346 SUMMARY OF CURRENT RESEARCHES RELATING TO 



lutely certain method of distinguishing between butter and some of its 

 substitutes, and that of all methods proposed, the microscopic are perhaps 

 the least reliable. 



Microscopic Structure of an Armour-plate.* — Dr. H. Wedding de- 

 scribes the microscoi)ical examination of a compound arn?our-plate, from 

 which it appears that the different varieties of iron and steel used in the 

 construction of such a plate cau be recognized without difficulty by means 

 of the Microscope. The plate examined, which was one of the largest used 

 (300 mm. thick) consisted of a base composed of a series of hammered plates 

 of puddled iron 35 mm. in thickness, welded together into a plate of 215 mm. 

 thickness ; a face of cast iron (containing 0"4:5 per cent, of carbon) rolled 

 into a plate 15 mm. thick; and an intermediate layer of steel which had 

 been run in between these two plates and allowed to solidify ; the whole 

 being finally rolled at a red heat. 



A transverse section was polished, cleaned with water, alcohol, and 

 ether, etched with a weak solution of hydrochloric acid (one drop of acid 

 in a litre of water), cleaned a second time, and then tempered to a yellow 

 tint, when the etched figures stood out in orange upon a yellow ground. 



The section was then submitted to microscopical examination and the 

 following features were observed. The surface-plate displays the charac- 

 teristics of cast iron poor in carbon, namely homogeneous iron with uniform 

 inclusions of angular flakes and crystals of iron ; in the steel plate the 

 homogeneous iron is reduced to a network enclosing large masses of 

 crystallized iron and small pores ; while the base-plate is characterized by 

 welding joints in the form of pores permeating stringy iron in which the 

 crystalline structure is developed parallel with the joints. The quantity 

 of crystals present may be regarded as an indication of the percentage of 

 carbon, and they are seen to diminish in number where the otherwise homo- 

 geneous iron of the surface-plate comes into contact with the steel. Other 

 changes of character observed near the point of contact of the different 

 materials are detailed by the author and suggest that the Microscope may 

 perhaps be used not only to determine the nature of the metal, but also to 

 estimate its homogeneity, purity, &c. 



Microscopist's Working Table.j — In a series of articles on "The 

 Naturalist's Laboratory " by an anonymous writer, a microscopist's working 

 table is thus described : — '• As a very large part of the naturalist's work 

 nowadays calls into use that most useful of modern inventions, the compound 

 Microscope, a special table designed to facilitate research must here be 

 looked upon as something indispensable. The objects of the design, now 

 submitted to the notice of students of nature for the first time, are to 

 afford general convenience during study, and to enable one to record 

 observations graphically on the sjiot. To accomplish these the table is 

 divided into two parts, the microscopist's, M (figs. 93 and 94), and the 

 artist's portion, D. The dimensions of the table are clearly indicated on 

 the figures. Fig. 93 is a working plan to show the end elevation of the 

 structure ; fig. 94 gives a good idea of the shape of the table-top. Each 

 part is furnished with two drawers as shown in fig. 93 ; the drawers under 

 D afford space for the storage of colour-boxes, pencils, paper, &c. ; those 

 beneath M are intended to receive microscoj)ical accessories, such as glass 

 slips, instruments, live-boxes, troughs, and the hundred and one odds and 

 ends that may bj required from time to time by the worker in Nature's 

 unseen universe. 



* Verh. Ver. zur Bcf. d. Gewerbfleisses, 1886, p. 293. Cf. Naturforscher, xx. (1887) 

 pp. 18-9. t Knowledge, x. (1887) pp. 80-1 (2 figs.). 



