304 The Microscope. 



Dissolve the dammar in the benzol and filter through absorbent 

 cotton. See that the zinc is perfectly dry, then place a small portion 

 in a mortar, and rub up with the dammar solution. When com- 

 pleted add more zinc, and continue thus till the whole is thoroughly 

 incorporated. Care should be taken that the zinc is rubbed smooth, 

 all lumps remaining after careful trituration being removed. This 

 cement — and, for that matter, all cements — should be kept in closed 

 bottles. When well made this zinc white will prove very serviceable, 

 being hard, durable, and of smooth finish. 



Brunswick Black. 



This is an asphalt varnish, known in commerce as "Brunswick 

 black." It can be used as obtained in the shops. A most satis- 

 factory cement can be made by taking one ounce of the prepared 

 asphalt mass (from which the varnish is made by dissolving in turpen- 

 tine) and dissolving it in a solution of ten grains of caoutchouc in two 

 ounces of benzol. A preparation something like the above the writer 

 has used almost to the exclusion of all others. It makes an elegant 

 appearance, and has shown itself very durable. Frey recommends 

 a French enamel leather- dressing much used by Bourcogne, of Paris, 

 whose mounts are highly esteemed. The writer has never used it. 



Gold-Size. 



This can be obtained from any dealer in painters' goods. The 

 color is not an especially happy one, but it makes a very hard, 

 reliable cement. They who cannot obtain the ready-made article 

 can make it as follows: "Grind together twenty-five parts of strained 

 or filtered linseed oil, one part calcined red ochre, and one part red 

 lead, and boil for three hours. Let stand until the solid matter 

 sinks to the bottom, and decant the clear fluid. Mix the latter with 

 an equal bulk of white lead, boil for an hour, and again let stand 

 and decant." — James^ Elementary Technology 



Besides the cements given above there are a number of others 

 much used, but the writer has found that with Zinc-white, Brunswick 

 black, and Canada balsam, all necessary work can be done. A very 

 delicate sea-green color can be imparted to Canada balsam by add- 

 ing to it a quantity of brass filings. The effect is a very pretty one, 

 and was much used by the late Dr. A. Y. Moore, of Cleveland. Of 

 course, such a preparation should be kept only as a cement, and 

 never used as a mounting medium. 



