ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 525 



Specific Heat of Iron-carbon Alloys.* — P. Oberhoffer and A. 

 Meuthen have introduced some important improvements into tbe apparatus 

 previously described.! A repeat determination gave a somewbat lower 

 value for tbe specific beat from 0°-650° C. of tbe nearly pure iron used ; 

 tins causes the bend in tbe curve at 650° C. to be sharper. The mean 

 specific beat of iron between and 650° C. is raised by about 0*0011 

 by the addition of • 5 p.c. carbon. The increase in specific heat is pro- 

 portional to the percentage of carbon. Tbe mean specific beat of pure 

 iron is 0-1432 ; that of carbide of iron 0*1581, between and 650° C. 



Use of the Differential Galvanometer.! — A. Portevin contributes 

 some notes on the double galvanometer, and its use in taking heating 

 and cooling curves. By theoretical reasoning be arrives at the conclu- 

 sion that, if certain conditions be fulfilled, the amount of heat liberated 

 is proportional to the horizontal distance of the point of the curve 

 (showing difference of temperature) corresponding to the end of the 

 liberation of heat, from the continuation of tbe part of the curve cor- 

 responding to the absence of critical points. A method of increasing 

 gradually the current supplied to an electric furnace by increasing 

 automatically the cross-section of a Hquid resistance, is described. 

 Great uniformity of beating may thus be obtained. A convenient 

 method of standardising the pyrometer is given. 



Influence of Nitrogen on Steel.§— A. Grabe states that Braune's 

 method of estimating nitrogen gives too high results, due to the 

 presence of nitrite in the potash. Estimations made by the author 

 gave the following figures : — 



1 2 Swedish bar irons • 0020-0 ■ 0045 



38 steels (miscellaneous) ... 0*0025-0*0125 



20 cast irons (miscellaneous) ... 0' 0010-0 '0065 



The author is of opinion that the minute percentages found in 

 wrought and cast iron cannot have the least influence on quality. It is 

 doubtful if percentages less than 0*015 in steel can have a harmful 

 effect. 



Phosphoric Steels. ||— J. de Kryloff has studied more than 250 

 samples of steel which have failed in use. The steels which contained 

 much phosphorus showed a marked inequality in tbe distribution of 

 carbon. Low carbon areas, constituted chiefly of ferrite grains high in 

 phosphorus, were seen in the micro-sections. The author concludes 

 that when tbe percentage of phosphorus does not exceed 0*07, a uniform 

 structure may be obtained by suitable beat treatment ; but when more 

 phosphorus is present, the initial heterogeneity persists after heat treat- 

 ment. 



* Metallurgie, v. (1908) pp. 173-7 (3 figs.). 



+ See this Journal, 1907, p. 757. 



X Rev. de Metallurgie, v. (1908) pp. 295-305 (9 figs.). 



§ Tom. cit., pp. 353-4. || Tom. cit., pp. 355-60 (19 figs.). 



