CEMENTS AND VARNISHES 231 



water, melt in the usual way. stir in 3 drops of creosote. It is 

 used warm. 



When the ring of gelatin has become quite set and dry, it may 

 be painted over with a solution of bichromate of potash made 

 by dissolving 10 gr. of the salt in an ounce of water. This should 

 be done in daylight, in order to render the gelatin insoluble. 

 The cover may then be finished with Bell's cement. This process 

 is particularly adapted for glycerin mounts. 



504. The Paper Cell Method. By means of two punches Lee 

 cut out rings of paper of about a millimetre in breadth, and of 

 about a millimetre smaller in diameter than the cover-glass. 

 Moisten the paper ring with mounting fluid, and centre it on the 

 slide. Fill the cell thus formed with mounting fluid ; arrange 

 the object in it ; put the cover on ; fill the annular space between 

 the paper and the margin of the cover with glycerin jefly (a turn- 

 table may be useful for this) ; and as soon as the gelatin has set 

 turn a ring of gold-size on it, and when that is quite dry, varnish 

 with Bell's cement. 



For greater safety, the gelatin may be treated with bichromate, 

 according to Marsh's plan, last §. 



505. Rousselet's Method for Aqueous Mounts {op. cit., § 500). 

 Close the mount with a ring of a mixture of 2 parts of a solution 

 of damar in benzol and 1 part gold-size. When dry, put on three 

 or four thin coats of pure gold-size at intervals of twenty-four 

 hours, and finish with a ring of ^VARD's brown cement. 



506. Miller's Caoutchouc Cement. Composition unknown. 

 May be obtained from the opticians. A very tenacious and 

 quickly drying cement. It may be diluted by a mixture of equal 

 parts of chloroform and strong alcohol (see Rousselet, Journ. 

 Quek. Club, v, ii, 1895, p. 8). 



507. Asphalt Varnish {Bitume de Judee). Unquestionably one 

 of the best of these media, either as a cement or a varnish, provided 

 it he jyrocured of good qualitij. It can be obtained from the opticians. 



508. Brunswick Black. See early editions, or Beale, How to 

 Work, etc.. p. 49. 



509. Gold Size. Best obtained from the oi)ticians. It is 

 soluble in oil of turpentine. A good cement, when of good quality, 

 and very useful for turning cells. 



510. Turpentine, Venice Turpentine (Csokor, Arch. mik. Anat., 

 xxi, 1882, p. 353 ; Parker, Amer. Mon. Mik. Journ., ii, 1881, 

 pp. 229 — 30). Venice turpentine, or common resinous turpentine, 

 evaporated by heat until brittle on cooling. It is used for closing 

 glycerin mounts in the following manner : Square covers are used, 

 and superfluous glycerin is cleaned away from the edges in the 

 usual way. The cement is then put on with a piece of wire bent 

 at right angles ; the short arm of the wire should be just the length 

 of the side of the cover-glass. The wire is heated in a spirit lamp, 



