PRESERVATION. 



[ 532 ] 



PRESERVATION. 



paper larger than the cover, with a portion 

 cut from the middle larger than the object, 

 is then covered with paste, and a minute or 

 tw^o allowed to elapse, that the paper may 

 become thoroughly imbued with it, the su- 

 perfluous paste being removed with the paste- 

 brush ; the paper with the pasted side down- 

 wards is then laid upon the cover and the 

 adjacent portions of the slide, and gently 

 pressed with a cloth, that it may be accu- 

 ratety applied to the glass surfaces. The 

 whole is then allow ed to dry. The principal 

 point in this process is the complete removal 

 of the superfluous paste before the paper is 

 apphed. If this be not eff'ected, it will be 

 drawn by capillary attraction between the 

 cover and the slide, and reaching the object, 

 will spoil it. 



4. A very secm'e method of mounting dry 

 objects which are not altered by heat, con- 

 sists in laying a ring or square of black japan 

 upon a slide, the thickness of the layer being 

 adapted to that of the object, and applying 

 a pretty strong or long-continued heat until 

 the cement becomes perfectly hard when 

 cold. The object is next placed wdthin the 

 ring, a cover laid on, and heat applied until 

 the cement becomes liquid. Gentle pressure 

 then brings the cement and the margins of 

 the cover into contact; and when the cement 

 becomes cold, the cover is firmly fixed to 

 the slide. 



5. Another method of fastening the cover 

 to the slide is by the use of electrical cement 

 and balsam (Cements, p. 125, 5 b) mixed 

 with 1 or 2 parts of tallow. 



6. Many dry objects can be well preserved 



Mounting in Canada Balsam. — When this 

 is to be done, care must be taken that they 

 are thoroughly dry, otherwise they will ac- 

 quire a milky appearance from being sur- 

 rounded by minute drops of w ater. Some 

 objects in drying curl up or become deformed, 

 although their minute structure may not be 

 essentially changed ; this may be prevented 

 by confining them between two slides tied 

 together with thread, or held together by 

 india-rubber rings, sealing-wax applied at the 

 two ends, or by a folded strip of brass with 

 the ends riveted. If the objects be of tole- 

 rable size, they are then soaked in oil of 

 turpentine kept in an ointment-pot covered 

 with a lid, for some hours, or even days, 

 until the air is entirely displaced from them 

 by the tvu'pentine. The latter will often also 

 remove the colouring matter from some ob- 

 jects, as parts of insects, which may or may 



not be desirable ; hence the duration of the 

 process must vary accordingly. A clean slide 

 is then warmed over the flame of a spirit- 

 lamp, or upon a stove, and some clear bal- 

 sam placed in the middle of it, and rendered 

 more liquid by further gentle heat ; the ob- 

 ject is then carefully removed from the tur- 

 pentine with forceps, drained, and laid upon 

 the warm balsam. Some more balsam is 

 then allow ed to fall from the warmed wire 

 (Balsam) upon the object, and when this is 

 well covered with it, a warmed cover is gently 

 laid upon its sm-face. The superfluous bal- 

 sam then escapes at the sides of the cover, 

 and this should be aided by gentle pressure. 

 The slide is next maintamed at a gentle heat 

 upon a warm mantelpiece, or a piece of tin- 

 plate (Intr. p. xxiv.), until, when allowed to 

 cool, the balsam is perfectly hard. As soon 

 as this is the case, the superfluous portions 

 are cut away or scraped off" with a knife, the 

 sm-faces of the glasses cleaned from any 

 residue by a cloth w etted with oil of turpen- 

 tine, and some sealing-w^ax varnish applied 

 to the edges of the cover and the adjacent 

 portions of the slide. 



7. The success of the operation depends 

 mainly upon two circumstances, viz. the 

 object having been tlioroughly dried, and 

 the exclusion of air-bubbles. The former 

 constitutes no difficulty, time being all that 

 is required ; but the latter requires that the 

 object shall previously have been thoroughly 

 moistened with the turpentine, and that the 

 balsam shall have been added to the object, 

 when laid in the balsam upon the slide, be- 

 fore so much of the turpentine has evapo- 

 rated as will allow air to enter any minute 

 cavities in the object. The heat applied 

 should also be gentle; and if the direct flame 

 of a spirit-lamp be used, its application 

 should be made rather to some portion of 

 the slide near that upon which the object is 

 jDlaced, than directly beneath the object. If 

 much heat be applied, bubbles of the vapour 

 of the turpentine will disfigure the object ; 

 but these will mostly vanish if the object be 

 kept for some time at a gentle heat. 



If air-bubbles have found their way into 

 the object, the slide must be macerated in 

 oil of turpentine until the balsam is dissolved 

 and the object liberated, and a fresh mount- 

 ing made. 



8. If the object be large, it must be 

 mounted in a cell. A glass ring (sold in the 

 shops) of suitable thickness must first be 

 cemented to the slide by balsam; more bal- 

 sam is then added until the cavity is filled. 



