Proceedings of the American Academy of Arts and Sciences. VOL. XLVIII. No. 15. JANUARY, 1913. AN ELECTRIC HEATER AND AUTOMATIC THERMOSTAT. BY A. L. CLARK. INVESTIGATIONS ON LIGHT AND HEAT PUBLISHED WITH AID FROM THE RUMFORD FUND. (Continued from page 3 of Cover.) 1. 2. 3. 4. 5. VOLUME 48. BELL, LOUIS. On the Ultra Violet Component in Artificial Light. pp. 1–29. WALCOTT, HENRY P.- Alexander Agassiz. pp. 31-44. June, 1912. 30c, CHIVERS, A. H.- Preliminary Diagnoses of New Species of Chaetomium. pp. KENT, NORTON A.- A Study with the Echelon Spectroscope of Certain Lines in the Spectra of the Zinc Arc and Spark at Atmospheric Pressure. pp. 91-109. 2 pls. August, 1912. 50c. 6. KENNELLY, A. E., and PIERCE, G. W.-The Impedance of Telephone Receivers as affected by the Motion of their Diaphragms. pp. 111-151. September, 7. 8. 9. 10. 11. 12. 13. 1912. 70c. THAXTER, ROLAND.- New or Critical Laboulbeniales from the Argentine. pp. 70c. -Culture Studies of Fungi producing Bulbils and 40c. WEBSTER, D. L.-On the Existence and Properties of the Ether. 527. November, 1912. 40c. pp. 509 JEFFREY, EDWARD C.-The History, Comparative Anatomy and Evolution, of the Araucarioxylon Type. Parts 1-4. November, 1912. pp. 531-571, pls. 1-8. $1.00. 14. SANGER, CHARLES ROBERT and RIEGEL, EMILE RAYMOND.-The Action of Sulphur Trioxide on Silicon Tetrachloride. 40c. pp. 573-595. 15. CLARK, A. L. An Electric Heater and Automatic Thermostat. January, 1913. 20c. January, 1913. pp. 597-605. AN ELECTRIC HEATER AND AUTOMATIC THERMOSTAT. BY A. L. CLARK. Received October 9, 1912. 1 In a previous paper 1 I have described a form of electric heater and automatic thermostat for control of temperature, capable of a fair degree of accuracy and possessing a wide range. This has been improved recently so that the accuracy with which the heater may be maintained at any given temperature is very much increased. For the work described in the paper mentioned, it was not necessary to regulate more closely than 1/10°, but subsequent work developed the need for a higher degree of accuracy with certainty of operation, and with no sacrifice of range or capacity. The following is a description of the improved apparatus. It is given because this form of heater and thermostat seems to combine accuracy of control, ease of adjustment, wide range and large size of heating spaces as does no other at least the writer knows of none. As mentioned in the previous paper, the device is a modification of the thermostat used by Griffith 2 in his work on the Mechanical Equivalent of Heat. The essential features are as follows:- a cubical cast-iron box 15 cm. on an edge is made with hollow walls and bottom, the solid parts of the walls being 6 mm. thick, while the hollow space is of the same thickness. In this way a chamber is formed in the walls and bottom whose volume is 420 c. c. This is filled with mercury and forms the bulb of a gigantic thermometer, the tube of which is outside the apparatus. This cast-iron box with its enclosed mercury is surrounded by coils of German silver wire, and placed within a larger box for heating. The air in this space is kept in constant and rapid motion by a number of fans, so that the entire space is maintained at uniform temperature. This apparatus is lagged with magnesia and enclosed again in a massive wooden box. It is perhaps unnecessary to state that the body to be heated is placed inside the inner cast-iron box, which is provided with windows of ample size both in front and rear, as are also the enclosing boxes, so that observation is always possible. The outer windows have covers that may be closed to investigate effects of radiation. The mercury space of the inner box is connected by a steel tube with the automatic part of the apparatus which is shown in Fig. 1. 1 These Proceedings, 41, No. 16, Jan. (1906). |