PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS. 179 



yet not so hard as to ' chip,' it is in the best condition to be used for cementing. 

 If too soft, it will require a little more hardening on the slide, to which it should 

 be transferred in the liquid state, being brought to it by the heat of a water-bath; 

 if too hard, it may be dissolved in chloroform or benzole, for use as a mounting 

 ' medium ' ( 205). 



g. Shell-lac Cement is made by keeping small pieces of picked Shell-lac in a 

 bottle of rectified spirit, and shaking it from time to time. It cannot be recom- 

 mended as a substitute for any of the preceding; as, when dry and hard, it has 

 little hold on glass. But it answers very well for making cells for dry-mounting 

 ( 167). What is known as Liquid-glue is an inferior kind of the same cement, 

 made by dissolving inferior shell-lac or some commoner resin, in naphtha. It 

 cannot be trusted for a permanent hold; and those who employ it are likely to find 

 themselves disappointed in regard to the durability of their preparations. 1 



h. Marine Glue, which is composed of Shell-lac, caoutchouc, and naphtha, is 

 distinguished by its extraordinary tenacity, and by its power of resisting solvents 

 of almost every kind. Different qualities of this substance are made for the 

 several purposes to which it is applied; and the one most suitable to the wants of 

 the Microscopist is known in commerce as G K 4. The special value of this 

 cement, which can only be applied hot, is in attaching to glass slides the glass or 

 metal rings which thus form * cells ' for the reception of objects to be mounted in 

 fluid; no other cement being comparable to it either for tenacity or for durability. 

 The manner of so using it will be presently described ( 171). 



i. Various colored Varnishes are used to give a finish to mounted preparations, 

 or to mark on the covering-glasses of large preparations the parts containing 

 special kinds of noteworthy structure. A very good black varnish of this kind is 

 made by working up very finely powdered lamp-black with gold-size. For red, 

 sealing-wax varnish made by dissolving red sealing-wax (the best is alone worth 

 using) in rectified spirit, is commonly used; but it is very liable to chip and leave 

 the glass, when hardened by time. The red varnish specially prepared for Micro- 

 scopic purposes by Messrs. Thompson & Capper (of Liverpool) seems likely to stand 

 better, but the Author's experience of it has been short. For white, ' zinc cement ' 

 answers well: which may be made by dissolving 1 oz. of gum dammar in 1 oz. of 

 oil of turpentine by the aid of heat; rubbing up 1 drachm of oxide of zinc with 

 an equal quantity of oil of turpentine (adding the latter by drop) into a creamy 

 mixture perfectly free from lumps or grii ; and then mixing the two fluids, which 

 must be well stirred together, and strained through a piece of fine muslin pre- 

 viously wetted with turpentine. Blue or green pigments may be worked-up with 

 this, if cements of those colors be desired. 



k. For attaching labels and covering papers to slides either of glass or wood, 

 and for fixing-down small-objects to be mounted ' dry ' (such ac Foraminif era, 

 parts of Insects, etc.), the Author has found nothing preferable to a rather thick 

 mucilage of Gum Arabic, to which enough Glycerine has been added to prevent 

 it from drying hard, with a few drops of some Essential oil to prevent the develop- 

 ment of mould. The following formula has also been recommended: Dissolve 2 

 oz t of Gum Arabic in 2 oz. of water, and then add l-4th oz. of soaked gelatine 

 (for the solution of which the action of heat will be required), 30 drops of gly- 

 cerine, and a lump of camphor. The further advantage is gained by the addition 

 of a slightly increased proportion of Glycerine to either of the foregoing, that the 

 gum can be very readily softened by water; so that covers may be easily removed 

 (to be cleansed if necessary) and the arrangement of objects (where many are 

 mounted together, 175) altered. 



169. Cells for Dry -mounting. Where the object to be mounted ( dry' 

 (i.e. not immersed either in fluid or in any ( medium') is so thin as to 

 require that the cover should be but little raised above the slide a ' cement 

 cell ' ( 170) answers this purpose very well; and if the application of a 

 gentle warmth be not injurious, the pressing- down of the coyer on the 

 softened cement will help both to fix it, and to prevent the varnish applied 

 round its border from running in. Where a somewhat deeper cell is 



1 From the appearance and smell of the Hollis's Glue recommended by Dr. 

 Heneage Gibbs, the Author cannot but believe that its nature is essentially the 

 same as that of ordinary ' liquid glue,' and that it is therefore liable to the same 

 objection. 



