PRESERVATION. 



[ 634 ] 



PRESERVATION. 



that the heated cement used to fasten the 

 ring to the slide must accurately coat every 

 portion of the two surfaces in apposition, 

 and that the surfaces to which the liquid 

 cement is applied must be perfectly clean 

 and dry, so that the cement may come into 

 contact with the surfaces of the glass. 

 Rings of India-rubber and gutta-percha are 

 very useful instead of glass. 



When the objects are very large, the 

 rings may be conveniently replaced by cells 

 constructed of slips of glass, arranged so as 

 to constitute four sides of a box, the bottom 

 of the box being formed by the slide, and 

 the top by a plate of thin glass : the pieces 

 should be cemented together by marine 

 glue. 



Smaller cells may be made with marine 

 glue, melted, dropped upon a slide and flat- 

 tened whilst warm with a piece of wetted 

 glass, the superfluous portions and central 

 portion cut away with a knife. Should the 

 marine glue become loosened from the slide, 

 it may be re-fastened by heat ; and if the 

 upper surface be not perfectly flat, it may 

 be made so by grinding with emery-powder 

 and water upon a plate of metal or upon a 

 stone. 



Minute objects may be mounted in liquid 

 in a variety 'of ways, the choice of which 

 will vary with their nature. They are 

 generally mounted in shallow cells, the 

 sides of which are formed by varnish. 



The old method consisted in placing 

 the object upon a slide, adding a drop or 

 two of the preservative liquid, applying the 

 glass cover, adding more of the liquid, or 

 removing excess with blotting-paper, until 

 the space between the slide and cover was 

 accurately filled, then applying to the mar- 

 gin of the cover and the adjacent portions 

 of the slide a coat of some liquid cement, as 

 gold-size, asphalt solution, black japan, &c. 

 Objects thus mounted keep well for a time; 

 but the cement soon apparently runs into 

 the space between the cover and the slide, 

 and the object becomes spoiled. It is often 

 requisite, however, to mount an object in 

 this way, which may be lying upon a slide, 

 perhaps in some peculiar position which it 

 is important for it to retain ; when this is 

 the case, the electrical cement with balsam 

 and tallow should be used; and there is less 

 fear of change, provided spirit be not used 

 as the preservative liquid. 



Whenever it is possible, then, a cell- wall 

 should be previously formed, by laying a 

 ring or square of one of the liquid cements 



upon the slide with a camel's-hair pencil, 

 and applying a continued heat until it be- 

 comes thoroughly hard when cold. The 

 cements generally used aro : asphalt solu- 

 tion ; gold size with which a little finely 

 powdered litharge has been well mixea, 

 immediately applied, as it soon hardens ; 

 sealing-wax varnish ; solution of marine 

 glue in naphtha, or of Canada balsam in 

 benzole or chloroform, or the balsam alone. 

 Allport's liquid marine glue is very useful. 

 If the upper surfaces of the rings or squares 

 formed of these compounds, when thoroughly 

 dry and hard, be not perfectly flat, they 

 may be made so by grinding alone, or with 

 emery and water, upon a piece of metal, 

 marble, or a stone. The object is then 

 placed in the cell, the preservative liquid 

 added, and the cell closed as above de- 

 scribed. 



The following are the most important 

 preservative liquids and compounds : 



Thwaites's liquid is thus prepared : to 

 16 parts of distilled water add 1 part of 

 rectified spirit, and a few drops of creosote 

 sufficient to saturate it; stir-in a small quan- 

 tity of prepared chalk, and then filter. With 

 this liquid mix an equal measure of camphor- 

 water, and before using, strain through fine 

 muslin. Used for preserving freshwater 

 Algae, as having but little action upon the 

 endochrome. 



Haifa's liquid. Prepared with bay-salt 

 and alum, of each a grain, distilled water 

 1 oz. ; dissolve. Forms a readily prepared 

 substitute for the former in the preservation 

 of the Algae (Desmidiacese). 



Hantzsch, quoted by Carpenter, produced 

 a fine preservative medium for minute 

 A.lgae ; composed of 3 parts of alcohol, 2 of 

 distilled water, and 1 of glycerine ; and the 

 object, laid in a cement-cell, is covered with 

 a drop, and placed under a bell-glass. Al- 

 cohol and water evaporate, and leave the 

 glycerine: more is added time after time, 

 and the cell is thus filled. 



Acetate of alumina. 1 part of the salt to 

 4 parts of distilled water. Topping finds 

 this the best preservative for delicate vege- 

 table colours. 



Distilled water. Very often usd for 

 preserving Algae ; but perhaps camphor- 

 water would be better. 



Camphor-water is prepared by digesting 

 distilled water with a lump of camphor. 



Spirit and water. Proof-spirit is prepared 

 by mixing 5 measures of rectified spirit 

 with 3 of distilled water. It is frequently 



