“Provided:
“1. That the explosive is in all respects similar to the sample submitted by the manufacturer for test.
“2. That double-strength detonators 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 in a frozen condition, 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 the permissible explosives that have passed these tests prior to May 15, 1909. The announcement of the passing of like tests by other explosives will be made public immediately after the completion of the tests for such explosives.
“A description of the method followed in making these and the many additional tests to which each explosive is subjected, together with the full data obtained in each case, will be published by the Survey at an early date.
“NOTES AND SUGGESTIONS.
“It may be wise to point out in this connection 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, also the rate of explosion is slower.