902 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Towards the completion of the preparation, the slide may be inverted, 

 if necessary, and the small flame allowed to play directly on the edge 

 of the cover ; thus, careful treatment will dispose of all buhbles. 

 "\\ lien cold, the excess is easily removed with a moistened roll of 

 tissue paper ; and finally, after the cleansing, the slide should be 

 warmed just sufficiently to expel auy moisture that may have found 

 its way under the cover. If, after the ring is applied, and the pre- 

 paration otherwise completed, any metallic stain should show on the 

 cover or slide, it can he removed with a roll of tissue paper moistened 

 with hydrochloric acid. 



The arsenious acid also makes an excellent compound with the 

 antimony bromide ; and the highest-refractive-power white medium 

 that I have yet seen is made as follows : — Melt antimony bromide 

 and add to it while hot half its bulk of glycerin ; in this put arsenious 

 acid, little by little, shaking and heating at the same time, until by 

 its solution the bulk is increased three-fourths of one part, so that 

 the final mixture will be : antimony bromide 2 parts, glycerin 1 part, 

 arsenious acid 3/4 part, all in bulk. This compound is solid, or very 

 nearly so, when cold, and will require slight warming to take out a 

 drop on the dipping -rod. It does not soften much, if at all, on 

 exposure, and its refractive index is well on towards 2. The mounts 

 made with this material are very satisfactory. 



Finally, I think that the yellow medium, the compound of 

 ' realgar ' and bromide of arsenic, can be made permanent and easy 

 to use by the addition of a small excess of sulphur. The realgar is 

 broken up and dissolved by the aid of heat, in the bromide of arsenic. 

 The solution is evaporated until, when cold, it becomes so viscid as 

 to flow with difficulty ; enough sulphur is now added to increase its 

 bulk about one-sixth (I have not been able to determine the exact 

 proportions yet), and thoroughly dissolved ; it becomes now somewhat 

 more limpid, and is used as one would use balsam. It requires a very 

 light heat to boil, so the slide must be heated cautiously ; but there 

 is no difficulty in boiling, and this should be continued for a little 

 while, when the cover will settle down entirely free from bubbles, 

 and, if the user is careful not to slide it, may be gently pressed down. 

 When cold, the deep colour will disappear and the cover will be very 

 firmly fixed. To use this medium, the best polished slides must be 

 obtained, as all the pits and scratches of ordinary slides show up very 

 disagreeably. The cover also must be well cleaned. I have pre- 

 parations which w r ere made with this material more than three months 

 ago, that show no symptoms of change. 



Too much sulphur, however, will, in time, crystallize. I cannot 

 now state what proportions can be safely used, but the amount named 

 above, thus far appears within limits." 



At the meeting of the Microscopical Section of the Eoyal Society 

 of New South Wales on June 2nd,* specimens of Amphipleura 

 pellucida were exhibited mounted in piperine, pici'ic acid, chlorides of 

 tin and thallium and sulphur in combination with disulphide of 



* Ci: Nature, xxxiv. (1886) p. 355. 



