November 15,1934
I N D USTR I A L AN D EN G I N EER I N G CH EM I STR Y
Any fogging of the microscope lens due to water vapor resulting from the use of the cooling device may be easily remedied by withdrawing the microscope from its shield, drying, and replacing in position, but this procedure is unnecessary when the temperature of the block is above 100" C. The device is particularly useful in the case of high-melting compounds. The block may be heated quickly to within 10" of the melting point, the burner removed by withdrawing the rod, and a stream of water allowed to play on the bottom of the block for an instant. The rapid rise in temperature is thus brought to an abrupt halt within less than a degree. The burner may then be replaced, using a small flame so that the melting point of the compound is slowly approached. The device is also valuable in cooling the block rapidly when the melting point of a second and possibly lower-melting compound is to be determined at once. This feature is important if the apparatus is to be used by a large number of students. Among other advantages in the use of the apparatus are: absolute safety from accidents sometimes accompanying the use of sulfuric acid baths; extreme accuracy as regards softening point, sintering, change in color or crystalline form, and melting point range of compounds; the possibility of taking higher melting points; and the use of smaller samples. This last advantage is noteworthy in the determination of boiling points by a modified Siwoloboff (3) method. For this purpose a large capillary tube is used as a container for a fraction of a drop of liquid and a fine capillary tube, sealed in the middle, is introduced. The former is then inserted in the
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block as for a melting point determination and the same procedure is followed m in the ordinary Siwoloboff method. In Table I are given the melting points of some pure compounds observed by the use of this apparatus and by the usual sulfuric acid bath method. TABLE I. COMPARISON OF RESULTS MELT IN^ POINT
COMPOUND
By apparatus described
c.
By usual apparatus
c.
Cinnamyl alcohol 27-29 27-29 p-Nitrotoluene 51-52 51.6-52 Naphthalene 79-80 79-80 Benzoquinone 111-113 111-113 Benzoic acid 120-121 120-121 189-190 188.5-190 Succinic acid Diphenic acid 227-228 227-228 274-276 Anthraquinone 274-275 3-Aminophthalhydrazide 324-325 324-325O a Melting point taken by means of a copper block of the Berl and Kuhlman type ( 1 ) .
ACKNOWLEDGMENT Grateful acknowledgment is made to A. A, Morton of this laboratory for his interest in the construction of this apparatus and his assistance in the preparation of this paper.
LITERATURE CITED (1) Berl and Kuhlman, Ber., 60, 811 (1927). (2) Friedel, Bio&m. Z . , 209, 85 (1929). (3) Siwoloboff, Ber.,19,795 (1886). RECH~IVED June 16, 1934.
A Converted Air-Pump Shaker AVERYA. MORTON, Massachusetts Institute of Technology, Cambridge, Mass. OR laboratories which are supplied with compressed air simple shaking machine can be constructed from an
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air Pump, a set of door springs, and a suitable frame and platform. The general principle involved is the use of compressed air to drive the shaker forward, the release of the air pressure when the piston passes some holes bored in the barrel of the pump, and the return of the piston to its initial position as the result of the tension imposed upon the springs in the forward stroke, The construction in use in this laboratory, in which an air pressure Of lo pounds is maintained at the source, ifi illustrated in Figure 1.
which are mounted either on adjustable metal stands or wooden blocks so that the barrel is in line with the shaker latform. A set of door springs, 8,which are 0.44 incg in diameter X 12 inches (1.1 x 31 cm.) long [their osition is such as to make an 8 x 12 inch (20 x 31 cm.) rectan ye] are held between the top of a frame, F, and the base, B. dnly slight tension is needed. ~
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screw, since the latter has a tendency to work loose. The shaking platform is made and attached as follows: Between the front and rear pairs of springs two brass rods, threaded on each end and fitted with 0.625-inch (1.6-cm.) pipe holders, are attached. To secure a good grip a rubber stopper, bored to fit snugly, is first slipped over each s ring so that the ipe clamp is pulled down upon the rubber. T i e author's attacfment was An 18 X 1.75 inch (46 X 4.5 cm.) automobile hand air pump, made 3.75 inches (9.5 cm.) from the lower end of the spring. P, is altered as follows: The handle. is removed, a, and the end of It is obvious that a longer stroke is secured if the attachment is made near the center of the the rod is threaded and fitted spring, b u t because of t h e with a bearing connecting to nature of the frame used it was the shaking platform. The impossible to make a perfect cap is removed, b, to reduce adjustment at this point. A friction and noise. Four 0.19board is next mounted on these i n c h (0.5-cm.) holes, c, are brass cross pieces by means of drilled in the barrel at 90' intervals in a line around the U-fasteners or screws. Connection is made to the piston circumference 8.5 inches (22 rod of the ump as indicated cm.) from the bottom end of the before. A !ox or other suitpum . The size of the holes able receptacle may then be is of? more importance t h a n the osition because the leather fastened on t h e p l a t f o r m . The frame is made from 0.75wasEer of the piston will catch inch (1.9-cm.) channel iron in an opening that is too large. bent into the shape indicated The air valve a t the bottom is inFigure 1 and made rigid removed and the hole bored out to 0.25-inch (6.4-cm.) size, b y cross pieces. The whole a p p a r a t u s is mounted on in order to admit air rapidly a wooden base, 40 X 12 X to the cylinder. The recon1.75 inches (101 X 31 X 4.4 structed ump is held in place by two Erge pipe clamps, C, FIGURE 1 cm.)
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ANALYTICAL EDITION
Minor adjustments which may be made with each assembly are: moving the position of the barrel by sliding it through the pipe clamps, C, until proper release of the air is made a t the end of the stroke, increasing the number (but not the size) of the holes where air is released, increasing the size of the air inlet, and adjusting the tension and the position of the platform. When correctly assembled and regulated, the machine should start promptly with admission of air a t d, run continuously, and require no further adjustment for loads which vary from a gram to 1.5 kg. Higher weight limits have not been tried. The arrangement given in this description is for an apparatus in which only a few changes have been made with the starting materials. 1 ‘Since the stroke in this machine need
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not be more than 2 inches (5 cm.) long a t the most, it should be possible to cut down the length of the barrel and piston rod to proportionate size, reducing the apparatus to almost half the space formerly occupied. It should also be possible to mount the barrel under the shaking platform by use of suitable connections. The use of smaller springs will give a longer stroke. The same system of springs may be used with some advantage on motor-driven shakers. ACKNOWLEDGMENT The author is indebted to E. C. Curtis for valuable aid in the construction and assembling of this apparatus. RECEIYED June 20, 1934.
Apparatus for Measuring Adhesion of Dried Films R. P. COURTNEY AND H. F. WAKEFIELD, Bakelite Corporation, Bloomfield, N. J.
T
HE force of adhesion between two solids, limited in particular to the molecular attraction exerted a t the interface, has been and still is subject to more empirical than exact information, particularly when the materials concerned are organic films and metal surfaces. While it has been comparatively simple to determine whether two substances adhered to each other, it has been in only rather vague terms that we could describe how well or why they adhered. Further, there has been only empirical differentiation of the two factors of molecular and mechanical adhesion. The well-known classical researches of McBain and his coworkers gave us our first, most complete, and only systematic analysis of the fundamentals underlying adhesion. The determinations of adhesive strength were made by breaking joints by hand or by pulling apart in a tensile-strength machine. Within the limits of the determinations the data could be applied to the paint and varnish industry. This industry has been particularly concerned with these problems as they affect both wood and metal surfaces. Not only does adhesion play an important part in the weathering and age-resistance of a film but it is of great importance where mechanical flexing or abuse is encountered. Very satisfactory advances in the practical development of adherent coatings have been made using empirical tests, such as scratching with a thumb nail, lifting with a knife, or severe bending and crimping. The authors a t one time tested the adhesion of enamels to tin plate by pounding the sample with a certain hammer on a specific wooden laboratory floor. If the coating held until objections came from others in the laboratory, it was considered very adherent. It has been desirable to set up for the coating industry a testing method which would disclose the more minute variations in adhesiveness, would give more easily reproduced results, and would allow a more fundamental study of the phenomena to be made. An ideal test method would meet the following requirements : 1. It should be easily reproducible with similar coatings under identical conditions. 2. It should be adaptable to any organic or even inorganic film, 3. Normal drying or baking of the film should be possible. 4. The film should be uncha,nged by subsequent treatment prior to test.
5 . The test uhould not delorm or mechanically alter the film. 6. The test should be independent of the rate of application
of stress. 7. It should show adhesion at all parts of the area under test and should give a measure of the adhesion at each differential unit of the area whether of uniform adhesion or not. 8. Adhesion expressed in numerical terms should not be affected by changes in hardness, flexibility, elongation, or plasticity of the film or by the effect of internal friction as shown in the relation of slow or sudden bending or shock.
Several proposals have been made for measuring the adhesion of films to solid surfaces in mechanical units of force. Van Heuckeroth and Gardner (9)imbed a fabric strip in the film and measure the force required to strip the film from the underlying base. Gelva (8), in a method now being developed, cements a metal plug to the film after the film has dried on the base and measures the necessary rupturing force. Schmidt (6, 7 ) glues a wood block to the film, cuts the film a t the edge of the block, and, using a balance with water as the tare, obtains from a direct pull the force necessary for release in grams per square centimeter. Douglas and Pettifor (3) describe an “energy-absorption” test for the adhesiveness of glue to wood. A strip of strong webbing is glued to the wood panel and is then pulled off by a pendulum-type machine measuring the energy required for detachment. Christopher (8) describes the U. S. Bureau of Standards method for determination of the adhesiveness of bituminous coatings to steel in which a straight-pull method is used. Hart (6)has designed an apparatus which gives a measured impact to a coated panel and affords a comparative indication of the adhesion and brittleness. For determining the adhesive strength of surgical plaster there is a standard test in which a tensile-strength machine measures the force necessary to strip the tape loose from a plate, the force being applied to the tape in a direction parallel with the adhesive surface (1,6). These methods, valuable as applied to specific industries and giving in general interesting comparative results, have nevertheless certain limitations. In some the drying or baking of the film cannot be carried out under normal conditions. In others, the dried film may be changed by solvent or adhesive. In attempts to apply a load normal to the surface, the angle of applied force is apt to vary. The tensilestrength-of-bond method dependent on sudden application of stress may confuse brittleness with lack of adhesion. I n most
