ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 115 



ment of acetic acid instead of acetic anhydride in its preparation. He 

 gives the exact mode of making up the reagent, as follows. Two separate 

 solutions are prepared. (1) -4 p.c. of nitric acid in acetic anhydride ; 

 (2) A mixtiire in equal parts of the three alcohols, methyl, ethyl, and 

 iso-amyl. Immediately before use, 1 part of (1) is added to ;-> parts 

 of (2). 



The Brinell Method of Hardness Measurement at the Brussels 

 Congress.* — The papers read at Brussels on this method of testing, now 

 assuming considerable importance, are summarised by H. le Chatelier : 

 (1) Influence of variation in diameter of ball, and in pressure. If H is 

 the hardness number obtained under tlie standard conditions (ball 

 10 mm. diameter, pressure ;3000 kg.), H dp the hardness number given 

 with ball diameter d and pressure p, then— 



H = H^^^ 



d 20,000 



10 17,000+1? 



(2) Degree of accuracy obtainable — the error should not exceed 0-5 

 p.c. ; (8) Relation between hardness number and maximum tensile 

 stress. This important point is fully considered. For nearly all classes 

 of steel the tenacity may be calculated within 5 p.c. by multiplying the 

 hardness number by a coefficient depending on the kind of steel. The 

 coefficients given by different workers and for different material vary 

 from 0*344 to 0'376 ; (4) Hardness tests by impact, and the possibility 

 of substituting hardness for tensile tests, are considered. 



Alloys of Zinc and Iron.t — S. Wologdine prepared alloys con- 

 taining up to D'T) p.c. iron by dissolving iron in molten zinc. By 

 heating an alloy containing 8*5 p.c. iron at 1000° C, a residue with 

 42 p.c. iron was obtained. The etching reagents giving the best results 

 for microscopic examination were a 5 p.c. solution of iodine in absolute 

 alcohol, and a lead chloride solution. With 0*07 p.c. iron well marked 

 crystals of a hard constituent were detected. With 8 p.c. iron the alloy 

 consisted wholly of this crystalline constituent. By dissolving out the 

 excess of zinc in a 7*1 p.c. alloy with lead chloride solution the con- 

 stituent was isolated and found to contain 8- 14 p.c. iron. It appears to 

 be FeZuiQ. A freezing point curve is given for the system for the 

 range to 12 p.c. iron, showing a maximum at 8 p.c. of 750° C. The 

 melting point of zinc appears to be raised by smallest additions of iron. 

 Zinc and the compound FeZuio do not give solid solutions. 



Constitution of Hardened and Tempered Tool Steels. J — E. Heyn 

 and 0. Bauer, investigating the nature of troostite and sorbite, quenched 

 small pieces of a eutectoid steel (carbon 0"9r>p.c.) at 1)00° C. These 

 were then heated at different temperatures and for various lengths of 

 time and again quenched. The hardness of each piece was measured by 

 the Martens sclerometer, and the rate of solution in dilute sulphuric 

 acid determined. The carbon condition was determined by dissolving 

 in 10 p.c. sulphuric acid in absence of air, and estimating carbon , 



* Rev. Metallurgie, iii. (1906) pp. GS'J -700. 



t Tom. cit., pp. 701-8 (7 figs.). 



X Stahl uud Eisen, xxvi. (1906) pp. 778-81, 915-22, 991-7 (19 figs.). 



I 2 



