96 C. F. ROUSSELET ON SOME MICRO-CEMENTS FOR FLUID CELLS. 



a dislike to varnishes and cements of which the composition is 

 unknown, as, however well they may be spoken of, you are quite 

 in the dark as to their action on mounting fluids. 



" My varnishes are practically two : gold size, — this is composed 

 principally of boiled linseed oil, possibly combined with a resin 

 dissolved in turpentine, in fact a first-rate oil varnish. It should 

 be obtained at a good shop and be of the best quality. My other 

 varnish is shellac, which I always make myself ; it is almost as 

 easy to make as gum-water. Simply place the best shellac you 

 can obtain in a large bottle not more than half or three-quarters 

 full with strong alcohol, shake up frequently until the lac is 

 dissolved ; it is best made at ordinary temperature. The result 

 is a turbid mixture. If you make about half a pint, add a 

 teaspoonful of red lead to the solution and shake it up ; in a few 

 days the red lead will have carried down all the thick matter, 

 leaving a fine clear varnish, which decant. 



" Shellac varnish resists glycerine and its compounds, but has 

 the defect of being brittle, unlike gold size, which retains con- 

 siderable toughness after the lapse of many years. For ringing 

 balsam mounts I add twenty drops of castor oil to 1 oz. shellac 

 varnish, but for other purposes use it pure. 



" The principle of securely closing a cell containing fluid is to 

 use first a varnish not affected by the medium, irrespective of its 

 brittleness, and when the fluid is secure, case with a reliable 

 varnish for security. 



" My practice with glycerine and compounds is this, which will 

 show what I mean. When I have put on the cover I clear away 

 with a fine pipette and suction as much fluid as I can, absorbing 

 the rest carefully with scraps of blotting paper ; I then ring m ith 

 a solution of damar in benzole, a weak and bad varnish, but which 

 has the useful property of sticking to wet glass. When dry I 

 wash under a tap so as to remove all traces of glycerine ; this is 

 important, as no sound joint can be made so long as glycerine or 

 other fluid that persistently adheres to glass is in the way. I 

 then follow with a ring of shellac (pure), when dry wash again 

 and then give two or three coats of shellac, w^ashing if there is 

 any doubt about the joint being perfectly clean. The glycerine is 

 now secure, and the mount is then secured with gold size, which 

 should be laid on thinly and at least six coats. I have never 

 found a slide to leak. If gold size had been used at once the very 



