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taken by the U. S. Public Health Service under the direction of Passed Assistant Surgeon Wade H. Prost has a twofold object. It is desired to learn primarily the extent and character of the pollution now entering the Ohio river, the capacity of t h a t river t o receive and dispose of pollution, and the effect of such pollution upon the waters of the river and upon the health and comfort of the riparian dwellers. Secondarily, and possibly of equal ultimate importance, it is hoped to establish certain basic data necessary to a general discussion of the principles of the selfpurification of streams. No such comprehensive investigation of a great river system has ever been made. I n addition t o chemical,. biological and bacteriological. and hydrographic studies of the river itself and of the polluting waters, the investigation will include sanitary surveys and epidemiological studies of the bordering communiCONCLUSION ties and engineering studies of water supplies and sewerage I have shown how, in a national sense, the chemical industry systems. River pollution may be regarded from the point of view of contributes a very substantial portion to our national welfare and the useful part it plays in this work-a-day world, in the the river itself or of the health of the people dwelling upon its employment of persons, materials and of capital; how in a . banks. The sanitary qualities of a drinking water, and the broader sense it touches almost every field of human activity; effect of pollution upon riparian dwellers is essentially a biohow it is interwoven with the means required for the gratifi- logical question to be studied by biological methods, supplemented a t times by chemical methods. The question of nuicatioii of all our personal needs and desires. It needs merely t o be mentioned in mder to bring about a sance in a stream, although it deals with biological agencies, is full appreciation of the importance of the chemical industry essentially chemical and necessitates chemical or biochemical t o refer t o the important part it plays with respect to agricul- studies. The present paper deals solely with the chemical part of this tural chemistry. The chemical methods of investigation and investigation, as applied to the pollution and self-purificafion research applied t o agricultural problems indicate the requirement of certain materials by the soil, and these materials are of the stream. It will be pertinent, therefore, to present first, supplied by the chemical industry. I n that way the chemical a general statement of the problem as it appears in the light of industry contributes to the activity of the soil and the increased modern sanitary chemistry. The self-purification of streams is in no way a unique or reoutput per unit area of agricultural products. Conversely, as in the case of alizarin and indigo, hundreds markable process. It is essentially like the oxidation and deupon hundreds of square miles of the earth’s surface were de- struction of organic matter by the soil. In the case of a polluted stream, however, purification by oxidation is assisted by other voted t o the cultivation of the plants necessary to produce these articles. This very, large area is no longer required for factors, such as dilution and sedimentation, which together that purpose, and it is safe to say that in the chemical factories with the ideal conditions for oxidation which may exist, combine now producing these things the combined working area is under to produce such improvement that the phenomenon has ever been regarded as one peculiar to itself. four square miles. Right or wrong, I have always personally felt that had the botanist devoted the necessary attention to The reactions involved in this process are biochemical reactions. the growth and cultivation of indigo plant when the first syn- For their occurrence it is necessary to bring together oxidizable thesis of indigo was announced in 1880, the displacement of organic matter, oxygen and oxidizing bacteria The first and vegetable indigo between 1897 and 1900 by synthetic indigo last are necessarily present in polluted waters. The questions would not have taken place, or at any rate, it would-not have been of stream purification and prevention of nuisance, therefore, accomplished after so brief a struggle. The botanist has assisted reduce t o one of oxygen supply. wonderfully in increasing the alkaloidal content of cinchona The ultimate source of the oxygen available for this work is barks, and in the discovery of a large number of new plants the atmosphere. Cnder normal atmospheric conditions and a t capable of producing a latex suitable for India rubber production any given temperature, water dissolves a specified quantity of and he has also contributed greatly t o the development of oxygen which, unfortunately, is known as the saturation value. plantations, wherein the yield per unit area is much increased. This incorrect usage has resulted in serious misconceptions of While at the present day it may not be commercially profit- the true solubility relations of oxygen. Since the solubility of able t o produce synthetic rubber, or synthetic camphor, or any gas is proportional t o the partial pressure of that gas in synthetic nitric acid, or synthetic ammonia, yet it is perfectly the atmosphere above, it follows that the solubility of oxygen in true that the very existence of these possible synthetic sources water is approximately five times as great under an atmosphere of these materials renders it less and less likely that there will of pure oxygen as it is under a normal atmosphere. Hence be any undue advance in the cost t o the consumer of these ar- “supersaturation” is readily obtainable. It is of frequent ticles; at any rate, the cost will not be advanced beyond a figure occurrence in nature in the neighborhood of green plant life where the synthetic process can achieve a reasonable profit. where the oxygen content of the immediate atmosphere, or of Chemical industry, therefore, not only provides for our present the gases rising through the water, is greater than in the normal needs, but acts as safety device against famine, shortage or undue atmosphere. It would be eminently desirable t o refer the solumonopolization of a number of vegetable and mineral products. bility of oxygen t o a pure oxygen atmosphere in which case the 90 WILLIAM ST., NEWYORK accepted saturation value would be reduced t o approximately 20 per cent; but usage has sanctioned the present method which CHEMICAL STUDIES OF T H E POLLUTION OF T H E makes it necessary for us to deal with “supersaturation.” OHIO RIVER1 A saturated water will obviously dissolve n3 more oxygen. B y EARLEB. PHELPS The extensive investigation of the Ohio river now being under- Atmospheric oxygen tends t o re-enter the water in proportion as the oxygen content of the water is lowered by the oxidation 1 Presented at the 49th Meeting of the American Chemical Society, of organic matter. The intensity of the driving force of reCincinnati, April 6-10, 1914. dition t o the sources of benzol of a source much greater and more dependable than any theretofore available The neglect of a laboratory boy t o maintain the temperature he was directed t o keep in a certain vessel, taught that laboratory boy nothing, but the chemist in charge following up this result, finally ended u p with a method of substituting sulfuric acid for bromine, thereby reducing the cost of production by over 50 per cent. In both of these cases, i t is very doubtful if a man having no training beyond that required in the production of the things with which he was directly concerned, would ever have made those discoveries. The attempt to make oxalic acid would have resulted in failure, and would have been so reported, the result of the laboratory boy’s negligence would have been dumped into the sewer, and a new start made along the original lines.
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aeration is a direct function of the lowering of this oxygen content. I t is a t a maximum in a completely deoxygenated water and this is the condition of maximum oxidizing work in any stream. This condition, howe-\-cr,is also one of maximum nuisance and is not to be tolerated. Such a n anaerobic stream gives off foul odors and is black and unsightly in appearance. It becomes a matter of some importance, therefore, to determine the miminum value which the dissolved oxygen of the stream may reach before conditions approach the nuisance stage. This point practically fixes the capacity of the stream in question to care for pollution. The lower the permissible oxygen concentration the greater the proportion of the initial dissolwd osygen of the water available for the oxidizing reaction, and the greater the capacity of the stream to reabsorb oxygen from the atmosphere. L7pon this question of permissible oxygen reduction there are many diverse opinions and very little real knowledge. It has even been held that any oxygen whatever will prevent conditions of serious nuisance. The present writer's experience has not tended to confirm this view. That condition of nuisance, for example, which makes a river undesirable for canoeing on a quiet summer evening by reason of sewage odors emanating therefrom has been found to result from a reduction to fifty per cent of saturation. Extremely offensive conditions, with foul odors and black appearance, have been found to he associated with 38 per cent of saturation. On the other hand certain streams which have ranged from 60 to 75 per cent of saturation have given t o the senses no direct evidences of pollution. This point needs further study and discussion. It is merely desired t o draw attention a t this time to its importance as one of the fundamental factors of the problem. The second and most important factor is the re-aeration. The rate of re-aeration of water depends not only upon the oxygen concentration existing a t the time but upon the vertical distribution of that concentration. Assume, for example, t h a t t h e . water is uniformly mixed and quiescent. Absorption at the surface leads t o a downward diffusion which in time establishes a gradient ranging from essential saturation in the upper film to the initial concentration a t some point below. The diffusion process becomes slower as the curve of distribution of oxygen becomes flatter. I n practice, quiescent water, even though i t start with zero oxygen concentration a t all points, will, except in shallow layers, come t o a condition of practical equilibrium with very low average oxygen Concentration. Beyond this point the diffusion process is so exceedingly slow as t o be quite negligible. hIixing of the water, after such a condition has become established, reestablishes the even distribution and allows the absorption to proceed toward a new condition of equi1ibriu.n. I t is apparent, therefore, that, as conditions depart more and more from the condition of complete quiescence, the rate of reaeration is increased accordingly. The departures frcm quiescence may he definitely stated, and are more easily conceived, as the average time between uniform mixings. This form of expression is used, not only because it gives a workable statement of.the degree of agitation in a stream, but because such a time factor appears in any formula for re-aeration derived from the laws of solubility and of diffusion. Such a formula was developed by William M. Black, Colonel, Corps of Engineers, C . S. A , , and the writer in an investigation of the pollution of liew York Harbor.' In that case it was possible to determine the average time between mixings from a study of the mixing effect of winds, vessels and tidal currents. The re-aeration calculated from this theoretical formula, using the determined time factors, was in close agreement with the actual values found during the subsequent year and thus gave satisfactory confirmation of the accuracy of the method. With the deep and relaI Report of Colonel William M. Black, U. S. A,, and Earle B. Phelps, on t h e " Discharge of Sewage into New York Harbqr," March. 191 1.
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tively quiescent waters of New York harbor re-aeration was found to he almost a negligible factor. The capacity of such a body of water to oxidize pollution is practically limited by the amount of available oxygen brought in from the ocean with each tide. Under river conditions matters are directly reversed. The initial volume of available oxygen is small compared with the total capacity of the stream to oridize pollution. Re-aeration in rivers is the chief factor. The time between mixings, instead of being measured in hours, is probably measured in minutes, so t h a t its actual determination from direct observations cannot he made with even workable precision. It becomes necessary, therefore, to reverse our process of reasoning, to learn by suitable methods the actual extent of re-aeration, and, from those data, to derive the time factor in the original aeration formula. This factor will vary with the depth, character of the river bed, and rapidity of flow. It will differ, therefore, for various rivers and for various sections of each river hut should he similar for similar types of stream. If it can be determined for a sufficiently large number of typical stream stretches, it may be possible to deduce general formulas which will be applicable t o other streams of similar type. This, then, is the second important factor t o be investigated in our stream studies and if it can be satisfactorily determined it should be possible to estimate the capacity of a given river to dispose of pollution without objectionable results, or, conversely, the effect of any stated pollution upon a river of given type. The actual rate of re-aeration in a polluted stream cannot, unfortunately, be determined directly. I n spite of re-aeration a stream a t any given point may be losing oxygen, or it may be in oxygen equilibrium, since a t all times the biochemical reaction tending to reduce the oxygen is opposed to the actual re-aeration. It is necessary therefore to develop suitable chemical methods for the separation of these opposing tendencies. Consider first an ideal situation with two sampling stations on the stream between which stations there is no increment either to the pollution or t o the volume of the stream. These conditions cannot, as a rule, be obtained and it is necessary t o make suitable correction for the interference of additional pollution or additional dilution. The oxidizing reaction has been studied in the laboratory sufficiently to show that i t follows a fairly definite course and like all biochemical reactions is essentially monomolecular in its order. This means that it proceeds a t a constant rate or velocity so t h a t the concentration of oxidizable material decreases as a logarithmic function of the time. A sample of the water from the upper station is submitted t o study for the determination of three things: ( I ) The available oxygen which it contains; ( 2 ) the total amount of oxygen which will be required for the completion of the oxidizing reaction, known as the oxygen demand; (3) and the velocity with which that reaction proceeds. The sample from the lower station is submitted t o the same examination. Since any loss of available oxygen by oxidation must give rise to an equivalent loss in the oxygen demand, the difference of these two terms would remain constant throughout the course of the reaction, in the absence of re-aeration. Any increase in dissolved oxygen a t the lower station over the value calculated from the results of examinations at the upper station is therefore due to aeration. Correction for additional pollution or dilution between the stations is next made by means of the velocity of reaction determinations. From the determination a t the upper station and the known time required for water t o pass from one station to the other, the concentration of reacting substance a t the lower station is calculated. With increasing dilution the concentration is decreased, while with increasing pollution it is increased. Any change in the concentration, calculated from an assumed constant velocity of reaction indicates a n equivalent change in dilution or pollution between these stations. It is obvious t h a t
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these two factors are opposed t o one another in a plus and minus sense and t h a t if the added water were of the same character relative to its pollution as the water under investigation, the correction factor would disappear. I n brief, from the known constant velocity of reaction, stated in terms of physical chemistry, are determined changes in the concentration of the reacting substance, namely, pollution. The actual laboratory teehnique of these determinations is simple. The usual dissolved oxygen determinations are made upon a freshly collected sample; a second sample is incubated a t 20' C. and a dissolved oxygen determination made upon it a t the end of any convenient period, usually 24 or 48 hours. The difference between these two results is the oxidation that has taken place in the interval. Knowing the form of the reaction curve one computes from this, first, the velocity coefficient of the reaction and then, by extrapolation to a very long time, the total oxygen demand of the polluting organic matter. These two determinations a t each station furnish the required data, b u t there are many points that require special attention. It is necessary in the first place to secure an adequate sample of the entire cross section of the stream. This involves the careful selection of sample stations and the sampling of a stream a t various points in the cross section both vertically and horizontally, It is desirable in the second place to select stretches involving a minimum correction for additional pollution or dilution and it is quite necessary finally t o consider the effect of sedimentation. This can be arrived a t only by a study of the surface of the river bottom. A special apparatus is necessary for the withdrawal of the surface deposit from a given area of bottom and it is necessary t o make a careful survey of the river bottom between stations from time to time. A new reaction velocity must be 'iletermined for this deposited material and suitable correction made to the average findings in the water above for the period between the two bottom mud surveys. Finally the temperature of the river is not that at which the incubations are made. The temperature coefficient of the reaction must be known and suitable correction applied. It will perhaps be noticed t h a t no attention has been given in the foregoing discussion t o the supposed relation between concentration of sewage in water and probable nuisance. This factor has heretofore been the chief theme in any discussion of stream pollution and self-purification. Recognized authorities have variously estimated stream flows of from 2 . 5 to 3.5 cubic feet per second per thousand persons contributing, as the danger line. A still less correct statement is often made in that sewage dilutions of from I in 16 to I in 23 will undoubtedly produce nuisance. A little consideration of the true factors of selfpurification will show that any such form of statement is entirely incompatible with the facts. A deep quiescent swimming pool may become putrescent even with the slight amount of organic pollution which it receives. A one per cent dilution of sewage in water will often putresce under laboratory conditions. Deep and slow-moving bodies of water such as are found in canals or in rivers behind dams, especially if they be protected against wind action, have very little capacity for re-aeration and are in consequence much more affected by sewage than rapidly running and relatively shallow streams. The maximum oxidizing work occurs under conditions of minimum depth and maximum agitation. Any discussion, therefbre, of permissible concentration of sewage in water without reference t o the character of the stream in question is futile and misleading. It is proposed to study by the methods outlined the rate of reaeration of the Ohio river a t a great many points, but particularly below the three points of greatest pollution, namely, Pittsburg, Cincinnati and Louisville. In none of these cases are the conditions ideal and i t will be necessary to do a large amount of work t o obtain results of satisfactory precision. As an additional check upon results it is also proposed t o make as thorough
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a study as practicable of the actual polluting material entering the river a t these three points. The total oxygen demand and the velocity of the oxidizing reaction will be determined upon this initial pollution in a manner 'similar t o that which has been described. I n case of concentrated organic matter, the methods are modified by first diluting in suitable proportions with aerated water. Further checks upon the work involve similar studies upon the tributaries and upon pollution from smaller communities between stations. Moreover, instead of the two stations which have been used in illustration, the work will actually comprise a chain of stations for regular study. I n addition, connecting data will be obtained by means of house boat laboratories. The three regions of maximum pollution are fortunately of three distinct types. The river below Pittsburg is a series of short pools separated by shallow water flowage. Below Cincinnati there is a long quiescent stretch in which sedimentation will be a n important factor. At Louisville there are rapids giving a minimum of sedimentation and a maximum of aeration. Certain special minor points such as the effect of low temperature upon aeration and the effect of long quiescent stretches uFon sedimentation will also receive special study. It is anticiFated as a net result of this chemical portion of the Ohio river investigation t h a t sanitarians will be in a position t o discuss with much more assurance than a t present the general principles which underlie the phenomenon of the self-purification of streams. HYGIENIC LABORATORY U S PUBLICHEALTHSERVICE WASHINGTON
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THE APPLICATION OF PHYSICAL CHEMISTRY TO INDUSTRIAL PROCESSES' B y WALTERF RITTMAN
The luxury of today is the necessity of tomorrow; likewise the theory of today is the practice of tomorrow. Gayley's process of drying air for a steel furnace, the various nitrogen-from-air processes, the contact process of manufacturing sulfuric acid, synthetic indigo, synthetic tanning materials-all were in the field of abstract theory but a few years ago. Today they are practical realities. Similarly, many of the theoretical principles and processes of today will, in all probability, be realities a few years hence. The invasion of chemistry by physics, and the production of what is known as physical chemistry, promises t o be a most important basis for progress in the field of applied chemistry. Whereas physical chemistry is often looked upon as one of our most theoretical subjects, it will be found to be one of our most practical as well. I t s principles are useful regardless of the materials involved in the reactions, whether copper, steel, soap, glass, cement, gas, textile, or any other chemical product. Physical chemistry is described as that branch of chemistry which has for its object the study of the laws governing chemical phenomena. When these laws and their application t o a reaction or process are once understood it is a relatively easy matter to select the most favorable physical conditions. The task of the chemical engineer is to produce these most favorable working conditions in an apparatus which operates on a n industrial scale. A further advantage of a knowledge of theoretical principles and perhaps one t o be more frequently applied is the aid such knowlledge gives in avoiding fantastic so-called improvements. The chemical engineer rarely creates new products; he deals with processes and machinery which produce quantities economically. Obviously his problems often differ from those of the laboratory chemist. The fact that a reaction is slightly exothermic or endothermic is of secondary consequence in laboratory experiments, but in applied engineering this fact a t once del Presented at the 6th Semi-annual Meeting of the American Institute of Chemical Engineers, Troy, New York, June 17-20, 1914.
