124 CURRENT TOPICS.

mixing of the ingredients, separation by gravi ty during solidifiea tion, or segregation in the mould; (4) excessively coarse struc- ture, due to casting at too high a temperature; (5) defects due to wrong thermal treatment, such as quenching frmn a high tem- perature, heating at too high a temperature or for too long a t ime during annealing, " b u r n i n g " in the case of alloys of copper and zinc, or unequal thermal treatment of different parts of the same casting or forging; (6) defects due to molecular change other than that produced by mechanical stress; (7) shrinkage cracks; (8) defects due to molecular change produced by mechan- ical deformation, viz., brittleness of cold-worked metals, chilling cracks, and cracking during hot working; (9) corrosion; (IO) erosion.

Gas Evolution and Capacity of the Lead Accumulator. F. STRE1NTZ. (Zc~t. Elektrochem., xvi, 747 . ) - -A complete investiga- tion of the gas evolution (compared with a copper voltameter) and of the changes in potential of the electrodes in an accumulator lends to the conclusion that hydrogen may be occluded by the reduced negative plate in charging. Oxygen absorption also takes place in the positive plate, but this is due to its penetration to the metal and formation of more peroxide. The discharge data show that the sharp fall in potential may be due to the exhaustion of the negative or of the positive plate. The former is the more usual case in actual practice, but the latter may occur either ( I ) in an initial discharge when the positive plate is not completely formed; or (2) when the charging has been so carried out that the negative plate has been enabled to occlude considerable quantities of hydro- gen. In the latter of these cases the capacity of the cell is of course foumt to be higher than usual.

Spark ing at the Electrodes. A. KAILAi;. (Zeit. anorg. Chemic., lxvili, I 4 I . ) - - T h e anodic disturbances which are observed occasionally in the electrolysis of fused lithium chloride and other salts have been investigated. Tbe author does not support the view that the phenomenon is caused by the formation of a sub-chloride in the melt, or by the appearance of a film of silicic acid ( f rom the vessel) on the cathode. The electrolysis proceeds normally with a higher temperature and he suggests that the cause is a change in the viscosity of the melt. This view is supported by the fact that under sbnilar conditions the critical temperature is ioo ° higher for pure lithinm chloride than for a 50 per cent. mixture of lithium and potassium chlorides. The sparking is produced quite readily with a platinum (instead of a carbon) anode, while there is no disturbance at all with an alternating current. While the sparking lasts it is noticed that the apparent r isistance of the cell decreases with increasing e.m.f. A mixture of I part lithium bromide with 6 parts lithium chloride does not spark nearly so

CURRENT TOPiCs. ~25

easily as pure chloride nor as a mixture of lithium and potassium chlorides. Oscillographic reproduction of the curve of current strength during the disturbance shows that when the anode is sufficiently deeply immersed, there are no great fluctuations with an e.m.fi of I I o volts and a resistance of 19 ohms. From these facts the author prefers a purely physical explanation o,f tl:¢ phenomenon.

Cold Vulcanizat ion. H. E. POTYS. (Zeit. chem. Ind. Koll., vii, I I I . ) - - B y s o w ' s explanation of the adsorption of sulphur- chloride by rubber is insufficient. Bysow measured the surface tension air-solution. The determining factor in adsorption on Gibbs' theory, is the variation in the tension rubber solution. This latter is unknown. In an editorial note W. Ostwald agrees, but suggests the two tensions may run in parallel series. He notes that Traube 's theory of attraction pressures is open to the same objection.

Electric Steel Refining. D. F. CAMPBELL. (Iron c~nd Steel Inst., Sept., I9Io . ) - -Descr ibes the great possibilities of electrical refining in conjunction with the various steel processes. The in- crease in the capacity of the Talbot and other open-hearth furnaces is very important, because the expensive processes of desulphuriza- tion and attaining a teeming heat can be most profitably carried out by t ransferr ing a portion of the charge to the electric furnace and making up again in the main furnace with raw material. I t will be cheaper to add an electric furnace to a Bessemer plant than to replace it by open-hearth furnaces. The following are the most desirable features of design: I. The best open-hearth design, with homogeneous solid bottom and bands free from im- bedded electrodes. 2. All electrical mechanism, generators, trans- formers, etc., should be separate from the furnace. 3- Maintain a high power factor. 4- ,The roof should be protected f rom direct radiation by the electrodes and the intensely heated area of slag should be as large as possible. 5. The heat should be applied to the slag, which must be kept very fluid and hotter than the steel.

T h e Qual i ty of Boiler Tubes . (Iron Age, lxxxvi, I 6 . ) - - A t the Convention of the American Boiler Manufacturers ' Association, Mr. Charles S. t~lake, Secretary of the Har t ford Steam Boiler In- spection and Insurance Co., attacked the quality of boiler tubes. He stated that " tube failures are woefully common. Twenty-five years ago the average steam pressure ran f rom 80 to ioo lbs., and the tubes in use at that time were identical in thickness, except in specific instances, with those in use to-day for pressures of I5o lbs. to i75 lbs., and the average quality has not improved, so that the standard commercial tube of to-day is no better than, if as good, as the tube of . those 'days ."