VOL.7, NO. 2
PROBLEM OF PROBLEMS I N CHEMISTRY
357
(6). What weight of KC103 is required to produce 12 grams of oxygen? From the percentage composition of KC1O8,
(1) 100 g. KCIOs = 39.2 g. O1 (2) X g. KClOs 12 g. 0,
(3) 1OO:X :: 39.2:12 (4) 39.2X = 1200
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X = 30.6 g.
(d). What volume of hydrogen can be prepared by the reaction of 10 grams of zinc with hydrochloric a d d ? What weight of hydrogen? ZnCL Hz, From the equation, Zn 2HC1-
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(1) 65.37 g. Zn = 22.4 liters (2 g.) of HP (3) 65.37:10 ::22.4:X(2:Y) (2) 10 g. Zn X liters (Y g.) of HI (4) 65.371 = 224 65.37Y = 20 X = 3.43 liters Y = 0.306 g.
(e). How many cubic centimeters of N / 4 HC1 will juit react with 10 grams of NaHC03? From the equation, HC1 NaHC03 --+NaCl Hz0 CO,,
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1000 cc. N/4 HCl 84/4 or 21 g. NaHCOi (2) X cc. N/4 HCI 10 g. N ~ H C O I X = 476 cc. (1)
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(3) 1000:X :: 21:lO (4) 21X = 10,000
The number of examples that might be given is unlimited. The chief advantage that I can see in this method is the uniformity of procedure, whether the problem deals in grams, mols, volumes, or normalities, so that the inexperienced student can always know how to start. I have tried the plan with good success in my classes, and 1 would welcome any criticisms or suggestions from any readers of THIS JOURNAL,^^^ how to simplify further one of the hardest spots in teaching chemistry in high schools.
Turquoise Mined in Prehistoric California. Extensive mining operations were carried on near Victoriville, California, many centuries ago, M. J. Rogers, who has'recently completed a study of the mines in the Mohave Sink area for the San Diego museum, has discovered. There are indications of over two hundred mines in this region which Mr. Rogers believes were abandoned many centuries ago. The material mined was the semiprecious stone turquoise, which was so extensively used in prehistoric times hy the Indians in Arizona, New Mexico, Mexico, Yucatan, Peru, and Chile, where it was employed in mosaic inlay. The shields and masks from prehistoric times in Mexico are the finest examples of inlay mosaics known from the western hemisphere. The prehistoric mines were all of the open-pit type excavated through solid rock, by primitive stone tools still found near the mines, to a depth of six or eight feet. During the centuries since the mines were abandoned the pits have filled with loose rock and sand, thus preserving these ancient workings from destruction. There is evidence to show that the early Pueblans from eastern areas operated the mines, and it seems probable that they were abandoned because of the distance from water, which today is only to he had during part of the year a t a distance of several miles.-Science Service
