CURRENT TOPICS. 89

when trees are infected it soon girdles the twigs, branches, and trunks, thus causing their de~th.

At this season of the year, when chestnut trees are found with branches bearing dry leaves and immature burrs, cankers, orange-colored pustules, etc., it is an indication that the tree is seriously diseased.

The bulletin also refers to the economic and profitable utiliza- tion of trees killed by the blight. The Commission acquired much valuable information upon the subject, and can therefore prove of genuine service to those seeking markets for commercial products of the chestnut.

Chestnut nursery stock can only be sold and shipped after it has been carefully inspected and properly tagged. A tree that does not appear to be entirely free from the disease is condemned and: burned.

Copies of the bulletin are available and will be sent without charge upon request to the Commission, Morris Building, Philadelphia.

Chlorides in Feed-water. E. E. BASCH. (Techn. Ru~dschau, xvii, 56I.)---The main source of corrosion in steam boilers is magnesium chloride. The boiler plate becomes overheated under the boiler scale, and the hydrochloric acid is set free and causes corrosion. Sodium chloride is considered harmless until it over- steps the saturating point, and so precipitation occurs. A mixture of lime and soda is successfully used to make magnesimn chloride harmless. Caustic soda can be used also, but is more expensive. The only remedy for an excess of sodium chloride is its removal by distillation, which is too expensive.

The New Hydra Photographic Plate. O. MENTE. (Atelier Phot., xix, 82.)--The gradation of the image is not between the deepest shadow and the highest light, as in ordinary plates, but between the deepest shadow and some one high light, as all higher lights have this same density and no solarization appears. Ex- posures not exceeding forty times normal may be developed with pyro-soda, but a special developer is recommended for exposures beyond this limit. The absence of halation is partly due to the thickness of the film and partly to a red backing, the color of which disappears in the fixing bath.

Explosion of Radium Bromide. B. Josr. (Chem. Zeit., xxxvi, I38.)--Occasional explosions of specimens of radium bromide are attributed to the gradual absorption of moisture, which weakens the forces of cohesion in the crystal to the point where the pressure of the accumulated emanation (helium) suddenly ruptures the crystal.