ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 375 



particles appeared also to consist of volcanic glass together with felspar 

 crystals, while the small-sized dust was mostly mineral crystals or their 

 disintegrated fragments. Some of the larger particles appeared to be 

 of the nature of a greenish volcanic glass ; there were also crystals or 

 fractured portions of crystals apparently of felspar and quartz. A 

 noticeable feature was the presence of some partially transparent par- 

 ticles of greenish-brown tint which seemed to indicate the presence of 



■ olivine, and sometimes brown coloured semitransparent glassy particles 

 were noticed. Many of the transparent crystals manifested a sharpness 

 on their edges, but others were more or less rounded. When viewed 

 with polarised light, the effect on some of the crystalline particles was 

 very fine. In some of the glassy crystals were noticed numerous internal 

 cavities seemingly enclosing volcanic gases. Some of these particles 

 which did not transmit light appeared to be of the nature of the magnetic 



• oxide of iron. The paper is illustrated by eighteen photomicrographs, 

 thirteen of which give the appearances in the dust from Mont Soufriere, 

 four of the dust from Cotopaxi, and one, that of volcanic iron crystals. 



Analysis of Steel-Works Materials.* — H.Briarleyand F. Ibbotson 

 have produced a valuable work on this subject, and have striven to in- 

 clude only those, methods of analysis which have been verified and tested 

 by the authors themselves or have been done under their supervision. 

 Parts i.-x. (282 pp.) deal with the chemical aspects of analysis, and ■ 

 part xi. with the Micrographic analysis of steel. This latter section, 

 which will naturally be the most interesting part of the book to micro- 

 scopists, deals with the following details :— Preliminary preparations, 

 Methods of polishing, Etching the specimens, Heat-tinting, Rapid 

 method of preparation, Mounting, Microscopic accessories, Photography. 

 The final division, treating of the Microstructure of steel, is subdivided 

 into pure iron-carbon steels, manganiferous steels, and steel castings. 

 There are about fifty photomicrographs embracing a great variety of 

 types of steels, and a copious bibliography. Part xii. deals with pyro- 

 metry, part xiii. with miscellanea. An appendix with a bibliography of 



■ steel-works analysis concludes the work. 



Certain Properties of the Alloys of the Gold-Silver Series.t — 

 W. C. Roberts-Austen and T. K. Rose have found that it is preferable to 

 use only silver as the alloying metal with gold in the manufacture of 

 trial plates. Such an alloy has accordingly been used at the Royal Mint 

 since the beginning of the present year, instead of fine gold, for checks 

 in the assay of standard bars and coins. In view of the minute accuracy 

 with which the operations of coinage have to be conducted, this is a 

 matter of much importance. By this method any errors are avoided 

 which might be caused by accidental variations in weights occurring after 

 the trial plates have been made. 



* Longmans, Green & Co., London, 1902, 501 pp. 

 t Proc. Koy. Soc, lxxi. (1903) pp. 161-3 (3 figs.). 



