ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 103 



Method for Distinguishing Sulphides from Oxides in Steel.* — 

 It is shown by G. F. Comstock that light grey inclusions seen in 

 polished unetched sections of steel do not always indicate manganese 

 sulphide, as commonly believed. Iron oxide occasionally presents a 

 similar appearance. In cases of doubt the nature of the inclusions can 

 be definitely determined by the use of boiling alkaline-sodium picrate, 

 the reagent used to darken cementite. This reagent attacks sulphide 

 inclusions, changing the colour from light grey to black, while oxide 

 inclusions are quite unattacked. Numerous photomicrographs are given 

 illustrating the use of the reagent. It is made by dissolving 25 grm. 

 sodium hydroxide in GO-70 c.cm. water, adding 2 grm. picric acid, and 

 heating till the acid is dissolved, when the volume is made up to 

 100 c.cm. with watei'. To etch, the solution is brought to boiling, the 

 specimen immersed, and boiling continued for ten minutes. Then the 

 specimen is removed, washed, and dried. 



Annealing of Bronze.f — An elaborate study has been made by 

 C. H. Mathewson and P. Davidson of the combined effects of time 

 and temperature of annealing and of cold-working with regard to the 

 production of uniform structures and growth of recrystallized grain in 

 bronzes containing 1 to 8 p.c. tin. The time necessary for the removal 

 of the cored structure of the solid solution by diffusion is the same 

 whether the alloys have or have not been cold-worked after casting. 

 A given grain-size produced by annealing after deformation corre- 

 sponds to the same degree of diffusion whatever the combination of 

 time and temperature used in the annealing. Alloys which have been 

 rendered homogeneous by a preliminary annealing develop a coarser 

 grain on subsequent cold-working and annealing than alloys which are 

 similarly treated but receive no preliminary annealing before cold- 

 working. Numerous photomicrographs are shown in support of these 

 conclusions. 



An Unusual Feature in the Microstructure of Wrought-Iron.t— A 



peculiar structure sometimes shown by wrought-irons high in phosphorus 

 is described by H. S. Rawdon. The ferrite crystals present a mottled 

 appearance after prolonged etching with an acid reagent such as 5 p.c. 

 nitric acid in alcohol, which extends in streaks over the surface of the 

 specimen. This intra-crystalline etch-pattern is quite distinct from the 

 etching-pits which result from prolonged etching of ordinary wrought- 

 iron. It is considered to be due to the non-uniform distribution of 

 dissolved phosphorus in the ferrite, the area constituting the mottled 

 etch-pattern being relatively high in phosphorus. By using Stead's 

 cupric chloride reagent the patterns can be more strikingly developed. 

 The fractures in some wrought-iron articles which had failed in use, and 

 which showed these features in their structure, ran parallel to the 



* Trans. Amer. Inst. Mining Engineers, No. 120 (1916) pp. 2103-10 (17 figs.). 

 t Int. Zeitschr. Metallographie, viii. (1916) pp. 181-218 (28 figs.). 

 X Engineering, cv. (1918) pp. 77-9 (18 figs.). 



