112 THE MICROSCOPE. 



crystals of salts and other objects. The object required to 

 be mounted is placed on the slider in its dry state, or de- 

 posited wet and allowed to dry; or if in solution, a drop 

 of the liquid is to be placed on the slip of glass, and 

 allowed to crystallise by spontaneous evaporation ; in the 

 latter case, take a drop of a warm saturated solution of the 

 salt required, and when a good group of well-defined crystals 

 has been obtained, break through the marginal ring of 

 crystalline deposit with a small point of wood, and carefully 

 conduct off the uncrystallised portion or mother-liquor to 

 the extremity of the slide, at the same time placing it in a 

 vertical position to drain until it is dry. A small quantity 

 of castor-oil is to be next carefully dropped on the subject, 

 and guided over the field with the point of a needle; in 

 this way it readily displaces the air and occupies the most 

 minute cavities. After a short time the upper glass is to 

 be placed on the surface, taking care to lower it gradually 

 so as to exclude the air; if the field is too full of oil, the 

 excess may be removed by a small piece of bibulous paper; 

 and if, on the contrary, sufficient oil has not been used, an 

 additional portion can be readily introduced by the capillary 

 action between the glasses. The shell-lac varnish is then 

 to be used as the cementing medium in the same way as 

 has been described, and with the same precautions. This 

 varnish cannot be replaced by either of the others, as it is 

 actually necessary (and this should always be borne in 

 mind) that there should exist no affinity between the fluid 

 in the cell and the varnish used to seal it permanently. 

 Hundreds of excellent objects have been lost from this 

 cause, and much valuable time and labour thrown away. 



A moderately strong solution of Arsenious Acid is found 

 to answer well for the preservation of animal substances ; 

 it is prepared as follows : Boil some arsenious acid in 

 distilled water ; when saturated, dilute with four to six 

 parts of distilled water, and filter it for use. Keep in a 

 stopped bottle. 



Mr. Goadby' s fluids are cheap and most effectual for 

 preserving and mounting animal structures in. The fol- 

 lowing are his formulae : 



Take for No. 1 solution, bay salt, 4 oz. ; alum, 2 oz. ; 

 corrosive sublimate, 2 grains ; boiling water, 1 quart : mix. 



