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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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 at the temperature at 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 pH 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 at 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 at once significant and decisive. The construction of this device was started while attempting to check some previous work where it 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 at 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 at 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
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could be made. When identical films could be prepared from experiments the principle of the doctor or scraper blade apthe same material by such readjustment, the possibility of peared to be most feasible, primarily because spreading by the preparing films of any predetermined thickness, still using the use of a rigid bar insured uniform film thickness. The apparasame material, immediately presented itself. From this tus subsequently constructed (Figure 1) embodies this prinpoint it was but logical to anticipate the preparation of films ciple, modified to meet the other requirements placed upon it. of predetermined thickness from any kind of paint, varnish, Apparatus or lacquer. The practicability of doing these things with this apparatus has been satisfactorily demonstrated, and data The apparatus, illustrated by Figures 2 and 3, is composed will be submitted to substantiate this statement. of three essentially individual parts-the base, the arm, and The literature disclosed no method which answered the the basket. purposes sought in all respects. The one most generally BAsn-The base is composed of three parts-the grooved used to prepare films for test purposes is that of brushing, base plate, the slider plate, and the roller. which has the objections of varying thickness, loss of volatile The grooved base plate, cut from a cast-iron plate 40 cm. thinner during the application process, and impossibility long, 23 cm. wide, and 2.5 cm. thick, is provided with a of exact duplication. Stoppe13 has shown that flowing or central groove extending the length of the plate to a depth dipping yields a wedge-shaped film with the thick portion of slightly more than 1 cm. At the upper surface of the base at the lower edge. The loss of thinner and consequent ina- plate the width of this groove is 14.5 cm., increasing to 16 cm. bility of exact weight determination, the variation of viscosity a t the bottom. Both sides of the dovetail tongue thus formed, with different samples, and the difficulties of duplication4 together with the adjacent bottom to a width of 12.5 mm., eliminated this possibility. Gardner and Sward, employing are polished, the remainder of the groove bottom being a modification of the spinning method used by Walker and routed out slightly to allow clearance for the slider plate. Thompson, obtained films of fairly uniform predetermined The slider plate, also made of cast iron, is but half the thickness but had no way of accurately obtaining the film length of the base plate, 14 cm. wide at the top and slightly weight because both non-volatile and volatile matter were more than 1 cm. thick. It is mortised to fit the dovetail permitted to escape during the spinning operation. Davison’ tongue of the base plate and polished on the sides and bottom prepared films by pressing varnish between two similar disks, where contact is made with the polished metal of the base then sliding the disks apart in a vertical position and calcu- plate. By means of an adjustable take-up bar, C, fitted into lating the film thickness from the volume of sample used. one side of the dovetail tongue of the base plate, all lateral By this means an average thickness was computed but a and vertical play of the slider plate is eliminated; conseuniform thickness was not necessarily obtained, this objection quently it is restricted to unidirectional horizontal motion. alone eliminating it from further consideration. One end of the slider plate, which will be termed the “front,” Flotation on mercury was attempted but, although satis- is connected by a cable to a variable-speed pulling device factory for viscous liquids like collodion, a plastic paint would mounted on a separate base to prevent possible transfer of not spread uniformly under its own weight and could not be motor vibration to the apparatus. The rear end of the readily from the mercury surface. Even by slider plate is attached by cable to a counterbalance to reduce - separated . to a minimum anv shock superimposing a glass plate and vibration inc:dent to on the paint and applying the forward motion of the pressure, it was not possiThe necessity for a mechanical device to prepare slider plate t h r o u g h t h e ble to spread the paint unipaint, varnish, and lacquer films suitable for comparadovetail tongue of the base formly; consequently work tive studies of physical properties is pointed out. To plate. in this direction was abanbe satisfactory this device must apply films of uniform doned. Spraying immediThe surface to be covered over-all thickness without loss of volatile content ately suggested the disadwith a film, usually a recduring the process, with the possibility of duplication vantages of rapid loss of tangle of plate glass, is laid at any time by the use of any coating material. volatile thinner upon atomupon the upper surface of The available methods for preparing films for exi z a t i o n , t h e difficulty of the slider plate and mainperimental purposes are reviewed and are found to be producing an even film on a tained in place by a heavy inadequate. small area, and the impossirubber-covered cylinder A mechanical apparatus constructed to meet the bility of rigorous duplicawhich presses down upon it. above requirements is described. It embodies the tion. I n short, none of the This roller extends laterally principle of the doctor blade, with the addition of a methods generally used was over the slider plate and is basket attachment which completely encloses the entirely satisfactory for the r e t a i n e d a t e a c h end by fluid sample. This basket is sufficiently tight to purpose in mind and it beslotted posts, W , set into the prevent more than a negligible loss of volatile matter. came necessary to seek elsebaseplate margins 18 cm. Uniform thickness is assured by the doctor blade where for a principle upon from the rear end. which can be adjusted for height by a micrometer which to base the operation screw. Am-The arm serves to of the desired mechanical Experimental data are submitted to indicate the support the doctor blade, in device. possibilities of the apparatus. Uniformity of thickness its modified form called the After many preliminary for individual films, and for series of films prepared basket, in a rigid vertical with the same micrometer screw adjustment, is shown p o s i t i o n above the slider a Proc. Am. SOC. T e s t i n g to lie within the range of error introduced by the p l a t e . It is essentially a Mafcr4aZs, 28, I, 286 (1923). 4 Gardner and L e v y , A m . inequalities of the surface upon which the films are microscope arm with the Paint Varnish Mfrs. Assocn., Circ. prepared. The method used to make duplicate films b a r r e l removed, which is 808, 273 (1927). anchored in the margin of from any coating material is explained and illustrated. 8 IND. ENQ. CHEM., 19, 972 the base plate a t its middle. In conclusion, it is demonstrated that the loss of (1927). a Proc. Am. Soc. Testing Malevolatile material during film application is within the I n place of the barrel there rials, 22, 11,464 (1922). has been substituted a heavy limits of experimental error and therefore is negligible. 7 Paint, Oil Chem. Rea., 80, brass cylinder, D, to which No. 11, 10 (1925). ~~~
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
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justable blade may be rotated slightly with regard to the and lowered hy the focusing gears of the microscope arm. Near doctor blade. the top of t.he square brass plate, E , which extends across the The adjustable blade fits snugly between the two end slider plate, two bolts, F, with butterfly nuts have been set to plates of the doctor blade with a fluid-tight friction joint furnish suspension points for the basket; a t the center a assured when the tie rod is drawn UD. The end dates have threaded rod, G, with a thumb nut, T, extends through t.he sufficient width to provide tight j&ts over t h i entire are plate to the hack and provides for opening and closing the t,liat the adjustable blade may rnake while pivoting about the basket; at, t,lie bottom two set screws, H , have been adjusted doctor blade. At the top of the adjustable blade a pin, S, t o make contact with the doctor blade and thereby prevent is extended vertically which is inserted into a hole at the vibration of the basket by acting as a brace. Both t,he end of the threaded rod, G, thereby providing for opening and coarse, B, and fine, A , adjustment screws of the microscope closing the basket. Thus by turning up the thumb nut, T, ,win ham been retained and serve t,o regulate the vertical on the threaded rod, G, which works against the front of the arJn plate, the adjustable blade, K , functions as a lever operating over the two set screws, &, as fulcrums, regulating the opening a t themoutii of the basket. The mouth of the basket is considered as the bottom edge of the inverted prismand is the line of contact of the lower edges of the doctor and adjuvLable blades. The lower or scraper edge of the doctor blade iias a sound, flat surface, whereas that of the adjustable blade is beveled on the outer surface to prevent interference when the basket is opened. A vertical pin, U , set in the top of each of the 6-mm. extensions to the scraper edge of the doctor blade is located opposite a horizontal pin, V , protruding beyond a e h end of the adjustable blade and parallel to its outer surface, although projected slightly from it. By stretching selected rubber hands to their elastic limit and then weaving them Figure I-Rear View 01 F i l m Apparatus w i t h Rubber Remmed Irom Roller about the opposing pins, each end of the basket is provided with ample tension to hold the adjustable and doctor blades distance of the basket above the slider plate. Calihration together a t the point where the coincidental set screws and siiows that one complete turn of the fine adjustment (mi- sockets make contact, thereby forming a satisfactory and crometer) screw alters the vertical position of the basket by simple means for keeping the assembled basket together. 101.6 microns, making it possible to predetermine the thick- This makes disassembly for cleaning and subsequent reness of the wet film and consequently to duplicate films with assembly for use an easy task. little difficulty. Xasne'i--The basket (Figure 4) is the most important and intricate part of the apparatus. To provide for ease in cleaning it has been made up as a unit composed of three parts which can he assembled and disassembled easily. These parts are the doctor blade, the adjustment blade, and the cover. When assembled, the basket appears as an inverted right triangular prism 7.5 em. long and 4 em. high. Tlie sides of the prism are formed by the doctor blade, J (Figure 3), and the adjustable blade, K,both made of polished steel; the prism base, which forms tbe cover, L,of the basket, and the two end plates, N , are made of aluminum plate. The doctor blade, which faces the front when the basket i s in place, is constructed with two slotted guides, M , extending abobove its upper edge designed to fit the supporting bolts, F, near the top of the arm plate, E. In this manner the basket is suspended from the arm. The slotted guides provide a means for leveling the lower or scraper edge of the doctor blade to the prepared surface on the slider plate before ELEVATION rieidlv clamnine the doctor blade to the ann hydrawins.- UP. Flgure 2-Detail of Rear Elevation of Film Appar-stUs t & iutte& n&, F. The aluminum top is shaped so that it will lie on the upper The length of the doctor blade along the scraper edge has been increased beyond tbat of the main body of the blade edges of the two blades and fit between the purposely exby 6 mm. on each side. Because the adjustable blade is tended end plates with a reasonably tight joint. It is suffinot extended in this way, the chance of fluid "piling up" a t the ciently wide to allow for the motion of the adjustable blade ends of the basket is eliminated. Each end of the doctor and fits snugly enough to present only negligible openings blade is fitted with a right-triangular aluminum plate, N , through which any volatile matter in the basket-enclosed fastened perpendicular to it, the base of the triangle raised fluid may escape. 1.5 mm. above the too of the doctor blade and the aoex flush Manipulation of Apparatus is bolted a 9-cm. ,square brass plate, E , the whole heing rtiised
In order to put the apparatus in working order the slider plate is moved so that its front is directly under the microscope ann and a tared clean rectangle of plate glass, marked for identification, is placed upon it before superimposing the roller.
reached and t,he clutch disengaged when the film is completed. The plate glass with tlie film is immediately placed on a mercury bath to insure a perfectly horizontal drying surface. The basket is removed, replaced in the st,and, and the final weight obtained. Obviously, the difference between the original and final weights of the basket consiitutes the actual weight of t,hefilm. To clean, the cover is removed from the basket and the sample discharged. The rubber bands are then unwound irom the end pins, U and V , tu iree the doctor and adjustable blades, wliieh are carefully washed in a suitable solvent and dried. Reassemhly is accomplished by slipping the adjustable blade betm.een the end plates of the doctor blade with the respective set screws and sockets eo-incidental. By tightly weaving tlie rubber hands betrreen the end pins as before, the bssket is again ready ior use. Experimental Results Fiaure J---Drfsil of Section of Film A P P ~ T ~ and ~ U BBnsket
T h e asseinblcii b:tsket, supported in an upright position Iiy :in especially designed wire stand, is filled to t,he level of the t,ie rod, P, with tlie sample and then covered. Both skiid and basket are weighed on a balance and t,lie init,ial weight, is recorded. The weighed basket is immediately riispeuded, loosely, on the m u , E, from the supporting bolts, F ; with the vertical pin, S, oil the adjustable lhdc, X , dipped intu the opening proorided in the t,hreaded rod, G. With the fineadjustment screw, A , set a t zero, the basket i s lowered by turning the coarse adjustment screw, B, until the entire scraper edge of the doctor blade, J , rests on the surface of the phtc glass. The basket liaring been thus leveled by taking ad\-antage of tlie play alloxTed by the guides, M , on the dor-
tor blade, the butterfly nuts on the bolts, F, are drawn up,
