ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 135 



ammonium chloride solution added and allowed to remain until all the 

 chromate has become converted to chloride. The completion of this 

 reaction is marked by the disappearance of the characteristic red 

 coloration of silver chromate. The surplus liquid is now dried off with 

 cigarette paper, and the excess of silver chloride removed by sodium 

 thiosulphate solution. After thorough washing, the preparation is either 

 mounted in glycerin, or, after dehydration by absolute alcohol, in Canada 

 balsam. The staining is uniform throughout, the colour is yellow, and 

 the outline of the mucilage is quite sharply marked off. 



Mucilaginous plants, Batrachospermum, Mivularia, &c, may be 

 coloured by first impregnating with bichromate and then treating suc- 

 cessively with silver nitrate and sodium chloride solutions. The appli- 

 cation of this process to seaweeds indicates a method of determining 

 the distribution and the chemical nature of salts present in the tissues 

 of these plants. 



Convenient Staining Dish.* — Mr. J. H. Schaffher has designed a 

 staining vessel (figs. 31, 35) which combines the advantages of tho 

 Stender dish and the staining dish made by placing a number of crystal- 

 lising dishes inside each other. It is made of white glass 2 mm. thick. 

 The inside height is 80 mm., of the central part 60 mm. ; the interna) 

 diameter 80 mm. ; diameter of central column, 68 mm. The cove- 

 should be 6 mm. thick around the edge, which is grooved so as to fit 

 accurately to the top. The dish will hold eight or ten slides at a time. 



(5) Mounting, including- Slides, Preservative Fluids, &c. 



Apparatus for Removing Air-bubbles from Mounts.t — Mr. J. H. 

 Cooke describes an exhaust apparatus for removing bubbles from mounts 

 (fig. 36). It consists of a slip of plate glass 4 in. by 11 in., to which is 

 cemented a wooden frame of such a size as to allow ordinary slides to be 

 placed in it. In one side of the frame is bored a hole, and into this is 

 cemented one end of a rubber tube, 6 in. long and 3/16 in. in diameter. 

 A piece of glass tubing B, 1 in. long, closed at one end, and having a 

 small hole at about a quarter of an inch from the closed end, is inserted 



Fig. 36. 



in the free end of the rubber tube, and so arranged that the hole shall 

 just be covered by the rubber, and the closed end outwards. To use the 

 apparatus, the mount is placed in the cell and covered with a second 

 piece of glass of the same size as the first, and the edges of which have 

 been greased with tallow. If the frame have been properly made the 

 cell will now be air-tight. Exhaust the cell by drawing air through 

 the tube. The valve formed by the hole will prevent the re-entrance 

 of air, and any air-bubbles in the mount will quickly disappear. 



* Journ. App.'Micr., ii. (1899) p. 559 (2 figs.). t Tom. cit., pp. 621-2 (1 fig.). 



