Ashing Plant Materials to Determine Total Phosphorus B. W. HOWKWITH E. E. DETURK,University of Illinois, Urbana, Ill. METHOD has been worked out1 which offers some advantages over the somewhat tedious and timeconsuming standard magnesium nitrate method for oxidizing plant samples for total phosphorus determination. It consists essentially of mixing the weighed sample with an excess of pure calcium carbonate and igniting until the whole is perfectly white. This method is very rapid, requiring but 20 to 30 minutes for large samples. It can be used with widely varying types of plant material. There is no danger of spattering and consequent loss of material, it produces no disagreeable fumes, and the residue is rapidly and easily decomposed and brought into solution with dilute nitric acid. In the process of ignition the silica is completely dehydrated and may be filtered out, or if the amount is small, that step may be omitted as i t does not disturb the accuracy of the determination which follows. As many as forty or fifty total phosphorus determinations may be carried out on plant materials in a day using this method of ashing. TABLEI. RECOVERY OF PHOSPHORUS ADDEDTO BLANKSIN CALCIUM CARBONATE METHOD BASEUSED ACIDADDED (1 cc. (1 cc. h 0,000207 . c 0.000204 P SAMPLE GRAMP) GRAMP) RECOVERED cc. cc. Graln 15.9 10.0 0.0012 9.0 0.0017 17.3 4.1 0.0023 15.3 0.0027 6.9 20.0 4.3 0,0033 20.3 7.4 0.0037 25.3 0.0046 3.0 26.0
P ADDED Gram 0.0011 0 0017 0 0022 0 002s 0.0033 0.0039 0.0046
DEVN. Gram +0.0001 0.0000 4-0.0001 -0 0001 0.0000 -0 0002 0.0000
-
TABLE 11. COMPARATIVE PHOSPHORUS CONTENTOF DRIED GROUNDCORNBLADESBY Two METHODS (1-gram sample used) MAGNESIUM NITRATEMETHOD CALCIUM CARBONATE METHOD KOH (1 cc. KOH (1 cc. c 0.000207 h 0.000207 SAMPLEGram P) Phosphorus Gram P) Phosphorus Gram CC. cc. Gram % % 0.0036 17.4 0.36 16.9 0.0035 0.35 16.9 0.0035 0.35 16.9 0.0035 0.35 16.0 0.0033 0.33 16.4 0.0034 0.34 17.4 0.36 0.0036 16.9 0.0035 0.35 16.0 0.0033 0.33 16.9 0.0035 0 35 17.4 0.36 0.0036 16.9 0.0035 0.35 16.9 0.0035 0.0035 0.35 16.9 0.35 16.4 0.34 16.4 0.0034 0.0034 0.34 Av. Std. devn.
0.347 0.012
Av. Std. devn.
0.346 0.004
PROCEDURE Weigh a 1-gram sample into a nickel or iron crucible and mix thoroughly with 2 grams of pure precipitated calcium carbonate. Shake the mixture firmly into the bottom of the crucible, then cover completely with a thin layer of calcium carbonate (1 or 2 grams usually suffice), and heat the crucible gently on a triangle with a Meker burner until fumes are no longer evolved. Ignite at the full heat of the burner until the residue is completely white. The first gentle heating decomposes organic substances, driving off all volatile matter and leaving a residue of carbon and the 1 This method has been in use in thie laboratory during the past 2 years. After oompletion of the present manuscript, the following note concerning a method using calcium carbonate for sshing plant samples came to the attention of the authors: Lepper, W., Landw Bwe -&a, 111, 159 (1930).
inorganic constituents of the sample. At a bright cherryred heat, the calcium carbonate decomposes to carbon dioxide and calcium oxide. The carbon dioxide unites with the residual carbon, forming carbon monoxide which burns off, leaving a white ash. The characteristic blue flame of carbon monoxide can be seen playing over the surface of the mass in the crucible. After the crucible has cooled, transfer its contents to a 250-cc. beaker. Moisten the ignited material with 25 cc. of water. Rinse the crucible first with water, then with dilute nitric acid, and again with 'water, adding the washings to the beaker. Then cautiously add dilute nitric acid with stirring until all the material in the beaker has dissolved. Add 3 cc. of nitric acid in excess. At this time, if the amount of dehydrated silica is large, it should be filtered. If it is small, it does not interfere in the subsequent operations. Then prepare the solution for the precipitation of phosphorus according to any of the usual methods, depending on the formation of ammonium phosphomolybdate. The time required from weighing out the sample until the solution kready for precipitation is usually from 25 to 35 minutes. TABLE 111. COMPARATIVE PHOSPHORUS CONTENTOF AIRDRIED GROUNDSOY BEAN SEED BY Two METHODS (I-gram sample used in magnesium nitrate method; ?-gram in calcium aarbonate) MAGNESIUM NITRATEMETHOD CALCIUM CARBONATE METHOD KOH (1 oc. KOH (1 cc. o 0.000207 0.000207 SAMPLE Gram P) Phosphorus Gram P) Phosphorus Cc. Gram 70 Cc. Gram % 0.0069 0.69 1 33.2 67.8 0,0140 0.70 0.0069 0.69 69.5 2 33.1 0.0139 0.72 0.0069 0.69 a 33.2 67.2 0.0139 0.70 0.0071 0.71 4 34.2 66.8 0.0138 0.69 5 34.6 0.0072 0.72 67.2 0,0139 0.70 0.0067 0.67 65.7 6 32.5 0,0136 0.68 0,0069 0.69 68.0 7 33.2 0,0141 0.70 Av. Std. devn.
0.693 0.015
Av. Std. devn.
0.698 0,012
TABLEIV. COMPARATIVE PHOSPHORUS CONTENTOF DRIED GROUNDTIMOTHY HAY BY Two METHODS (1-gram sample used) MAGNESIUM NITRATE METHOD CALCIUM CARBONATE METHOD KOH (1 cc. KOH (1 cc. c 0.000207 c 0.000207 SAMPLEGram P) Phosphorus Gram P) Phosphorus Cc. Gram % Cc. Gram % 9.1 0.0019 0.19 9.3 0.0019 0.19 9.2 0.0019 9.8 0.0020 0.19 0.20 9.1 0,0019 0.0020 0.19 0.20 9.6 9.1 0,0019 10.0 0.0021 0.19 0.21 0.0020 0.0021 9.7 0.20 10.0 0.21 0.0021 0,0020 10.0 0.21 9.9 0.20 9.5 0.0020 0.20 ' 10.0 0.21 0.0021 9.2 0.0019 0.19 Av. Std. devn.
0.195 0.007
Av. Std. devn.
0.203 0.010
In order t o determine the accuracy of the phosphorus determination using this method of ashing, several experiments were carried out. First, a series of blanks containing only the same amount of calcium carbonate as used in the determination were treated with varying known amounts of phosphorus in a standardized solution of microcosmic salt. The water was evaporated, the crucibles ignited, and the analysis carried out as described above. In each case the ammonium phosphomolybdate was thrown down a t 111
.
ANALYTICAL EDITION
112
65” C., digested a half hour a t that temperature, filtered, washed, and titrated. The purpose of this experiment was to determine if the large amount of calcium nitrate in the solution affects the recovery of phosphorus. The data are given in Table I. The small deviations in this table show that the various substances in the solution have no appreciable effect on the determination of the phosphorus present. In order to compare the results obtained by the calcium carbonate method with those obtained by the standard magnesium nitrate method, a series of phosphorus determinations were made by each method on samples of dried
Vol. 4, No. 1
corn blades, ground soy bean seed, and dried ground timothy hay. The results of these analyses by the two methods are given in Tables 11, 111, and IV. I t is apparent from these data that the calcium carbonate method is not only comparable in degree of accuracy with the standard magnesium nitrate fusion, but is also adapted for use with widely different types of plant material. No difficulties in manipulation were encountered in the calcium carbonate ashing of any of the three different plant materials used, even though they differ widely in physical and chemical properties. RECEIVED September 21, 1931.
_,
Determination of Substantivities of Dyes A General Method W. P.
AND
E. R. COHOE,39 Broadway, New York, N . Y .
THIS PAPER describes a general method if they were molecules. If this introduced originally by f o r obtaining the adsorption of any dyestuff is the case, we should accordingly in 1794 dm expect the adsorption characteron a n y fiber. Results have been procured by tinguish a class of dyes, has istics of a dye solution to vary in gradually come t o describe the Using the skin-friction machine l o obtain a set accordance with concentration. of dyeings made’ at known concentrations. A attraction which exists between a A reliable general method must long tapering dyeing is then made under constant take this last circumstance into dye in solution and a fiber it conditions, except that the dye is gradually exconsideration, because the atcolors. This attraction does not traction between a certain fiber appear to be to hausted. A comparison is made of the two and a dye in s o l u t i o n at one affinity, but, on the contrary, in recent years dyeing has been sets Of dyeings the recording concentration is not necessarily spectrophotometer. An integration leads to a classed as an adsorption phethe same at a different concennomenon. Later in this paper final curve which, for its characteristic portion, tration. The method to be described is designed to cover the it will be seen that the formof the is a sfraighfline on log paper. range of concentrations, which Obtained ‘Onfirms this tions of temperature, mercerization, speed, tightpoint of view. It is well known may be designated as the range ness of twist, and the like throw the CUrVe e i h Y of true solution. that for a particular class of fiber some dyes exhibit a greater afup or down but do not change its angle. I n exhaustion dyeing, where an e n d p o i n t o r a t l e a s t an finity than do certain others. For instance, in dyeing the vats Jade Green and Yellow G to- equilibrium may be reached, adsorption data are highly gether by the exhaustion method in a beaker, the latter color desirable and useful. I n continuous machine dyeing such does not attach itself to the fiber to any great extent until the data become a necessity. Here an equilibrium is never Jade Green is largely exhausted from the solution. Rough reached. White cloth is continuously entering the dye bath approximations of relative attraction, in the case of dyes color- and dyed cloth is continuously leaving it. If the constitution ing cellulose, may be made by placing drops of solutions upon of the dye bath changes, the shade so produced also changes. filter paper. In such cases, the dyed circle so produced is To prevent such changes, amounts of dyes equal to those resmall where the attraction is great, and vice versa; whereas moved by the cloth must be continuously fed into the dye the water ring surrounding the dyed circle is correspondingly bath in order to maintain a constant concentration. The continuous application of sulfur colors to cotton cloth wide or narrow. To obtain data relative to the speed of adsorption, it is has been carried on successfully in this country for a number possible, by dyeing a series of pieces successively in the same of years. In this case, the formulas of the make-up solutions dye bath each for the same fixed period of time, to obtain an have been worked out empirically. Because of the inferior idea of the adsorption characteristics of a dye. tinctorial value of this class of colors, together with a low With the advent of synthetic fibers, this divergence in substantivity, the problem here is unusually simple. Direct speed of application became so magnified as to lead Whittaker dyes, vats, and acid colors present an increasing order of (5) to classify colors according to substantivity, giving to each substantivity. As a result of studies upon the continuous a number designed to express its relative speed of attachment. application of these colors to various fibers, the desirThus those dyes, having the same numbers, attach themselves ability of reliable adsorption data became apparent, and a general method for obtaining them has been worked out. to fibers at similar speeds. Although each of the above methods affords a means of This method consists in determining and comparing the classifying dyes in accordance with their substantivities, it weights of various dyes which attach themselves to woven does not appear that a sufficiently accurate general method is fibers in a unit period of time under control conditions. It is so provided as to lead to a broad understanding of the adsorp- apparent that the mere immersion of a sample in a dye tion phenomena of dyes. At the present time it is generally solution*is not likely to yield satisfactory or accurate results. thought that very finely dispersed particles act in solution as By keeping the immersed sample in motion better results are HE term “substantivity,”
‘’
varying
