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cating that the particles in this material must fit together perfectly. The particles apparently do not burst on coagulation, with the inner content flowing out to form a continuous hydrocarbon phase. On the contrary, dielectric measurements and water absorption studies show the presence of a continuous serum solid phase between the particles (19). Van Rossem (18) viewed the plasticizing effect as the bursting of the particles, with the result that their soft plastic contents become the continuous phase. This might appear to be a reasonable explanation, were it not for the fact that rubber breaks down only slowly, if a t all, when worked out of the oxygen contact. Busse (3) showed that plasticization requires oxygen and that mastication in air and ozone is an oxidation process. After milling, rubber disperses freely and completely in light petroleum solvents. This leads to the view that the tough gel skin on the particle is changed to a plastic form under the oxidizing and heating influences of milling. This change would take place most rapidly on the particle surfaces which are freely exposed to air and ozone during milling. The total amount of oxygen taken up during a half-hour breakdown on a cool laboratory mill is so small as to be undetectable by ordinary analysis. However, in certain hydrocarbon polymerization reactions oxygen can function either as a polymerization or depolymerization catalyst. Busse (3) showed that peroxides are formed in rubber during milling. Whether this peroxide formation in the hydrocarbon plays a primary or secondary role in the softening and plasticization effect on milling has not been proved. It is possible that hydroxyl groups are first formed, as is the case in most hydrocarbon oxidations. Hopkinson sprayed latex rubber breaks down more slowly than plantation sheet; this is explained by the fact that sprayed rubber contains a larger amount of antioxidant which protects the particles. I n this same connection it is known that rubber, freed from serum solids and antioxidant by coagulating it from highly diluted latex, breaks down quickly on the mill because of its more rapid oxidation. In presenting these views which are in some ways similar to
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those of Bary and Hauser ( I ) , possibility of the bursting particle mechanism of plasticization is not forgotten. However, on account of the extremely small size of these particles their bursting under milling does not seem likely ( 5 ) . The fact that oxygen is essential to the plasticizing process makes the gel-to-sol conversion mechanism through oxidation and heat seem best to fit the facts.
Acknowledgment Much of the experimental work given in this paper was carried out by H. J. Peters.
Literature Cited Bary and Hauser, Rev. gbn. caoutchouc, 1928, No. 42, 3. Belgrave, W. N. C., M a l a y a n Agr. J.,13,154 (1925). Busse, W. F., IXD. EXQ.CHEM.,24, 140 (1932). Caspari, J.Soc. Chem. Ind., 32, 1041 (1913). Cotton, F. H., Trans. Inst. Rubber I n d . , 6, 487 (1931). Feuchter, Kolloidchem. Beihefte, 20, 434 (1925). Fowler, D. E., IND. ENQ.CHEM.,Anal. Ed., 9, 63 (1937). Freundlioh and Hauser, Kolloid-Z., 36, 15 (1925). Hauser, E. A., “Latex,” p. 69, New York, Chemical Catalog Co., 1930. Henri, Victor, Compt. rend., 144, 432 (1907); Caoutchouc & gutta-percha, 3, 510 (1906). Kemp, A. R . , IXD.ENG. CHEM.,19, 551 (1927); Ibid., Anal. Ed.. 6. 52 (1934). IND. E&. C H E M . , ‘ ~643 ~ , (1937). Langeland, E. E., Ibid., Anal. Ed., 8, 174 (1936) Macallum and Whitby, Trans. R o y . SOC. Can., 18, Sect. 111, 191 (1924). Memmler, “Science of Rubber,” English ed., p. 115 (1934). Ibid., p. 117. Piddleston, J. H., J . Rubber Research I n s t . Malaya, 7, 117 (1937). VanRossem, Trans. Inst. R u b b e r l n d . , 1, 73 (1925). Vries, 0. de, I n d i a Rubber J . , 92, 13 (1936). Whitby, G. S., “Plantation Rubber,” p. 163, London, Longmans, Green & Co., 1920. Whitby, Dolid, and Yorston, J . Chevz. SOC.,1926, 1448. RECEIVBD Sepbember 20, 1937. Presented before the Division of Rubber Chemistry a t the 94th Meeting of the American Chemical Society, Rochester, N. Y., September 6 to 10, 1937.
Solid Matter in Boiler Water f-earning Additive Effects of Salts and Behavior of Gelatinous Precipitates’ LC. W.FOULK AND RICHARD ULMER, The Ohio State University, Columbus, Ohio
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HIS paper deals with the effect on foaming of various gelatinous precipitates under different conditions of precipitation, and gives some results on the foaming of salt solutions without the presence of solid matter; experimental evidence on the additive properties of salts in causing foaming is included. The apparatus and general procedures were those employed by Foulk and Brill (6). Priming concentration means the parts per million of dissolved salt in the boiler water when priming begins. (Prim1 Previous papers in this series appeared in IND. ENO.CHEM.,24, 277 (1932); 26, 263 (1934); 27, 1430 (1935). Nearly all experimental details have been omitted from this paper. They are recorded in Richard Ulmer’s doctor’s dissertation, 1936. The conditions under which this dxssertation may be consulted can be obtained from the Library of The Ohio State University.
ing as used here means any carry-over of liquid water in the steam.) The effect of suspended solids was measured by the difference between the priming concentration of a salt without suspended matter present and that of the same salt with the solid matter. Nine duplicate runs were made in each experiment to obtain a reliable average value (Table I). The priming concentration of calcium chloride deserves special mention because it is one of the salts used in the experiments on additive effect (given later), and because its priming concentration was the only one of the three salts tried that was not confirmed by a second experimenter. No explanation of this discrepancy can be offered. The salts used, however, were different specimens, and the individual results in the earlier experiments varied more among themselves than those
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INDUSTRIAL AND ENGINEERING CHEMISTRY
of the present study. Only one bit of objective evidence can be offered. Ryznar (7), working with another boiler, found that calcium chloride solutions surged up and down more than other solutions tried. TABLEI. PRIMING CONCENTRATIONS OF SALTS Substance in S o h . Sodium aluminate Sodium chloride Sodium carbonate Sodium hydroxide
Concn. a t Which Carryover Begins, p. p. m. 5619 4274-4235. 3946 2988-3151a
Substance in S o h . Sodium sulfate Calcium chloride Sodium . phosphate .
Concn. a t Which Carryover Begins, p. p . m. 2960
2886-2360a 2666
a These results were obtained by Foulk and Brill (2). The value 2360 is in Brill’s dissertation ( 1 ) .
Additive Effect of Salts In the paper by Foulk and Brill ( 2 ) it was assumed that the effect on priming of salts in solution was additive, and the data suggested nothing to the contrary. The following direct experiments, however, were made with two “bad” mixtures, with the idea that if these showed reasonable additivity other mixtures would do the same or better: EXPERIMENT I. A solution consisting of 50 grams per liter each of the chlorides of calcium and sodium was pumped into the operating boiler until carry-over began. An average sodium chloride value (2) of 4656 was obtained, which is 8.9 per cent higher than the calculated value, 4274 (2). EXPERIMENT 11. Mixtures of sodium aluminate and sodium hydroxide were used, because of the high priming concentration of the aluminate and the low value of the hydroxide, Three runs were made: Run No. 1 2 3
Ratio, Aluminate: Hydroxide 1:l 1:5 1:2.5
NaCl Value 3895 3870 4447
The results in runs 1 and 2 are about 9 per cent lower than the calculated values, and that in run 3 is 4 per cent higher. The results of the two experiments show that priming effects even with these “bad” mixtures are fairly additive. Readers should remember that a steam boiler, even a small experimental one, is a poor instrument for precise measurements.
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conditions of the experiment, magnesium hydroxide precipitates instead of magnesium aluminate. 111. ALUMINUMHYDROXIDE. The precipitate was prepared outside the boiler by adding 10 per cent sodium hydroxide solution to a hot 2 per cent solution of aluminum chloride until a distinct yellow color with methyl red was obtained. The mixture was then pumped into the operating boiler until carry-over began at a sodium chloride value of 3597, about 16 per cent less than was to be expected if the precipitate had not been present. The aluminum hydroxide, therefore, increased the priming. IV. FERRIC HYDROXIDE. An experiment carried out with sodium hydroxide and ferric chloride, according to the procedure described in 111, gave a value of 3040; thus, the precipitate greatly increased the priming. V. MAGNESIUM HYDROXIDE. Foulk and Brill (2) found that magnesium hydroxide precipitated in the boiler in the presence of an excess of sodium hydroxide reduced priming. The same effect was also reported by Peters (8). These results were confirmed by a new series of experiments, in which i t appeared that the priming-reducing effect of the hydroxide passed through a maximum with increasing concentrations of the precipitate. In view of the increase in priming brought about by pumping the hydroxides of aluminum and iron (111and IV) into the boiler, similar experiments were tried with magnesium hydroxide. Experiments were made in which the magnesium hydroxide was precipitated by adding sodium hydroxide to magnesium chloride. This form of precipitation is the converse of that used in the boiler, in which magnesium salt was added t o sodium hydroxide. The precipitate thrown down as described above and then pumped into the boiler greatly increased the priming as was shown by the fact that carry-over began a t a sodium chloride value of 3336. Without the precipitate, it would have been 4274. The results just given suggested an experiment with magnesium hydroxide precipitated outside the boiler by adding magnesium salt solution to sodium hydroxide. The precipitate prepared in this way and pumped into the boiler greatly reduced the priming. (This experiment was performed by J. W. Ryznar, National Sluminate Fellow for 1936-1937.)
Status of the Problem of Suspended Solids
An inspection of the evidence offered in this paper, along with that of Joseph and Hancock (6),Holmes (4),Peters (6), Effect of Precipitates Foulk and Whirl (S), and Foulk and Brill (W),shows that the I. CALCIUMPHOSPHATE. Solutions of calcium chloride effect of suspended solids on the priming of boiler water is not and trisodium phosphate were pumped alternately into the always the same. By experimenting with one kind of solid at a time, it has been found that some kinds increase priming operating boiler, always with the calcium slightly in excess. and others have no effect or actually decrease it. It has also Carry-over began a t a sodium chloride value for all salts of 3982, which is 7 per cent less than the calculated value, 4274. been shown that several kinds of solids, which a t first increase Therefore, it can be said that calcium phosphate precipitated priming, lose that property while in the boiler, and that the as above has little effect on priming. speed of such loss is greater, the higher the temperature of the 11. CALCIUMCARBONATE IN PRESENCE OF PRECIPITATE water. Finally, these facts have been found true both for FORMED BY SODIUM ALUMINATE.Two feed waters were used; solids introduced from the outside and for solids precipitated one contained sodium carbonate and aluminate, and the other inside the boiler. calcium and magnesium chlorides. These solutions were The contradictory statements in the past about the effects pumped alternately into the boiler with the carbonate-alumiof solid matter can now be understood. No one apparently nate mixture always in excess. An over-all sodium chloride thought that different kinds of solid matter might have opposite effects. It is no wonder then that in 1908 Stabler (8) value of 6569 was reached before carry-over began, thus showing that the priming was greatly reduced. How much of this wrote of foaming and priming of boiler water, “They are probably the least understood of boiler phenomena.” effect was due to the precipitated magnesium hydroxide and how much to the excess sodium aluminate (Table I), it is It has been assumed that gross carry-over (one per cent or impossible to say. more of water in the steam) is caused by a layer of foam on the The above experiment was planned to observe the effect surface of the water in the boiler reaching the steam outlet. of precipitated magnesium aluminate. Analysis, however, Experimental evidence of this will be offered in a subsequent showed that all of the aluminum was in the filtered boiler paper. Here it is necessary only to point out that it would be water; it would appear, then, that under the highly alkaline extremely difficult to account for the observed effects of solid
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matter on any other basis than the stabilization and destabilization of foam.
Speculations I n a previous paper (3) the loss of foam stabilization was ascribed to the lessening of the solid matter’s resistance to wetting. This was adequate for such substances as ground limestone, etc., but not for the effect of the gelatinous precipitates described in this paper. To account for their behavior it is proposed to study the effects of the electric charges on the bubbles and on the particles of the precipitates. That bubbles and solid particles carry electric charges is common knowledge in the chemistry of dilute solutions; it is, therefore, worth while to study the effects of the attractions and repulsions that arise from similar and dissimilar charges on bubbles and solids.
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Grateful acknowledgment is made to The Ohio State University Research Foundation and to The Ohio State University Engineering Experiment Station for their many courtesiey, and especially to the National Aluminate Corporation of Chicago for its generous financial aid in carrying on this investigation.
Literature Cited (1) Brill, doctor’s dissertation, Ohio State Univ., 1935. (2) Foulk and Brill, IND. ENO.CHEM., 27, 1430 (1935). (3) Foulk and Whirl, Ibid., 26,263 (1934). (4)Holmes, Trans. Am. Soc. iMech. Eng., R-P-54-5 (1932). (5) Joseph and Hancock, b. SOC.Chem. Ind., 46,315T (1927). (6) Peters, I r o n Steel Engr., 10, 117 (1933). (7) Ryznar, doctor’s dissertation, Ohio State Univ.. 1937. ( 8 ) Stabler, Eng. News, 60, 355 (1908). RECEIVED September 13, 1937.
Removal of Fluorides from Natural Waters by Calcium Phosphates W. H. MACINTIREAND J. W. HAMMOND Tennessee Valley Authority, Knoxville, Tenn. 1
The precipitation of solute fluorides as fluorapatite, 3Ca(P0J2.CaFz, from suspensions of active forms of tricalcium phosphate can be utilized to effect complete removal of fluorides from ground waters. Either ?extendedcold agitations, boiling, or filtration through sand-phosphate mixtures induces the fluoride removal. The most feasible procedure for small-scale operations is to introduce about 4 parts of either baking powder or superphosphate, preferably the cctriple’l type, into 1000 parts of water; then the dissolved phosphates are thrown out of the boiled solution along with the fluorides by addition of a small excess of calcium hydroxide, which in turn is precipitated by aeration. Either prolonged settling or immediate filtration removes the phosphate-fluoride precipitate. 1 The work here reported was done in the Chemical Department of The University of Tennessee Agricultural Experiment Station, Knoxville, in connection with fertiljzer experiments conducted under the ausBices of the Tennessee Valley Authority, Chemical Engineering Department; the senior author is connected with both organizations.
WOPE and Hess (11) recently reported results obtained by the use of an aluminic compound, Defluorite ( I ) , for removing fluorides from natural waters. The authors referred to findings that showed solute fluorides to be the cause of destructive mottling of teeth (7-10). Recent studies conducted a t The University of Tennessee Agricultural Experiment Station in collaboration with the Tennessee Valley Authority (3, 4) demonstrated that solute calcium fluoride will react with tricalcium phosphate to form fluorapatite : 3Ca3(P0& + CaFz ----f 3Ca3(P0&.CaF9 (1) This transition of solute fluoride to the insoluble combination with basic calcium phosphate resulted in dampened mixtures and in aqueous and carbonated water solution-suspensions of the phosphate and fluoride. It was effectively registered by (a) marked decrease in the solubility of the phosphate, ( b ) disappearance of the microscopic properties of calcium fluoride, and (c) the x-ray pattern of the synthesized fluorapatite suspensoid. Some of those findings and their relation to the observations of Hart, Phillips, and Bohstedt (d) and to the results on the divergent influence of limestone and dolomite upon leachate fluorides ( 5 ) prompted a lysimeter study of the reactivity between various phosphates, including meta forms, and calcium fluoride in the soil system. It was postulated that the variations in outgo of fluorides would afford a measure of the fixation of solute fluorides by the phosphates. It was further postulated that engendered fluorapatite may be a potent factor in the phenomenon of PZOSfixation in phosphated and limed soils.
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Removal of Solute Fluorides by Phosphate Suspensions I n the foregoing studies, the primary objective was to measure the decrease in phosphate availability induced by the
