352
JOURNAL OF CHEMICAL EDUCATION
FEBRUARY,1931
only are the errors noticed but those bottles involved are evident as well. We have found that this method has reduced the usual mechanical errors to almost nil. I n recording or marking the bottles of the unknown one does not have a long set of numbers to deal with, as in the system suggested by Taylor at the Atlanta meeting of the American Chemical Society, nor tags t o lose or become hopelessly mixed (1). Using only three numerals together with aletter to represent the type of unknown, twenty-six sets of unknowns with 990 unknowns to the set can be prepared. 3. N o biased aid can be obtained by the student either wilfully or otherwise from the instructor, for our "key book" is unavailable except a t times of grading. The habit of shopping for the easy grading instructor or the instructor who will permit the "I think I got a test for" or "a sort of test for" reports is prohibited. Since all unknowns are graded by one individual and only a t stated intervals, the student must make a delinite decision from his own work. In the laboratory the instructors are a t liberty to give their own opinions since they know nothing about any of the unknowns except what the student has showed them. 4. T h e honesty of the student i s not inooloed, in that i t is impossible for any one other than the individual t o whom the unknown is issued t o make the report. The unknown, once reported for a grade, cannot be reported by other individuals as is possible under many systems. 5 . There is n o system to be handed down from class to class nor the method of analyzing the unknown from its number as in Taylor's method. G. The above method is flezz'ble enough t o meet local conditions and still be carried on successfully. Literature Cited (I)
FURMAN, "The Technic of Conducting the Introductory College Course in Qualitative Analysis." J. CHEM.EDUC..5, 950 (Aug., 1928).
Depths of Earth Yield Solid Carbon Dioxide. From the interior of the earth beneath Jackson county, Colorado, comes snow white, solid carbon dioxide, which freezes a t 70 degrees below zero Fahrenheit. Enough is obtainable iu one day to fill a train, Prof. F. F. Hintze, of the University of Utah, revealed in a report t o the American Institute of Mining and Metallurgical Engineers. Prof. Hintze explains with proper technical exactness that the carbon dioxide is contained in the earth as a gas under very high pressure, not as the cold solid. But when it comes t o the surface, mixed with about 10 per cent ail, i t expands so fast upon being released from confinement and gives up so much heat that it freezes both itself and the oil. I n its frozen state engineers would apply this gas, the same that is exhaled from human lungs, t o the refrigeration and preservation of food.-Science Semi=
