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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Before the installation of the treating plant there were a boiler maker and helper assigned to hot work, working on each eight-hour shift, and quite often they were unable to take care of all the work and it was necessary to assign another boiler maker t o hot work to help them out and get the engines ready for service. In addition, there was a boiler inspector on each eight-hour shift, whose duty it was to inspect all incoming engines and report conditions of flues, fire box, and front ends. The use of treated water has enabled us to dispense with the outside inspectors and their work is now handled by the hot worker in addition t o his performing all the hot work. Since the zeolite treating plant has been installed we have been enabled to reduce the boiler gang materially, affecting a saving of approximately $700 per month in labor alone. I am unable t o tell you a t this time just what the material saving Till be, but believe it will be many times that made in labor. The extended period for renewal of flues in switch engines alone
Vol. 20, No. 7
represents an item that, to my mind, will more than repay the cost of the zeolite plant. Another item that should not be overlooked is the fact that, with the use of treated water and the absence of leaks, it is not now necessary to blow engines down for washouts or caulking of leaks and we are enabled to double engines out when required. As t o the saving of fuel oil, I believe this will be another saving although I have no figures on this angle of the situation at the present time. I believe, however, through the elimination of scale on the flues, the saving in fuel oil should amount to a considerable figure. We also notice considerable benefit from the treated water on our road engines, as my attention has been called t o an engine now in service that has made over 60,000 miles since flues were last applied. This is considerably more mileage than we were able to get out of road engines using the raw Tracy water.
Municipal Water-Softening at St. Louis' August V. Graf WATER
DIVISION, DEPARTMEA'T
OF PUBLIC U T I L I T I E S ,
s
OFTENING of the St. Louis water supply was introduced with the use of sulfate of iron, just prior to the opening of the World's Fair at St. Louis in 1904. The Quincy process, as practiced a t Quincy, Ill, required only enough lime to hasten or insure the formation of iron hydroxide. At St. Louis a large excess of lime was employed, not with the thought of softening the water, but to aid coagulation. For most of the time no sulfate of iron was used, the coagulation and precipitation of the suspended matter being accomplished by the use of large amounts of lime with a resulting high caustic alkalinity. Later the amount of lime was reduced so that caustic water was rarely sent to the consumer. At present enough lime is added during the summer to convert all the bicarbonate alkalinity to normal carbonate before the addition of aluminum sulfate. I n winter, owing to the greater solubility of the normal carbonates in cold water, the lime is limited to an amount that will give a normal carbonate alkalinity that can be reduced to less than 30 p. p. m. by the amount of aluminum sulfate necessary to yield the desired floc for filtration. This limits the amount of softening that can be done in cold weather, and as a result the hardness of the tap water reaches its maximum during the winter. The reduction in hardness accomplished per grain of lime added does not depend alone upon the turbidity of the water, nor does it depend upon the temperature of the water. The effect of turbidity upon the consumption of chemicals has been noted by many water-works chemists and the added amount of lime necessary to accomplish the required softening of very turbid water has also been noted. Temperature might be an influencing factor in completely softening a water because of the greater solubility of the normal carbonates in cold water. I n partial softening, as practiced a t St. Louis, temperature is not an important factor. The hardness of the raw water also influences the amount of softening accomplished per grain of lime. I n partial softening the greater the hardness the greater the reduction in hardness per grain of lime. Whether this would be true of water completely softened with lime and soda ash, we do not know. The hardness of the river water varies from 126 to 257, average 177 p. p. m., and the reduction from 43 to 105, average 1 Received April 3, 1028. Presented before the Division of Water, Sewage, and Sanitation at the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 16 to 19, 1928.
ST. LOUIS, MO.
75 p. p. m. The reduction per grain of 85 per cent lime per gallon varies from 7.5 to 20.4, average 14 p. p. m. The amount of lime used varies from 1 t o 7, average 5.4 grains per gallon. When high color in the river water is accompanied by high turbidity, the water becomes extremely hard to clarify with lime and iron. At such times i t is necessary to add just enough lime to react with the sulfate of iron and to keep the water free from carbon dioxide when the aluminum sulfate is added. The amount of aluminum sulfate is increased to remove the color and also to coagulate the suspended matter passing the primary settling basins. Lime tends to fix the color and also to render colloidal the fine suspended matter and iron hydroxide so that, after 30 hours' sedimentation, the turbidity of the treated water is greater than the raw water. The milk of lime, added to the water, is prepared in the coagulant house and is made by weighing quicklime in automatic scales which dump a t set intervals into a circular slaking tank which is provided with revolving rakes. About 4 pounds of water are used for each pound of lime and a temperature of 200" F. is maintained in the slaker. The hot milk of lime overflows from the slaking tank, through boiler tubes in a heater tank, and the water used for slaking circulates around the tubes. In this may the temperature of the water is increased from 20" to 50" F., but it is still necessary to add steam t o the slaking water during a part of the winter to maintain the desired temperature in the slaker. When coagulating a very turbid water with lime and sulfate of iron, it will be found that by the time the turbidity has been reduced to a point where successful filtration is possible there will not be enough floc in suspension to furnish the gelatinous matter necessary for filtration. Aluminum sulfate is used a t St. Louis to give the required floc for filtration and also to aid in the reduction of normal carbonate alkalinity. It has been used since the filter plant was put into operation in 1915, so secondary or double coagulation is nothing new for us. During 1927 the average amount of aluminum sulfate used was 1.4 grains per gallon, and this was sufficient to furnish the necessary floc and also to reduce the normal carbonate alkalinity from 48 p. p. m. to 17 p. p. m., and the total alkalinity from 64 p. p. m. to 51 p. p. m. The bicarbonate alkalinity was increased from 16 p. p. m. to 34 p. p. m. The increase in bicarbonate alkalinity is due to the conversion of normal carbonate to bicarbonate by the carbon dioxide set free from the action of the aluminum sulfate upon the
carbonates in the water. The normal carbonate alkalinity of the water before filtration averaged 17 p. p. m. and after filtration, 15 p. p. m. With but few exceptions there is a decrease in the normal carbonate content if she amount present in the water applied t o the filters exceeds 4 p. p. m. Although the normal carbonate alkalinity of the water applied to the filters rarely exceeds 25 p. p. m., the filter sand has become badly coated. The amount of coating is now 16 per cent and the effective size of the sand has increased from 0.4 mm. to 0.54 mm. and the uniformity coefficient has decreased from 1.6 to 1.22 mm. The composition of the coating is as follows: Manganese dioxide Silica Ferric hydroxide Aluminum hydroxide Calcium carbonate
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INDUSTRIAL Ah-D ENGIXEERING CHEMISTRY
July, 1928
Per cent 0.04 0.4 12.9 17.3 45.7
Calcium sulfate Magnesium hydroxide Clay Organic matter
Per cent 0.3 10.0 12.4 0.6
If the normal carbonate content of a water is due to calcium carbonate and if the amount is much less than the theoretical solubility of calcium carbonate a t the temperature a t which the water is filtered, it will be found that some of the calcium carbonate will be removed by filtration through the sand bed. Last year the reduction in total alkalinity, due to the use of aluminum sulfate was 13 p. p. m. or 9.3 p. p. m. for each grain. The magnesium content of the water is lowered by the use of aluminum sulfate, which may account for the greater reduction in alkalinity than theoretical. The p H of the river
water was 8.17, the treated water 9.40, after treatment with aluminum sulfate 8.64, and after filtration 8.62. The strainers a t the filters are mounted on concrete ridge blocks and are made of Tobin bronze of the following composition: copper 61.25, zinc 37.87, tin 0.75, lead 0.10, iron 0.03 per cent. The holes in the strainers are l/16 inch in diameter and many of them are clogged with matter having the following composition: Loss on ignition (less COz)
Carbon dioxide Sulfur trioxide Chlorine Silica Ferric and aluminuin oxides
Per cent 21.56 4.90 4.11 0.28 5.83 0.60
Per .. rent .. ..
Lime Magnesia Stannic oxide Lead oxide Cupric ovide Zinc oxide
2.53 1.02 0.83 1.32 2.00 54,80
Whether these plates are being corroded by the water, or whether the corrosion is due to electrolytic action set up in the plate itself or to the development of current by the flow of the water through the interstices of the sand and gravel and the holes of the strainers, has not been determined, but we believe that the last cause is most probable. All deposits form on the under side of the plate, the upper side is clean and free from any sign of action. The coating is soluble in hot ammoniacal ammonium chloride solution. which might be used to remove the coating if the heating of the solution in the filters did not offer too much difficulty. Dilute sulfuric acid will be tried this summer, and if the coating can be removed without too much action upon the concrete, it will not be necessary to remove the sand, gravel, and strainers.
Laboratory Apparatus for Preparing Duplicate Uniform Paint, Varnish, and Lacquer Films' J . C. Brier and A. M. Wagner* DEPARTMENT O F CHEMICAL ENGINEERING, UNIVERSITY
ESTS of physical properties of paint and varnish films are not difficult to make, but unless the data secured are comparable their value may be questioned. I n the literature are numerous tabulations of comparative experimental data which frequently are inconclusive because the data are really qualitative although expressed as quantitative. However accurately the experimental work may have been conducted, the fact that all the data have not been resolved to a correlative basis renders their value controversial and may even result in apparently contradictory evidence. For the comparative investigation of paint, varnish, or lacquer properties it is desirable to choose as the datum plane uniform thickness of all films involved, for if all the films to be compared, whatever their composition may be, are of identical uniform thickness, the resultant data become a t once significant and decisive. The construction of this device was started while attempting to check some previous work where i t was found requisite to duplicate some varnish films. This task was difficult of exact accomplishment because some of the conditions, especially that of film thickness, which obtained for the preparation of the original films were unknown. The best result that could be expected, therefore, depended upon films that were relatively, but not exactly, the same as those previously used. The situation was such as t o make the value
T
1 Received March 12, 1928. Holder of the Thomas Berry Memorial Fellowship for the study of protective coatings.
OF
MICHIGAN, ANN ARBOR, MICH.
of the check uncertain, and consequently to emphasize the necessity for some mechanical device that could prepare and duplicate films of the same uniform thickness. An almost equally important requirement to be satisfied by this device was the possibility of accurate weight determination of each film a t the moment of application. To do this, the volatile thinner present in the system had to be retained quantitatively during the process, for othernise the actual weight of the fluid applied could not be determined with el-en a reasonable degree of accuracy. Because the time rate of evaporatioB of volatile thinner from a fluid surface is the maximum a t the instant of application, decreasing asymptotically with time, it is impossible to secure an exact film weight by weighing immediately after application, for by that time an appreciable quantity of thinner will have volatilized. The best practice, obviously, would be to determine the weight used by differencing the original and the final weights of the sample from which the film was prepared, because by such procedure the surface exposed to the air could be kept relatively small and evaporation of volatile components accordingly reduced to a minimum. This fact was important in determining the ultimate manner by which the film was applied. It was evident from the start that a mechanical device was required which could be calibrated in such units that all mechanical adjustments necessary to prepare any film could be recorded. Then by readjusting the apparatus to the same units and by using the same material duplicate films
