ, 4'/n HOURS
105
10:
110
Procedure for Proposed Method
Weigh into a small beaker, preferably of about 150 cc. capacity, such a quantity of sample that the sulfur content will fall between the limits of 1 and 3 grams. Moisten the sample with 10 to 15 cc. of alcohol (1:3), then add slowly about 15 cc. of nitric acid (1:4),and stir. When the violence of the reaction has ceased, add about 40 cc. of nitric acid (1:2), then stir well, and allow to stand without heating for about 5 minutes. Decant the liquid through filter paper in short-stem funnels. Then add 10 to 20 cc. more of the nitric acid (1 :2) in order to dissolve any acid-soluble material remaining from the previous acid treatment. Filter, wash a t least three times with water, then allow the residues to drain 20 or 30 minutes or else overnight. If the residues drain 20 to 30 minutes, heat for 41/r hours, if overnight 4 hours, in an oven regulated a t 105-110" C., preferably about 107" C. The shelf holding the filters should not be more than 2 or 3 cm. below the bulb of the oven thermometer, preferably less. After the sulfur has been heated for the length of time recommended, remove the funnels holding the filters and extract the sulfur with successive small quantities of carbon disulfide until 50 cc., or more, if it should appear necessary, have been used. Receive the carbon disulfide solution in tared beakers. Place the tared beakers containing the solution on a steam bath and evaporate off the carbon disulfide. Allow the beakers containing the sulfur to remain on the bath about an hour after the carbon disulfide has evaporated, then wipe off any moisture that may be present, place in a desiccator for several hours, preferably overnight, and then weigh.
Vol. 2, No. 4
99.68 99.60 99.52 99.54 99.47 99.32 99.85 99.60 99.42 99.07 99.70 99.71 99.68 99.63 99.54 99.53 99.52 99.40
99.04 88.90 98.52 98.42 97.84 97.23 99.75 99.63 99.16 99.13 99.11 99.87 99.65 99.92 98.85 99.07 98.68 98.65 99.08
99.45
99.33 99.26
98.73 98.63 98.40
TIME OF HEATING. 1 HOURS: RESIDUES DRAINED OVBPNIGHT
105
99.53 99.12" 99.18 97.84 99.72" 98.79 99.56 98.51" 99.51 97.89 99.77" 110 99.24 99.55" 99.52 99.24 99.71" 98.01 99.69" 99.17a 99.710 99.395 99.72" 99.23" a Samples Containing 2 grams sulfur.
I n the work reported in Table I there was a considerable drop in the temperature of the oven when the samples were put in, and in some instances about an hour was required to regain the temperature a t which it was set, but no allowance was made for this in the time of heating. Slight variations of both time and temperature are permissible, as results obtained from slightly shorter and longer periods of heating at 105" and 110" C. showed but little variation from those reported in the table. An advantage of the overnight drainage and the 4-hour period of heating is that less time is required in the same day to complete the analysis, and therefore may prove of greater convenience to the analyst. It Tyas hoped that the period of heating might be lowered still further, but a 3-hour period a t 105' C. was found insufficient to convert all the sulfur to carbon disulfide-soluble sulfur. Effect of Longer Heating Period
Experiments were also carried out t o determine the effect of a longer period of heating, and also the effect of different temperatures on the transformation of the sulfur. In these: experiments the residues were heated in the oven overnight (17 to 18 hours). The results are given in Table 11.
TNDUSTRIAL AND ENGINEERING CHEMISTRY
October 15, 1930 Table 11-Recovery
of Sulfur f r o m Mixtures C o n t a i n i n g Flowers of S u l f u r after Heating Overnight Mixture 1-Sulfur, 1 gram; calcium hydroxide, 2 grams; lead arsenate, 2 grams Mixture 2-Sulfur, 1 gram; calcium sulfate, 2 grams: lead arsenate, 2 grams TEYP. OF TEMP. OF HEATINO HEATINO RESIDUE MIXTURE 1 MIXTURE 2 RESIDUE MIXTURE 1 1MIXTURB 2 a C. Per crnt Per rent O C. Per ccnf Per cent 95 98.82 97.60 102 99.41 98.82 98.73 99.02 99.26 98.20 98.64 99,36 98.92 97.83 97.6 99.07 97.97 99.25 98.88 99.32 98.20 99.15 98.60 97,76 99
101
99.08 99.66 99.20 99.58 99.97 98.42 99.16 99.49 99.14
105
99.55 98.97 98.90
99.03 98.69 98.64
106.5
99.10 98.14 97.02
99.32 98.67 99.10
98.92 98.20
From this table it is evident that a fairly reliable determination could be carried out by filtering and placing the samples in the oven overnight, at a temperature ranging between 98" and 102" C. Blanks run on the carbon disulfide to determine the amount of non-volatile material gave residues of about 0.0007 gram per 50 cc., so that the error from this source was slight. The percentage of recovery of sulfur should be slightly increased by the use of samples larger than 1 gram, as indicated by the results in Table I from the samples which con-
373
tained 2 grams. This is probably due to a dependence of the rate of volatilization on the actual surface exposed. Loss of Sulfur during Heating
The loss in weight of sulfur from heating is shown in Table 111. TableJII-Loss of Weight of Flowers of Sulfur i n Uncovered Weighing Bottles Temperature, 110' C., time of heating, 41/1 hours WEIGHT OF SULFUR SULFUR LOST Grams Gram Per ccnl 1 0.0028 0.28 1 0.0033 0.33 1 0.0020 0.20 3 0,0089 0.30 3 0.0041 0.14 3 0.0026 0.09 5 0.0044 0.09 5 0.0063 0.13
The sulfur in the bottles a t the above temperature showed signs of partial melting. The variable results are probably due to differences in the surfaces of the sulfur exposed to volatilization in the different sized weighing bottles. Conclusion
This method has been worked out primarily for the sulfur determination in samples of insecticidal.and fungicidal dusts, but should prove satisfactory for any sample in which the ingredients, with the exception of sulfur and siliceous material, are acid-soluble.
Color in the Sugar Industry' 111-Preparation of Asbestos for Use as a Filter Aid J . F. Brewster and F. P. Phelps B U R E AOF ~ STASDARDS. NASHINGTOK;. D. C .
I
T HAS been shown in a previous publication ( 2 ) that purified asbestos is a suitable medium for the clarification and filtration of turbid sugar solutions for colorimetric analysis in that it causes little or no modification of the coloring matter by chemical action and no undue loss thereof by adsorption. At the same time, owing to its fibrous structure, asbestos permits a reasonably rapid filtration of sugar sirups of high density and viscosity. Crude asbestos contains colloidal impurities and extremely fine fibers that must be remor-ed. The presence of iron oxide is objectionable for it may cause a qualitative change of color in sugar solutions, as frequently happens when untreated materials are used. Heretofore the asbestos has been subjected to acid treatment followed by a tedious washing process that required several days. Munson and Walker ( 1 ) have described a chemical treatment for the purification of asbestos to be used in the filtration of cuprous oxide in their method of determining reducing sugars. This consists of alternate digestion with acids and alkali whose concentration is not in every case stated, and the process extends over several days. The treatment described below may be completed in about 2 hours. Colloidal impurities along with iron oxide are removed by decomposition and solution as well as the extremely fine fiber. The coarser fiber appears to be very little affected. At the time of forming the filter pads, some washing is necessary to remove fine fiber broken off by abrasion. This washing is quickly accomplished. Received July 25, 1930. Preliminary report presented before the Division of Sugar Chemistry at the 77th Meeting of the .\merican Chemical Society, Columbus, Ohio, April 29 to XIay 3, 1929
Method
To 25 grams of asbestos are added 250 cc. of sodium hydroxide solution, sp. gr. 1.284 a t 20"/4" C. This is about a 25 per cent solution and technical sodium hydroxide may be employed. The mixture is boiled 30 minutes, no attempt being made to prevent evaporation. A clean nickel or iron vessel such as a sand bath may be used for this digestion, but a Pyrex round flask is suitable. I n the preliminary experiments a 45 per cent alkali solution was permitted to boil down in the flask. The glass was severely attacked, but the long asbestos fiber withstood the action of the alkali. A fusion with alkali is, of course, to be avoided. After digestion the mixture is filtered hot by suction and washed repeatedly with hot water. The asbestos, which has been pressed in the funnel to force out most of the water, is transferred to a flask and treated with 250 cc. of hydrochloric acid, sp. gr. 1.20, and 25 cc. of nitric acid, sp. gr. 1.42. The mixture is shaken so that the pulp is disintegrated and then heated 30 minutes on the water bath. At the end of this period 250 cc. of hot water are mixed with the contents of the flask and the asbestos is filtered by suction as before and n-ashed repeatedly with hot distilled water until all acid is removed. The purified asbestos is to be protected from dust. It is dried in an oven at 110" C. and stored in a clean glass container. Literature Cited
1
(1) Slunson and Walker, J . A m . Chem. Soc., 28, 666 (1906). ( 2 ) Peters and Phelps, Bur. Standards, Tech. Paper 338, Pt. I1 (19271.
