ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 793 



Baumann sulphur-printing method is commonly used ; bnt Heyn declares 

 that sulphides are not distinguished from phosphides by this method, 

 and recommends the use of silk soaked in a solution of hydrochloric 

 acid and mercuric cloride. The Le Chatelier Microscope is generally 

 employed in works laboratories, while the Martens outfit is more 

 frequently installed in scientific establishments. An arc-lamp, with its 

 carbons set at right angles to each other, by the Diisseldorf firm of 

 Dujardin, is frequently used for photomicrography. The same firm 

 also supplies several types of Microscope stand, polishing apparatus, etc. 

 The Stead workshop Microscope is used in cases where more costly 

 outfits are unsuitable or not considered necessary. Instances of the 

 practical application of metallographies! results and examples of the 

 mode of reporting them are given. Numerous details relating to 

 mechanical testing, pyrometry, and heat-treatment are furnished. 



Testing Steel by Corrosion.* — F. Cloup gives some information 

 about the application of macroscopic etching, which he terms "testing 

 by corrosion," to steel. He has used picric acid as an etching reagent, 

 but recommends a 10 p.c. iodine in potassium iodide solution. A specu- 

 lar polish is unnecessary, but it is advisable to carry the polishing as far 

 as may be practicable. Suitably etched specimens give clear indications 

 of the manner of flow of the metal in the mechanical treatment (forging, 

 stamping, etc.) which it has undergone, and the position and extent of 

 segregation, piping, blowholes, and other defects are revealed. With steel 

 of good quality, free from defects, prolonged etching is necessary to 

 develop the flow-lines. 



Heat-capacity of Metals and Compounds.f — H. Schimpff has deter- 

 mined the heat-capacity of fifteen metals and twenty-nine binary 

 compounds of the metals with each other, for the temperature intervals 

 17° to 100° C, 17° to - 79° C, 17° to - 190° C. The molecular heats 

 of about one-half the compounds are equal to the sum of the atomic 

 heats of the component metals, within 2 p.c, the limit of experimental 

 error. In the remaining cases the deviations from Kopp's law are 

 usually within 4 p.c. Specific heat increases with temperature, but the 

 value of the temperature-coefficient diminishes as the temperature rises, 

 except for bismuth and lead. 



Resistance of Alloys free from Solid Solutions.:}: — K. Lichtenecker 

 has deduced a simple formula for the calculation of the electrical resist- 

 ance of alloys containing no solid solutions. A satisfactory agreement 

 was obtained between observed values and values calculated from this 

 formula. 



Spark Spectra of the Metals. § — C. E. Gissing gives good repro- 

 ductions of photographs of the spark spectra of most of the metals and 

 a few alloys. Containing, in addition, numerous manipulative details, 

 the book should be useful to those who use a prism spectroscope for the 



* Rev. Metallurgie, vii. (1910) pp. 605-11 (9 figs.), 

 t Zeitschr. Phys. Chem., lxxi. (1910) pp. 257-300 (8 figs.). 



% Phys. Zeitschr., x. (1909) pp. 1005-8, through Science Abstracts, xiii. (1910) 

 Section A, p. 150. 



§ London : Bailliere, Tindall and Cox, 21 pp. (50 figs.). 



Dec. 21st, 1010 3 G 



