PREPARATION OF UNKNOWNS IN QUALITATIVE ANALYSIS* J. L. McKEE Royal Military College of Canada, Kingston, Ontario
ONE OF the problems in arranging laboratory work in qualitative analysis is to make each student's assignment of work of equal d3Eculty. This cannot be done for a single set of unknowns, limited to the ions of two or three groups, but a series of sets can be selected of approximately equal diiculty. The illustration shows a section of a chart used for this purpose a t the Royal Military College. Sets are indicated by letters, series of sets by Arabic numerals, and groups of cations by Roman numerals. Each student works through a set having the same nurnber-Al, B1, C1, etc. USE OF THE CHART
Bottles for each student are labeled and arranged in a straight row. All the bottles to contain the first ion are then drawn to the front, and 10 cc. of the solution of this ion is measured into them. They are then returned to their places and the bottles to contain the second ion are treated in the same way. When the set is completed each bottle should contain the same volume of solution. Any error in ming is thus easily detected when the last ion is added. If it is desired to give varying amounts of the different ions, the volume of each solution to be added is marked on the chart, but the total volume for each sample bottle should be the same. This procedure
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Presented at the Section of Chemical Edueation, Canadian Chemical Convention, Toronto, June, 1934.
has been found to be ve@ much quicker than the method of' preparing each unknown separately, and there is much less chance of error. If time permits, it can be arranged that each student gets every ion at least once during the course. C A n O w SOL-ONS
