2. Average values for the percentage of students having an ion who correctly reported it have been given. From this data, i t is concluded that the results for the determination of magnesium, calcium, zinc, aluminum, chromium, tin, and arsenic are sufficiently below the accuracy of the other ions to warrant further study and work on the procedures and tests for their determination. 3. Average values for the percentage of students incorrectly reporting an ion are given. The results indicate that potassium, sodium, magnesium, iron, and aluminum are incorrectly reported by far too many students, and work should he done to determine and remedy the causes. 4. Procedures for the determination of calcium, cobalt, aluminum, chromium, tin, and arsenic have been modified. These changes have increased the percentage of students correctly reporting the ions. 5 . Changes have been made in the determination of potassium, aluminum, iron, and bismuth ions which seem to have decreased the per cent of students incorrectly reporting the ions. 6. A modification in the method of dissolving CoS and NiS as well as the sulfides of Division A, Group I1 has been suggested which will decrease the amount of acid fumes in the laboratory. 7. A modification of the determination of strontium ion in the presence of calcium ion has been suggested which, i t is believed, will increase the accuracy of the method. The writer wishes to thank his colleagues for their aid in securing data and for their suggestions.
Powdered Rock May Prevent Mine Blasts. Safety methods adopted by U. S. government authorities and the American Engineering Standard Committee would have prevented the recent coal mine disasters in Oklahoma and West Virginia, in the opinion of Dr. Thomas T. Reed, safety service director of the U. S. Bureau of Mines. "The actual cause of the two blasts has not yet been determined," Dr. Reed said, "but they could not have happened if safety rules had been strictly followed. Gas and coal dust need not be allowed t o accumulate and sp&ks and flame to set them off can be kept out of coal mines. A new method of preventing coal dust explosions by means of spraying uninflammable rock dust wherever the inflammable coal dust collects, would have stopped the explosion from traveling through the mine air. "A mine explosion is somewhat like a gun firing," Dr. Reed added. "A flame or spark sets off the collected gas which acts like the hammer in a gun, and the exploding gas sets up clouds of dust. If the dust is of comparatively pure coal it will explode and the flame will spread through the mine air as far as the dust extends. Powdered rock sprayed about acts as a damper." According to the American Engineering Standards Committee, about two-thirds of the fatal and serious accidents in bituminous mines could he prevented. During 1924, officials of the committee said, only one company in America practiced rock dusting on any large scale. At present, however, over 200 mines are rock dusted, but this is only about 4 per cent of all the soft coal mines in the United States.-Science Sem'cc
