------------------------------+------------------------------------- “_Provided:_ “1. That the explosive is in all respects similar to sample submitted by the manufacturer for test. “2. That No. 6 detonators, preferably No. 6 electric detonators (double strength), are used of not less strength than 1 gram charge, consisting by weight of 90 parts of mercury fulminate and 10 parts of potassium chlorate (or its equivalent), except for the explosive ’Masurite M. L. F.,’ for which the detonator shall be of not less strength than 1½ grams charge. “3. That the explosive, if frozen, shall be thoroughly thawed in a safe and suitable manner before use. “4. That the amount used in practice does not exceed 1½ pounds (680 grams), properly tamped. “The above partial list includes all the permissible explosives that have passed these tests prior to October 1, 1909. The announcement of the passing of like tests by other explosives will be made public immediately after the completion of the tests. “With a view to the wise use of these explosives it may be well in this connection to point out again certain differences between the permissible explosives as a class and the black powders now so generally used in coal mining, as follows: “(_a_) With equal quantities of each, the flame of the black powder is more than three times as long and has a duration three thousand to more than four thousand times that of one of the permissible explosives; the rate of explosion also is slower. “(_b_) The permissible explosives are one and one-fourth to one and three-fourths times as strong and are said, if properly used, to do twice the work of black powder in bringing down coal; hence only half the quantity need be used. “(_c_) With 1 pound of a permissible explosive or 2 pounds of black powder, the quantity of noxious gases given off from a shot averages approximately the same, the quantity from the black powder being less than from some of the permissible explosives and slightly greater than from others. The time elapsing after firing before the miner returns to the working face or fires another shot should not be less for permissible explosives than for black powder. “The use of permissible explosives should be considered as supplemental to and not as a substitute for other safety precautions in mines where gas or inflammable coal dust is present under conditions indicating danger. As stated above, they should be used with strong detonators, and the charge used in practice should not exceed 1½ pounds and in many cases need not exceed 1 pound. “JOSEPH A. HOLMES, “_Expert in Charge Technologic Branch._ “Approved, October 11, 1909. “H. C. RIZER, “_Acting Director._”