90 



On the Application of Berlin Black to Microscopic 

 Purposes. By R. T. Lewis. 



(Read March 27th, 1868.; 



In using Brunswick black for object mounting, I haye frequently 

 found cause of complaint against it, on account of its want of 

 opaqueness, its highly reflective surface, the stickiness which 

 sometimes remains for days after it has been applied, and the 

 difficulty of making a thin coating of gum spread evenly upon its 

 surface. I therefore thought it desirable to find, if possible, some 

 substitute which, whilst possessing all its good qualities, should not 

 possess any of its bad ones ; and it occurred to me that Berlin 

 black might meet the requirements of the case. I, therefore, made 

 trial of it, and have found it so well to answer the purpose in every 

 respect, that I have no hesitation in strongly recommending its use 

 to others. When apjDlied to glass, or any other non-absorbent 

 substance, it dries perfectly in the course of a few minutes, with a 

 beautifully smooth, dull surface, upon which thin gum water will 

 spread as easily as upon paper, whilst for all practical purposes, it 

 may be said to be opaque, which properties render it exceedingly 

 useful for spotting the interior of cells in which it is intended to 

 mount objects dry for lieberkuhn illumination. When used for 

 finishing off slides, its blackness is obviously a great improvement 

 upon the treacle-brown of the Brunswick, and if the comparative 

 deadness of its untouched surface should be objected to, a slight 

 amount of rubbing with a soft piece of cloth or silk will produce a 

 polish upon it equal to that of black marble (and it is for this 

 latter quality it is so highly prized by metal workers, who use the 

 Brunswick black for common purposes alone). It is also a very 

 excellent stain for wood, and, as such, is frequently employed in the 

 transmutation of beech into ebony. As regards supply, although 

 it may possibly be new to microscopy, it is an article in every-day 

 use ; but as there are several kinds in the market, it may be as 

 well to state that what is known in the trade as Iles's Berlin Black 

 is greatly to be preferred to any other. This is retailed, in green 

 labelled stone-ware bottles, at Is. and Is. 6d., the smaller size con- 

 taining about one quarter of a pint. 



