14 JOURNAL OF THE [January, 



When it is properly prepared, and care is used not to over- 

 heat, the medium will be of a deep amber color, and will make 

 mounts which are almost absolutely colorless. The refractive 

 power is considerably more than can be obtained with the stannous 

 chloride medium. As the boro-glyceride alone becomes hard 

 upon heating and evaporating the excess of gelatine, we can, if 

 for some objects a medium of lower refractive index is desired, 

 make the compound to have whatever refractive power may be 

 necessary up to fully 1.8, or, it may be, more. The specimen 

 which I send herewith for inspection by the Society, was made in 

 the stock bottle without any attempt at the purification or filter- 

 ing of the solution. The medium is used in the same manner as 

 balsam, and, if properly made, will have the consistency of thick 

 balsam ; a small dip is taken out on a glass rod and applied to a 

 warmed slide, and on this the cover is placed, the diatoms 

 having been previously dried and burned upon it. The whole 

 is now heated and boiled, as in making a balsam mount. The 

 boiling is prolonged somewhat more perhaps than in making a 

 balsam mount, but the medium works very kindly, and the cover 

 will settle down and the bubbles all disappear on cooling ; if 

 not, the heat can be again applied and the few remaining bubbles 

 coaxed out, and now, if the boiling has been sufficiently pro- 

 longed, the cover will be found as securely fixed when the slide 

 is quite cold, as it would have been if Canada balsam treated in 

 the same way had been used. As the material remains soft 

 with comparatively little heat, the slide must be entirely cooled 

 before proceeding to clean off the excess of the medium, if there 

 be any. As the medium is quite soluble in water (which, how- 

 ever, turns it white), the excess can be easily and quickly remov- 

 ed by using a little roll of moistened tissue paper ; and without 

 any fear of disturbing the mount, the slide and all around the 

 cover must be wiped quite dry, and, to insure this, perhaps a 

 slight reheating will be best. If, however, reheating is indulged 

 in, the slide must be allowed to cool before applying the finish- 

 ing ring. 



I have been using a cement made of gold size and litharge, 

 which dries rapidly, and appears to make an excellent, tough, 

 and hard finishing ring. I prefer, however, the wax ring, punch- 

 ed out from the ordinary sheet wax as prepared for artificial 



