June, 1925
I,VD USTRIAL A-VD ELVGIiVEERIiVGCHEXISTRY
compounding (the grinding is preferably done in a ball mill in a viscous nitrocellulose solution to which the hydrocarbon diluents are afterwards added), a good grade of “white enamel” is produced. This enamel is suitable for application to flat surfaces which do not encounter much bending or vibration and which do not undergo large expansion and contraction. But if such an enamel is applied to a thin brass plate, and after drying and aging the plate is S~OWIYbent double, the enamel will chip and splinter a t the point of strain. While the effect is enhanced by the presence of pigment, the same phenomenon is observable to a lesser degree in “clear” or unpigmented lacquers. Such a test is suitable for laboratory experiment; the conditions are merely accentuated to a slight degree beyond those ordinarily met in practice. Under less rigorous conditions, smaller proportions of plasticizers may be employed. If there is added to the initial lacquer mixture, dibutyl phthalate in quantity equal to about 80 per cent of the weight of the nitrocellulose, the brass plate may be bent double and straightened out a number of times without marring the enamel or perceptibly loosening it from the metal. At the same time the enamel containing the plasticizer is not softer than the unplasticized enamel-i. e., it is not easily marred, nor is it “sticky.” This, then, is the “plasticizing” function. But careful measurement of the film itself has not yet disclosed a true “elasticity.” When such a film is broken on a tensile strength machine it is observed that the presence of the plasticizer has reduced the tensile strength of the film and has increased the measurable elongation before fracture. The reduction of the tensile strength is of no practical significance in most cases, as a good lacquer film 76 X 13 X 0.08 mm. (3 X 0.5 X 0.003 inch) will show a tensile strength of from 350 to 1050 grams per square centimeter (So00to 15,OOO pounds per square inch) of cross section a t the breaking point. On the other hand, although the elongation of the film before fracture is increased by the presence of the plasticizer, there is no perceptible “snap back” or true elasticity. By using suitable plasticizer- it i q even possible to lacquer
569
flat metal plates in such a manner that they may later bc bent in fabrication without marring the lacquer. In addition to the increased plasticity induced by the presence of plasticizers in lacquer, these substances in general improve the flow or smoothness of the lacquer films, functioning, no doubt, in the same manner as high-boiling ester solvents such as butyl acetate. In some cases plasticizers are stated to improve the “gloss” or shine of lacquers, and this is perhaps partially due to their retardant effect on solvent evaporation. Durability is, of course, the final test of a lacquer, and the extremes of heat, cold, and moisture met by a lacquer film on automobile body constitute a severe test. The presence of a plasticizer in lacquer film imparts the plasticity necessary to permit the extremes of expansion and contraction without in any way marring or loosening the film. The presence of moisture produces a further difficult test. Some substances which seem ideally suited as plasticizers, and which do, in fact, produce a plastic lacquer and tend to render the film homogeneous and nonporous, nevertheless have the property of absorbing water. The action of such a film on exposure is most discouraging. The film itself alternately takes on and loses water with humidity changes and is thereby much deteriorated. On the other hand, dibutyl phthalate, butyl tartrate, the phosphate esters, and other suitable lacquer plasticizers actually add considerably to the life of the exposed film. Bibliography 1-Graebe, B e y , 16, 860 (1883) 2-Nobel (Newton), English Patent 15,914 (1894). 3-Goldsmith (British Xylonite Co 1, English Patent 13,131 (1900) 4-hfeister, Lucius, and Bruning, German Patent 127,816 (September 12, 1906) b Z u h l , English Patent 4326 (1901). 6-Lundholm (Nobel Explosives Co ), English Patent 14,231 (1901). ;-Lilienfeld, English Patent 492 (1907). 8-Zuh1, English Patent 8072 (1901) * 9-Zuhl, English Patent 4383 (1902) 1: See also Worden, “Technology of Cellulose Esters,” where data on the phosphate plasticizers are completely re\ reued
*
A Special Vacuum Distillation Flask’ By R. L. Shriner U N I V E R S I T Y OF ILLINOIS, U R B A N A , ILL.
THE course of some work involving the separation of ItnKvacuo certain solid fatty acids, it became necessary to distil a large amount of crude material. The ordinary Claissen flask could not be used because of the high boiling points of the compounds, since the hot vapors attacked the rubber stoppers, making it impossible to maintain c y ~ L a vacuum for any length of time. The flask shown in the diagram was designed and has proved useful in the vacuum distillation of high-boiling products. The apparatus2was constructed throughout of Pyrex glass carefully blown so as to avoid any thin spots a t seals or indentations. The ground-glass joints should possess considerable taper to prevent jamming and are lubricated with a mixture of talc and beeswax in order to hold the vacuum. The length of the fractionating column depends on the boiling points of 1
Received February 26, 1925 The apparatus was blown by Paul W. Anders of this laboratory.
the substances distilled and the degree of fractionation desired, a short column giving more rapid distillation but less fractionation than a long column. For material boiling a t 200’ to 300” C. a t 7 mm., 12 cm. of indentations was sufficient. The set-in side arm permits only vapor to pass over and prevents any liquid condensing on the side walls from running over into the distillate. The fractionating column of large diameter is placed in the center of the flask, instead of a t the side as in the Claissen type, in order to prevent the mechanical carrying over of liquid due to condensation with subsequent plugging of the side arm, which usually occurs a t the beginning of a distillation. I n this apparatus 2 kg. of material have been distilled under a vacuum of 5 to 7 mm., the final temperature of the Wood’s metal bath rising above 400’ C. with no sign of the flask collapsing. I,~nd
