PRESERVATION. 



[ 633 j 



PRESERVATION. 



to the edges of the cover and the adjacent 

 portions of the slide. 



The success of the operation depends 

 mainly upon two circumstances, viz. the 

 object having been thoroughly 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 uj)on the slide, 

 before 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 i 

 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 

 placed, than directly beneath the object. If 

 much heat be applied, bubbles of the vapour 

 of the turpentine will often disfigure the 

 object for a time; but these will vanish as 

 the object becomes cool. 



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. 



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 balsam is 

 then added until the cavity is filled, the 

 object next added, and the cover applied. 



If the object be minute, its removal for 

 maceration in the turpentine is not requisite, 

 and might entail the loss of the object. It 

 must then be laid upon a slide, a drop or 

 two of turpentine added, and the whole 

 warmed until no air-bubbles are visible. 

 The cover is then removed, most of the tur- 

 pentine drained off, balsam added from the 

 warmed wire, and the cover applied as be- 

 fore : or balsam niav be placed upon the slide 

 near the margin of the applied cover ; and 

 on applying a continued gentle heat it will 

 find its way under the cover, and replace 

 the turpentine as it evaporates. 



If air-bubbles remain in parts of a minute 

 object, a cover should be applied, turpentine 

 added, and the slide held over a lamp until 

 the turpentine boils, and the bubbles dis- 

 appear on cooling. The cover is then re- 

 moved, most of the turpentine allowed to 

 evaporate, the balsam added, and the cover 

 re-applied. Gum dammara may be used 

 in the same manner as Canada balsam. 



Gum and Glycerine. Objects which can- 

 not be conveniently dried may be mounted 

 in a solution of gum-arabic in glycerine ; 

 the manipulations are much the same as 

 with balsam, except that no heat is re- 

 quired. Glycerine jelly is often used. 



Mounting in Liquid. The structure of 

 many objects is so altered by drying that 

 they require to be mounted in some preser- 

 vative liquid. These, if of considerable size, 

 must be mounted in glass cells. 



The cells may consist of glass rings, i. e. 

 portions cut transversely from pieces of glass 

 tubes, of various sizes, according to the 

 dimensions of the objects. In using these, 

 the ring is first warmed in the flame of a 

 spirit-lamp, being held by steel forceps ; one 

 of the ground surfaces of the ring is then 

 covered with marine glue or balsam pre- 

 viously melted in the same flame ; the sur- 

 face of the slide to which the ring is to be 

 cemented is then heated in the flame, and 

 whilst it is hot the surface of the ring coated 

 with the melted cement is applied to it, and 

 the ring pressed firmly, so as to displace 

 the superfluous portions. When cold, these 

 are to be removed with the point of a knife; 

 sometimes a little solution of potash, oil of 

 turpentine, or naphtha is required for this 

 purpose. The cell is then complete, ex- 

 cepting the lid or cover, which consists of 

 a circular plate of thin glass, of slightly less 

 diameter than that of the outer margin 

 of the glass ring. The cell is now to be 

 filled with the preservative liquid, the object 

 placed in it, and the cover applied, being 

 made to slide over the upper surface of the 

 ring, so as to displace any excess of liquid, 

 and prevent the admission of air-bubbles. 

 If the quantity of liquid first put into the 

 cell be not sufficient, more must be added, 

 until slight excess is present; the superfluous 

 portions may be removed by a piece of blot- 

 ting-paper, and the margin of the cover and 

 ring very carefully wiped clean with a silk 

 handkerchief, so that the surfaces may be 

 free from all traces of the preservative liquid. 

 The exposed parts of the upper surface of 

 the glass ring, and the adjacent margins of 

 the cover, are then to be coated lightly with 

 one of the liquid cements, by means of a 

 camel's-hair pencil ; and when the first coat 

 is dry, another must be laid on, so that the 

 edges of the cover and the adjacent parts of 

 the glass ring may be firmly cemented toge- 

 ther, and the cell completely closed, to pre- 

 vent the evaporation or the contained liquid. 

 The important points in this process are, 



