A DEMONSTRATION WORKING MODEL OF THE FRASCH PROCESS FOR MINING SULFUR SAMUEL H. LEBOWITZ, TEXTILE HIGESCEOOL, NEWYORKCITY
This @per describes the construction and operatimz of a demonstration working model of the Frasch Process for mining sulfur. The model may be built, without any special skill, of upgaratus ordinarily available i n the secondary-school laboratory. It may be satisfactorily operated without danger from extremely high temperatures or pressures. . . . . .
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Need for Demonstrations of This Type Any chemistry teacher of experience is familiar with the difficulties of the average pupil in visualizing industrial apparatus and machinery. Diagrams, as a rule, fail to convey the necessary three-dimensional impression because of the pupil's lack of training in their interpretation. Due to this failure to understand the construction of the devices, it is almost impossible to make clear to such a pupil the operations that are carried out in them. In many cases, however, it is possible to build models which duplicate the constructional features of the commercial devices, hut are, unfortunately, inoperative. Such models, much as they may help for some purposes, are, however, far less desirable than others which not only indicate the construction of the industrial machinery, hut which also, in small-scale operation, duplicate the processes to he demonstrated. It is the purpose of this paper to describe a demonstration of the latter type. The model described has the further advantage that it may readily he constructed of materials available in the laboratories of the average secondary school. Theoretical Considerations That Governed the Design The Frasch Process is well known and is considered of sufficient importance to be mentioned and described in many high-school texts on general chemistry. Without going into a detailed discussion, it may he seen that one of the essential steps is the melting of sulfur undergonnd by superheated water at a temperature of 168 degrees Centigrade and a correspondingly high pressure. I t is apparent that the use of the pressure necessary to superheat water to this temperature would preclude the employment of glass apparatus, and would necessitate the construction of devices of great physical strength. In order to avoid the danger accompanying such high temperatures and pressures, it was thought advisable to substitute for the sulfur a material which resembled it sufficiently to give a satisfactory impression, but which would melt at a much lower temperature. The material finally chosen as meeting these requirements was paraffin, which was dyed to a suitable yellow color by the admixture of some strongly colored yellow wax candles. Oil-soluble dyes of the type used in preparing these candles would, if available, serve to color ordinary paraffin for this purpose. 1630
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It was found that glass tubing of sufficientlylarge diameter for the outermost of the three casings characteristic of the Frasch Process was not to be had in either of the laboratories with which the author is connected, nor was i t believed to be readily available in any ordinary secondary school laboratory. A survey of the apparatus on band disclosed the fact that a Liebig condenser might easily be adapted for use in the model apparatus.
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AUGUST,1931
Construction of the Apparatus The accompanying photograph and diagram show the apparatus as finally developed and used by the author. A wide-mouthed bottle (D) 6lled with lumps of yellow paraffin serves to represent the underground deposits of sulfur. The lower rubber connection is removed from a Liebig condenser of the separable type (C). The cork of the wide-mouthed bottle is bored to fit the lower end of the condenser water jacket. Both the inner tube and water jacket extend into the wide-mouthed bottle. A third tube, to carry compressed air, is then introduced, as shown, through the center of the condenser. T h i s t u b e passes through a two-hole rubber stopper a t the upper end of the condenser. A delivery tube is provided through the second hole of the stopper to conduct the materials raised to a second wide-mouthed bottle, representing the storage bin. The upper inlet of the water jacket is connected to a source of steam supply, which is, in this case, a copper boiler; and the lower outlet tube is closed off by means of rubber tubing and a screw clamp as shown. Operation of the Demonstration Steam is introduced into the outennost tube, i. e., the water jacket, of the condenser and passes into the wide-mouthed bottle through the narrow space between the condenser jacket and the inner condenser tube. The paraffin melts gradually and accumulates a t the bottom of the bottle. When a sufficient amount has melted, the compressed air is turned on. This may be done by blowing through the central tube or by the use of some other source of air under pressure. The paraffin(su1fur)-water-air mixture then rises through the intermediate tube and passes by way of the delivery tube to the storage bin. Pebbles added to the paraffin will not be affected by the steam, and will therefore demonstrate the effectivenessof the process in purifying the
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sulfur and will help to explain the great purity of the substance when mined commercially in this way. The apparatus may be cleaned by continuing the passage of steam for a short time after the paraffin has been raised and the compressed air turned off. Conclusion The demonstration as described duplicates all the essential features of the Frasch Process, including the three concentric tubes, the melting of the material underground, the elimination of impurities because of their higher melting points and densities, and the forcing of the material to the surface by the action of the compressed air to produce a lighter product which may be lifted by the combined steam and air pressure. Acknowledgments The author wishes to acknowledge the assistance of Mr. Joseph Glanz of the Yeshiva College, New York City, in preparing the original model; and of Mr. Robert Remingtou of the Textile High School in drawing the accompanying diagram.
