ANALYTICAL CHEMISTRY
1506 With aged solutions of batch A and with pure barium chloride, the turbidity is perceived after a slight delay. The time lapse between addition of the reagent and perception of the first turbidity is much more pronounced with strontium sulfate and was studied with 0.01dl solutions of strontium salts and sulfuric acid. The turbidity became visible 20 to 30 minutes after combining the reagents if a solution of our strontium chloride hexahydrate was used. The time lapse increased to 1 hour if our strontium chloride hexahydrate was first rendered anhydrous by drying i n a n oven and then dissolved in water. Our strontium nitrate gave the visible turbidity within 2 to 5 minutes, but the time lapse was extended to 2 hours if the solution as acidified with hydrochloric acid and allowed to stand 2 hours before adding thr sulfuric acid. These strontium salts retained the described brhavior also after attempted purification by recrystallization from water. After the experience with the barium chloride, it does not seem proper t o attach any importance to the odd behavior of our strontium salts unless it mere proved that they are entirely free from impurities. Traces of barium could be responsible for the observed phenomena, and they would not be removed b j recrystallization from m t e r . All these observations show that the rate of precipitation and the particle size of precipitates may be strongly affected by tr-ic’e impurities in solutions. I n the instance of the barium sulfate, the particle size decreased by more than 50% without any noticeable change in the habit of the crystals of barium sulfate. Considering this remarkable sensitivity of the particle size, the analyst will do well to consider the origin and history of his solutions when trying to obtain easily filterable precipitates. I n addition, fine-grained precipitates might be contaminated bv the trace constituents which are responsible for the small particle size.
paper. The recrystallized salt, used in a 5 % solution, required 102 minutes for 28 mg. of barium sulfate t o settle. When this same solution was used 48 hours later, the barium sulfate took 49 minutes for 28 mg. to settle. These sedimentation results cannot be compared with those above, for they were carried out a t n lower temperature. It \vas suggested during the examination over my thesis that air was serving as nuclei. This was checked with a 5% solution: Standing for 1 hour a t 757.5-mm. pressure gave barium sulfate that required 47.4 minutes for 30 mg. to settle, standing over the same period of time but under 27.5-mm. pressure, with vigorous agitation every 5 minutes, gave barium sulfate that required 26.6 minutes for 30 mg. to settle. I have no doubt that impure barium chloride will cause fine precipitates of barium sulfate. I believe, too, that no one single item will explain all the interesting facts ahout this precipitation LITERATURE CITED
(1) Bogan, E. J.. thesis, Ohio State University, 1947. University of hIaine EDGAR J. BOQAN. Orono, Maine
Separation of Orthonhosnhates from Organic Phisphates
SIR: In attempting to follow the procedure of Martin and Doty [lIartin, J. B., and Dotv, J. H., ASAL. C H m f . , 21, 965 (1949)] for the separation of orthophosphates from organic phosphates, n e found that the aqueous phase developed a blue cwlor of greater intensity than the isobutyl alcohol-benzene phase. In an effort to eliminate this trouble, we prepared a new set of reagents, using only redistilled watpr and chemic& LITERATURE CITED of the highest purity. (1) Bogan, E. J., thesis, Ohio State Universlty, 1947. The persistence of a deep blue color in the aqueous phase (2) Fischer, R. B., and Rhmehammer, T. B., -4s.t~.CHEM.25, 1544 suggested that a contaminant in the ethyl alcohol used to rinse (1953); 26, 244 (1954). Queen’s College A. A. BENEDETTI-PICHLER the pipet was responsible. I n fact, addition of 1 ml. of absolde Flushing, N. Y ethyl alcohol to a mixture of 2 ml. of 4y0 ammonium molybdate in 4-V sulfuric acid and 0.50 ml. of stannous chloride caused a blue color to develop aithin a few seconds. The addition of 1 SIR: Benedetti-Pichler’s work on the “Effects of Impurities ml. of acetone gave a very intense blue color (absorbance > 2 upon Rate of Precipitation and Particle Size” is interesting. at 730 mp in a Beckman Model D U spectrophotometer with 1-cin. His conclusions on the aging and filtering of a solution of recryscuvettes), while 0.3 ml. of acetone gave a pale blue (absorbance tallized barium chloride dihydrate do not agree with mine. The 0 05). One milliliter of acetone-free methanol (as checked differences could well be explained bv the differences in the preby a mass spectrometer) had an absorbance of about 0.05 a t 200 cipitation. His conditions are: 0.02M barium chloride added seconds and about 0.15 a t 800 seconds. t o a solution 0.12147 in hydrochloric and sulfuric acids after a 5Methyl ethyl ketone, isopropvl alcohol, and isobutyl alcohol minute heating period compared to mine: 5% barium chloride also caused some blue color to develop. Formnldehyde and added to sodium sulfate in O . O O 4 N hydrochloric acid a t once a t ether did not cause the formation of any color. Heptyl and room temperature. Our filtering of the solutions was also difhexyl alcohol caused the formation of a bright yellow color in the ferent, his being filtered through S. & S. Blue Ribbon while mine aqueous phase, xhile cyclohexanone caused a yellow color in the was filtered through Pyrex F filters Tyith suction. cyclohexanone phase. In my work ( I ) , a sedimentation method \vas used t o comptre In addition to suggesting a rather sensitive method for acetone particle sizes. Barium chloride dihydrate, without previouh and possibly for some alcohols, these results explain the residual treatment, was used to make a 5% solution. After precipitation blue color in the aqiieous phase even after extraction of all the with this solution, 66 minutes were required for 28 mg. of barium orthophosphate. sulfate to settle. This same barium chloride dihydrate wap disJACOBJ. BLUM solved in hot water, filtered through a Pyrex F filter with suction, Navy Medical Research Institute and recrvstdlized. This salt \vas used to make a 5% solution. Bethesda, ’Id. The barium sulfate obtained required 48 minutes for 28 mg. to settle. This same 5 % solution of recrystallized salt was filtemd through a Pyrex F filter with suction. It was used within 5 minutes of the solution above and the barium sulfate took only 5.2 minutes for 28 mg. to settle. This last was not included in my thesis, for I felt that recrystallization had little to do with the effects on particle size. Also not included in my thesis was an experiment on recrystallization where the hot concentrated solution \vas filtered through
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