470 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Cement Varnishes and Cells.* — Mr. S. G. Shank finds that every 

 medium of an aqueous or glycerin nature sooner or later softens all 

 ordinary cell cements. Mounts of Algag, &c., in copper solution, glycerin, 

 in solution of chloral hydrate, in cells of solution of sealing wax and 

 such similar cements, when about three years old, all show the cement 

 creeping in towards the centre of the mount. All cells to be used for 

 fluid (other than alcoholic) and glycerin solutions should be carefully 

 covered with shellac. This may whiten where the fluid touches it, but 

 it resists well. Cement down the cover with shellac also, and back it 

 with a more tenacious varnish. 



Lovett's cement, which is white lead 2, red lead 2, litharge 3, ground 

 together with thin gold size to a working consistence, hardens more 

 quickly than gold size, and seems to be entirely permanent. Mounts 

 four years old prepared with this cement are still perfect, resisting 

 glycerin and weak alcoholic solutions. This cement is troublesome to 

 prepare and cannot be well kept, like shellac varnish. 



Cells are, as a rule, made too deep or too wide. The expansion and 

 contraction of considerable bodies of fluid soon loosen any but very 

 carefully made cells. Fluid mounts which show signs of failure should, 

 as a rule, be immediately remounted. The presence of air seems to 

 facilitate decomposition. Frequently the bubble is a gaseous result 

 of internal decomposition, which progresses in spite of liberal coats of 

 varnish subsequently applied. 



Glass slips, with concave centre, should be prepared for many objects. 

 They cost about the same as loose glass cells, and are deep enough 

 for a head of Tsenia Solium, &c., and the addition of a ring of thick 

 shellac, well dried, forms a cell deep enough for a wide range of objects. 

 All fluid mounts ought to be revarnished every year whether they show 

 signs of failure or not. 



King's amber or Brown's rubber are transparent varnishes, and 

 neither will impair the beauty of any fancy finish. White and black 

 finishing varnishes may be made by adding to shellac varnish, tube 

 oil-colour, ivory black, or zinc white. The resulting finish does not 

 crack, but is not as brilliant as zinc cement or asphaltum. 



The surface of a slide to which a cell is to be cemented, should be 

 well cleaned with a mixture of equal parts of alcohol and chloroform. 

 The best cement fails to adhere on a dirty glass surface. 



Copal Cement.f — Mr. W. Z. Davies makes a transparent and colour- 

 less cement, which is useful as a finishing varnish and for cell-building, 

 in the following manner : — 



Take best clear copal gum, coarsely pulverized, mix with a sufficient 

 quantity of benzol to cover it, and let stand for 24 hours. Take of 

 chloroform twice as much as of the benzol, and in it as much gum 

 camphor to saturate the chloroform, and then add a small quantity of 

 pale linseed, nut, or poppy oil. The quantity of oil will vary according 

 as a quick or slow drying cement is desired. If no oil, or a very small 

 quantity is added, the cement will dry very quickly. Next add the 

 mixture to the copal and benzol, shaking at intervals for several days, 

 until as large a quantity as possible of the gum has been dissolved. 

 Pour off, filter, and evaporate to any desired consistency. 



This cement adheres well to glass, especially if the glass is warm 



* The Microscope, ix. (1889) pp. 126-7. f T. c, pp. 78-9. 



