inspectors in different States are not uniform. Moreover, one State requires inspectors to collect certain information, whereas the requirements of another State are entirely different. Some States do not require a record of injuries or a report to any individual, insurance board, commissioner, or inspector, whereas other States have strictly enforced laws requiring such reports. In addition, the fiscal years of States are not uniform. Unless all States report on the same basis, just comparisons can not be made. It is hoped that during this coming year a bulletin on metal-mine accidents can be prepared, similar to the one on coal-mine accidents above mentioned.

During the year, in addition to the reports on coal-mine accidents, a report on accidents in metal mines, and a report on accidents in quarries, each for the calendar year 1913, were published; also a report on the production of explosives in the United States during 1913 was printed, and a report on the production of explosives during 1914 was submitted for publication. A report on accidents at coke ovens during the calendar years 1913 and 1914 was published, and a report on accidents at ore-dressing and smelting plants for the same years was completed.

The compilation_of_accident statistics is being conducted under the direction of A. H. Fay, mining engineer.

EXAMINATION OF MINING LAWS.

The law examiner continued to collect and examine mining laws and to compile digests of court decisions interpreting these laws, in an effort to indicate to the mining industry or to State legislatures what laws are proving most effective in aiding the development of the mining industry and in the introduction of safer and more efficient methods in mining.

A large report issued in two volumes as a bulletin contains a complete compilation and annotation of all the sections of the United States Revised Statutes and of all acts of Congress relating to mines, mining, mineral lands, and the mineral industry on public lands. The annotation consists of abstracts of court decisions that indicate how the courts have pointed out defects in the statutes, made clear uncertainties, and aided practical application. The large number and wide range of the decisions show that the value of mining laws depends on their status as established by the courts, and the annotations aid a person in determining how to apply the provisions of an act to a mining enterprise.

Two other bulletins containing abstracts of current decisions on mines and mining, covering the periods from December, 1913, to September, 1914, and from October, 1914, to May, 1915, were published during the year.

The law examiner has made considerable progress in preparing a compilation and annotation of State mining laws, a work planned on the same lines as that on the Federal statutes. This work involves the examination of the statutes of all mining States, as well as a careful search in the reports and a study of the decisions in regard to mines and mining rights, and the construction of the State statutes bearing on these subjects.

The work is in charge of J. W. Thompson, law examiner, assisted by U. B. White, law clerk.

EXPERIMENTAL-MINE AND ALLIED INVESTIGATIONS.

The workings of the bureau's small experimental mine near Bruceton, Pa., were extended by lengthening the butt entries and starting two rooms. The entries at the end of the year had a combined total length of about 3,800 feet. During the 7 months given to experimenting, 92 explosion tests were made, a little less than one test for each two working days. About three months' time in the summer of 1914 was spent in repair work, in building new instrument stations, and in lining with concrete the inner 350 feet of the main entries. No testing was done during the last 13 months of the fiscal year 1915, as the technical force was employed in plotting the records of the explosion tests in preparation for a report describing the work of the two preceding years.

The more important results of the year's work may be summarized as follows:

The relative inflammability of the coal dust from coals in five districts, and representing as many types of coal, was determined as a result of 9 to 12 tests. The inflammability of the coals tested increased in the order indicated below, and the degree of inflammability varied, though not directly, with the ratio of volatile combustible to total combustible. The first coal dust on the list was tested the previous fiscal year and found nonexplosive, the second was nonexplosive without the presence of gas, but was explosive in conjunction with 1 per cent or more of fire damp. The list follows:

Wyoming Valley coal---Low-volatile anthracite.
Lykens (special) coal-Higher-volatile anthracite.
Beckley coal_____

-Low-volatile bituminous or semibituminous.
Lower Kittanning coal-Bituminous, but not a true coking coal.
Upper Freeport coal----Bituminous, but not a true coking coal.

Pittsburgh coal----. Bituminous, high-volatile gas and coking coal. In addition to inflammability tests the quantity of incombustible material that, if added to the coal dust, would render the mixture noninflammable was determined for the five coals under two test conditions: First, when the zone of pure or mixed dust under test was placed up to the black-powder shot at the face; second, when a 50foot zone of a pure Pittsburgh coal dust separated the shot from the dust under test to give the effect of a pocket of gas ignited by a blown-out shot. Manifestly, more shale dust was necessary to give the desired protection under the latter test condition than under the former, and the amount of shale dust necessary varied directly with the inflammability of the dust tested. The tests were conducted in the concrete-lined part of the mine to prevent any dust from the roof, ribs, or ballast from entering into the explosion. From the results of the tests recommendations were made to individual operators which, if carried out in the mines working the seams represented, will reduce to a minimum the possibility of a widespread explosion. It is planned to test dusts from other typical coals, including lignites from various parts of the country.

In a large number of tests small percentages of natural gas (less than 1 to more than 3 per cent) were turned into the air current. The presence of this gas increased the explosibility of the coal dust proportionately to the percentage of gas in the air. The gas caused explosions in mixtures of shale and coal dusts, or in coal dusts of low

inflammability, that without the gas would not have supported explosions; also, as a consequence, more shale-dust protection against explosions was required when there was gas in the air current. The amount of additional shale-dust protection required for the different coals for different percentages of gas in the air was determined.

INFLAMMABILITY TESTS.

In connection with these tests rock-dust barriers for stopping explosions were tested. Several of the barriers designed during the preceding year were modified to make them more effective in stopping explosions. Also a new type of barrier was designed, which proved successful in many tests.

In the mine the butt entries were lengthened, two additional rooms started, four additional concrete instrument stations constructed, new instrument cables were laid through pipes in the rib protected by concrete, and the inner 350 feet of the main entries was lined with concrete by means of a concrete gun, to facilitate the cleaning of the mine after explosions and to assure greater accuracy in the results of tests. At the end of the year the experimental mine had explosion passageways about 3,800 feet long and four rooms of an average length of 103 feet each.

A new recording pressure manometer, a new gas-sampling apparatus, an instrument for detecting the direction of air movements, an improved device for registering the velocity of the explosion gases, and new devices for registering the passage of flame were perfected during the year. For demonstration and educational purposes at field meets throughout the country, wooden coal-dust explosion galleries were designed, to be erected temporarily at small cost wherever the mine-rescue meets are held, to demonstrate the explosibility of

coal dust.

TEST OF ROCK DUST IN A COMMERCIAL MINE.

The engineers of the experimental mine, in cooperation with the Pittsburgh Coal Co., began a test to determine the efficiency and cost of rendering coal dust inert by rock dust in a commercial mine. About 2,000 feet of entry in such a mine was dusted with limestone dust during January, 1915, and was inspected every two weeks by one of the bureau's engineers to determine to what extent the rock dust had been contaminated by coal dust and to arrange for further rock dusting if necessary. The results so far seem to indicate that unless much coal is spilled along roadways the method will give better protection against a coal-dust explosion, and, under the conditions tried, might be cheaper than the use of water on a large scale.

REPORTS ON DUST EXPLOSIONS.

Publications of the bureau during the year included a technical paper on "Methods of Preventing and Limiting Explosions in Coal Mines," that discussed methods of treating coal dust so as to keep it from spreading an explosion, and described in detail the rock-dust barriers designed and tested at the experimental mine, prepared by G. S. Rice and L. M. Jones; a miners' circular, outlining what a miner can do to prevent explosions of gas and of coal dust, by G. S. Rice, was also published.

FURTHER TESTS WITH ROCK DUST.

During the coming year it is proposed to make inflammability tests of other coals, particularly those in which the ratio of volatile matter to total combustible is different from that in those already tested, in order to determine whether the inflammability of such coals varies with the ratio mentioned. The tests will be made without any gas in the air current and successively with proportions of 1 to 3 per cent. The efficiency of the rock-dust barriers under various conditions resulting from explosions of different intensities will also be tested, as will the effect of wide places in the starting of an explosion. Mixtures of coal dust with various percentages of water will be made in order to determine how much water is necessary to prevent the starting and extension of coal-dust explosions through wetted dust zones. To obtain the most severe conditions the tests will be made during cold weather.

Plans for the coming year embrace tests with rock dust in a number of mines, in order to determine under operating conditions the efficiency and cost of rock dusting. Coal companies in different parts of the country have expressed a willingness to cooperate with the bureau in such tests.

RESCUE AND FIRST-AID INVESTIGATION AND TRAINING WORK.

The engineers, foreman miners, and first-aid miners of the minerescue cars and rescue stations were engaged chiefly in investigating the causes of mine accidents, in rendering aid at mine disasters, in training miners in the use of first-aid and rescue equipment, in rendering assistance at mine disasters, and in giving first aid to the injured.

During the relatively short period during which the crews of the bureau's cars and stations were able to conduct active training, 60,124 miners visited the cars and stations, 53,612 attended lectures and safety demonstrations, 2,401 received mine-rescue training, and 6,176 were given first-aid instruction.

Details of the instruction, training, and demonstrations in safety methods given from the mine-rescue cars and stations of the bureau are shown in the following tables:

Report of training by mine-rescue cars and stations, July 1, 1914, to June 30, 1915.

Report of training by mine-rescue cars and stations, by months, July 1, 1914, to June 30, 1915, based on certificates issued.

During the year 119 tests of breathing apparatus were made and some miscellaneous tests of inhalation devices and fumigating devices. In the conduct of these tests, 530 air samples were taken; also, 4 air samples were taken in a test of the lungmotor.

During the year 389 tests of safety lamps were made, in which 121 gas samples were taken. Twenty-nine trials were made of a new testing gallery, in which 123 gas samples were taken. A number of experiments and trials were made with portable lamp-testing boxes, in which 74 gas samples were taken.

During the year 83 demonstrations were given, including safetylamp testing, breathing apparatus, and first aid.

ACTIVITIES RELATING TO MINE RESCUE AND FIRST-AID WORK.

Miscellaneous work during the year was as follows:

Schedule 7, "Procedure for Establishing a List of Permissible Miners' Safety Lamps," was drafted for approval by the Secretary of the Interior.

Rescue maneuvers at Terre Haute, Ind., were conducted.

The lungmotor, a mechanical device for resuscitating persons, was investigated and a spirometer was designed.

A new type of oxygen resuscitator was designed.

The manuscript of a miners' circular, entitled "Notes on Miners' Carbide Lamps," was transmitted for publication.

A report on oxygen rescue apparatus; tests and observations, was completed.

A half-hour breathing apparatus was tested for the Navy Department.

RESCUE AND RECOVERY WORK AFTER MINE EXPLOSIONS AND FIRES.

Systematic methods of rescue and recovery work after mine disasters are being improved year by year. The increased efficiency of these methods is due in some measure to the work of men trained