356 SUMMABY OF CURRENT RESEARCHES RELATING TO 



as hairs and fur-fibres in particular rosin is preferable to balsam as a 

 medium for mounting. 



Smith's Newer Mounting Medium of High Refractive Index.* — 



Prof. Hamilton L. Smith has recently discovered a mounting medium 

 which he regards as superior to any hitherto described. It is even 

 superior to the preparations described last year."f These consisted of 

 stannous chloride in glycerin jelly, giving a refractive index of 1 • 7, 

 and of realgar in arsenic bromide, with a refractive index of 2*4. 

 The new medium, which has a refractive index considerably above 

 that of the stannous chloride medium, is prepared in the following 

 manner : — 



Dissolve 1^ oz. of antimony bromide in two fluid drachms of a 

 50 per cent, solution of boro-glyceride. This, when cold, makes a 

 very viscid medium, like old stiff balsam, of a dark, sherry wine 

 colour. Mounts made with it in the extremely thin film required are 

 as colourless as with old balsam, and when laid upon white paper, 

 the colour of the medium is scarcely perceptible, if it has not been 

 injured by overheating — certainly less than most mounts in styrax. 

 It is used precisely like Canada balsam. It works easily at a 

 moderate heat, and boils very rapidly. The heat must be continued 

 until the boiling is nearly over, but care must be observed not to 

 overheat, as the glycerin is likely to burn. When entirely cooled, 

 the cover will be firmly attached, as with balsam, and the slide may 

 be cleaned with moist tissue paper, without fear of disturbing the 

 cover. 



A finishing ring may now be applied, but Prof. Smith advises that 

 a bit of paraffin should be placed on the slide, melted, and caused to 

 flow around the mount, by tilting the preparation. A vigorous 

 rubbing with a cloth will remove all excess of paraffin, leaving a 

 sloping or bevelled ring round the mount. This operation has 

 preserved mounts for two months already, with no indication of 

 change. Any finishing cement may then be applied. 



The medium is only slightly deliquescent, but is 'decomposed by 

 water, and injured by contact with immersion fluids — hence some 

 protection is necessary. 



We now quote from Prof. Smith's letter as follows ; — 



" The boro-glyceride which I have used was prepared for me by 

 Mr. C. F. Booth, of Tarrant & Co., manufacturing chemists, JSTew 

 York. This substance is a hard, brittle, and glassy compound of 

 glycerin and boracid acid, and will no doubt serve an excellent pur- 

 pose as a mounting material from its antiseptic properties. I use a 

 50 per cent, of this in glycerin. 



I wish to say here that recently, in looking over some of my 

 earliest mounts in the chloride of tin and glycerin medium that I 

 had thrown aside because of leakage (as this material, before I used 

 gelatin, always remained more or less soft, and so made it difficult to 



* Amer. Mon. Micr. Journ., vii. (1886) pp. 3-4. 

 t See this Journ., v. (1885) p. 1097. 



