ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 171 



case to correspond with that of the index. Tliese are held in place by 

 suitable supports, and a small air space is left beneath the sealed cover 

 to care for expansion. Entire arms and legs are put up by this process, 

 the far side being as distinct as the near one. The arterial and venous 

 are differentiated by injection of red and blue fluids of appropriate 

 refraction index. 



In 1910 0. W. Wentz exhibited before the Society two small 

 animals and a bone in which the internal structure was exhibited 

 without alteration of the exterior.* In this Journal, 1900, p. 1, there 

 is a paper by H. C. Sorby, F.R.S., on " The Preparation of Marine 

 Worms as Microscopical Objects," the chief intention being to de- 

 monstrate the blood-vessels. 



Metallography, etc. 



Micro-structure of Electro-deposited Copper. f — H. S. Rawdon has 

 studied the micro-structure of copper electrotype plates and its variation 

 with different conditions of deposition. Three types of structure are 

 noted. 1. With low current densities, e.g. 0" 11 amperes per square foot, 

 the crystals are large and well formed except at the surface of the initial 

 deposit, which is finely crystalline. 2. With higher current densities, 

 e.g. • 57 amperes per square foot, the crystals become longer and sections 

 have a columnar appearance under the Microscope. Isolated crystals 

 show twinning. 3. With still higher current densities, e.g. 0"7o amperes 

 per square foot, the structure is much broken up and twinning of 

 crystals very common. These three types of structure are illustrated by 

 photo-micrographs. The crystals are twinned at I'ight angles to the 

 direction of " growth," all the twinned layers being parallel in any one 

 crystal. The twinning of crystals requires the application of force, and 

 it is considered to be brought about by the rotation of crystal units by 

 the side-pressure of neighbouring crystals duilng " growth " of the 

 deposit. These mutual side-pressures must attain a certain value 

 before twinning occurs. In all other cases the metal remains in a state 

 of stress analogous to the condition of a " cold-worked " metal. The 

 mechanical properties of the deposit will therefore be affected by the 

 conditions of deposition. Hardness measurements made on the inner 

 layers (adjacent to kathode) and outer layers of deposits confirmed this 

 view. The inner layer where the crystals are invariably broken up 

 owing to interference during growth is decidedly harder than the outer 

 layer. Further support to this view was obtained by annealing different 

 deposits. Recrystallization upon annealing of copper only occurs if the 

 metal has previously been strained, and is nearly always accompanied by 

 the twinning of crystals. Samples corresponding to the first tyj^e of 

 structure were annealed for two hoars at 210" C. The large crystalline 

 parts of the deposit showed no appreciable change in crystal size or 

 arrangement. The initial thin layer of fine^ crystals had, however, 



* See this Journal, 1910, pp. 395, 397. 



t Met. and Chem. Engineering, xv., No. 7 (1916) pp. 406-8 (7 figs.). 



