ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 145 



The solutions are thus prepared : — A higli 60 c.cm. glass with a 

 wide neck is filled two-thirds full with selected white gum arable (in 

 Ijieces, not powder), and then acetate of potash or ammonia is added, 

 or a solution of chloral-hydrate (of several per cent.) to which 5-10 

 per cent, of glycerine has been added. The gum with frequent 

 shaking dissolves in a few days and forms a syrupy fluid, which is 

 slowly filtered for twenty-four hours. The clear filtered fluid will 

 keep a long time, but if spores of fungi begin to develop a little 

 chloral can be added and the fluid refiltered. 



Preparation of Dammar Varnish.* — C. J. M. says that none of 

 the receipts given in books enable the amateur to prepare a satisfactory 

 article. Dammar is not entirely soluble in ether, benzole, or turpen- 

 tine, at ordinary temperatures. If heat be used, the solution is more 

 complete, but, sooner or later, the product will become milky, and 

 then it will be found impossible to clarify it. 



To obtain a perfectly limpid solution, permanently remaining so, 

 proceed as follows : To 4 drachms of crushed Indian dammar add 

 8 liquid drachms ' of pure benzole, and allow the resin to dissolve at 

 the ordinary temperature. After a day or two, an insoluble residue 

 will be found at the bottom of the vessel. Carefully decant the 

 supernatant clear liquid, and add to it 80 minims (1^ drachm) of 

 spirits of turpentine. The preparation is then complete. The object 

 of adding turpentine is to ensure toughness in the dried film. 

 Without the turpentine the dried film would be brittle. He does not 

 think that any advantage is derived from the addition of mastic to 

 the preparation. 



Hunt's American Cement.t — Mr. J. Ford has received from an 

 American correspondent the following recipe for making the cement, 

 so effectually used by professional mounters, and which has been 

 regarded as a trade secret : — 



" Take some zinc white as sold for painters' use, drain off the oil, 

 and mix with Canada balsam, dissolved very thin with chloroform. If 

 it does not flow freely from the brush, add a little turpentine. The 

 mixture should be about the thickness of cream, and kept in a bottle 

 with a glass cap." 



Mr. F. J. Allen adds : — Having sealed the slide with the cement, 

 paint on it with artists' oil-colours, thinned if necessary with turpen- 

 tine, and when dry varnish it with very dilute balsam to give it a 

 gloss. 



Mayer's Water Bath.J — A convenient form of water bath, devised 

 by Dr. P. Mayer, is shown in fig. 30. 



It is a small brass box, 18 cm. long, 9 cm. wide, and 8 cm. high. 

 The tube A, through which the water is received, and the rod B 

 serve as handles. The receiving tube is closed by a cork provided 

 with a glass tube for the escape of steam, which is bent in the form of 



* Sci.-Gossip, 1882, p. 257. 

 + Journ. Post. Micr. Soc, i. (1882) p. 193. 



t Cf. C. O. Whitman in Amer. Natural., xvi. (1882) p, 785 (1 fig.). 

 Ser. 2.— Vol. III. L 



