Among other investigations conducted in this gallery are those of the effect of sparks on known gas mixtures. These sparks are such as those struck from a pick on flint, but in this case they are produced by rubbing a rapidly revolving emery wheel against a steel file. The effect of a spark produced by a short circuit of known voltage, the flame from an arc lamp, etc., may also be studied in this gallery. STRUCTURAL MATERIALS INVESTIGATIONS. The structural materials investigations are being conducted for the purpose of determining the nature and extent of the materials available for use in the building and construction work of the Government, and how these materials may be used most efficiently. These investigations include: (1).--Inquiries into the distribution and local availability, near each of the building centers in the United States, of such materials as are needed by the Government. (2).--How these materials may be used most efficiently. (3).--Their fire-resisting qualities and strength at different temperatures. (4).--The best and most economic methods of protecting steel by fire-resistant covering. (5).--The most efficient methods of proportioning and mixing the aggregate, locally available, for different purposes. (6).--The character and value of protective coatings, or of various mixes, to prevent deterioration by sea water, alkali, and other destructive agencies. (7).--The kinds and forms of reinforcement for concrete necessary to secure the greatest strength in beams, columns, floor slabs, etc. (8).--Investigation of the clays and of the products of clays needed in Government works, as to their strength, durability, suitability as fire-resisting materials, and the methods of analyzing and testing clay products. (9).--Tests of building stones, and investigations as to their availability near the various building centers throughout the United States.