INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1923
chamber, Means are provided for periodically removing the stain with bleaching-powder solution and restoring operation when the impurity has been removed. Arrangements for using other tests for arsenic have also been devised. The selective absorption of colored substances for monochromatic radiation affords another very direct means for
FIG.4
detecting and eliminating impurities. An apparatus for this purpose is illustrated diagrammatically in Fig. 5. For instance, if it is assumed that the undesirable constituent is ferric iron, ammonium thiocyanate might be employed as the reagent. By the use of a color filter excluding red rays, the light-sensitive cell will be normally subjected to light only of other colors. When, however, ferric iron is present in the sample, a red coloration, capable of transmitting only or chiefly red rays, will appear in the transparent vessel. As no red rays are present in the incident light, it will be totally out off from the light-sensitive cell, thus increasing the cell resistance and operating, through a relay, the appropriate valve lor by-passing the product for further treatment. For simplicity in illustration, this device is shown as operating continuously. In practice, however, the apparatus will be
WFPRSS
-
k U i V N m C SAmPL/NG 5€Y/Cf
FIG. 5
arranged for intermittent operation, with provision for flushing out the cell after each test. The control of processes involving the neutralization of acid or alkaline solutions by the use of the selective absorption of indicators is but one of the large number of subgroups of possible application of selective absorption. Considerable attention has been devoted, especially by Houston, Hutchinson and Hurlbut, and Prideaux, to the study of the relation between the wave lengths and absorption coefficients of a limited number of inorganic and organic
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substances over considerable ranges of concentration and temperature. Further determinations of absorption coefficients, especially for various chemical indicators, would appear to be a contribution immediately useful in the design of control apparatus. In cases where it is found that a substance is not completely specified by any of the foregoing properties, it will be found in many cases that a combination of tests, such as a color test with a reagent, and of the index of refraction will serve to completely identify the substance. Among other possible applications studied, which do not come entirely within any one of the foregoing classes, may be included those of combinations of the preceding methods of control with automatic specific gravity regulation in such processes as oil distillation where both specific gravity and color of the product are of importance, replacement of complicated mechanical movements, by electrical devices controlled by light-sensitive means and of the utilization of the photo-electric method in connection with a suitable optical pyrometer for the control of high temperature operations. It will be observed that in most of the foregoing cases, apparatus in common use is adapted to the control of the process, with only such alterations as are necessary to make the testing or checking process a continuous one. Among the more usual means for checking the chemical composition of substances are chemical reagents and indicators, the polariscope, the colorimeter, the refractometer, and the spectroscope, while such physical properties as tensile and compressive strength, hardness, density, structure, temperature, and pressure are checked by testing machines, the scleroscope, the hydrometer, the microscope, the pyrometer, and the manometer. A study of these means of checking properties of substances shows that the greater number of them, especially those for checking chemical composition, may be registered by optical means in such a manner as to provide the appropriate impulse through the medium of the photosensitive cell to operate an electric relay. The complete development of the possibilities of process control through light-sensitive means involves the selection or development of analytical tests most suitable for affecting light-sensitive cells, the improvement of photosensitive cells, and the solution of such chemical or mechanical problems as might arise in the application of the control to the actual process. The suggestion is ventured that such development of this field may prove an inexhaustible source, not only of industrial improvements, but also of lateral scientific results of fundamental value.
News from Canada Success is attending the development of acetylene black at Shawinigan Falls, the Canada Carbide Company having marketed some quantity, which is finding a favorable reception by the paint trade. The power concentration of the St. Maurice valley will, we are advised, shortly be reinforced by development a t Les Gres, a fall about half-way between Three Rivers and Shawinigan. This is expected to develop in the neighborhood of 200,000 additional horse power for the Shawinigan Water and Power Company. The Canadian China Clay Company a t St. Remi, Quebec, has been investigating the possibilities of colloidal treatment of kaolin, and as a result is disposing of considerable quantities in the rubber industry. The suspension of the clay by colloidal means permits of the removal of impurities providing a specially adaptable clay for incorporation. Col. F. M. Gaudet, C.M.G., who has been Technical Executive Officer of the Honorary Advisory Council for Research, has resigned from that body and has joined the staff of the Canadian Industrial Alcohol Company.
