zooLoar and botany, miceoscopt, etc. 357 



clean off the cover before ringing), I was surprised to find that not 

 only had the leakage stopped, but that the drop outside was indurated, 

 and when removed the whole seemed perfectly sealed, and showed no 

 tendency to the smearing when wiped hard, that had caused me at 

 first to suppose these mounts were sjioiled, and they remain up to the 

 present moment now apparently good. The boro-glyceride 50 per 

 cent, solution will not permit as much chloride of tin to be dissolved 

 as I mentioned in the directions for the gelatin preparation. A 25 

 or 30 per cent, solution will be better here, and this medium still 

 answers admirably for ordinary diatoms. 



The gelatin and tin compound is more hygroscopic than the 

 compound of boro-glyceride and antimony ; still, if properly made 

 and used will answer admirably and remain unchanged, I believe, 

 for any length of time." 



Meates' New Medium of High Refractive Index. — Mr. W. C. 

 Meates describes a still newer medium : — In a clean dry test-tube 

 put 10 grains of bromine, and 30 gi-ains of suljjhur. Boil gently 

 until the sulphur is dissolved ; then add 13 grains of jiowered arsenic 

 (metallic) ; again boil gently until the whole of the arsenic is 

 dissolved. The result is a medium of a light yellow colour with a 

 high refractive index (2*4), and easily melted at a low degree of 

 heat. It does not crystallize. When it is boiling, fumes of bromide 

 of arsenic are given off, which are deposited on and forced up the 

 sides of the test-tube ; therefore, when these fumes nearly reach the 

 top of the tube, the boiling should be discontinued for a few seconds 

 and the mixture agitated, in order that the bromide may be again 

 absorbed. Then boil again, and so on until the arsenic is dissolved, 

 when the mixture will be ready for use. 



There is no occasion for making more than the quantity indicated, 

 as a small drop, when warmed, no bigger than a small pin's head, 

 taken up on a finely drawn out piece of small tubing, is quite sufficient 

 for a slide. When the slide is warmed it spreads into a very thin layer. 



Morris's Mounting Medium.* — Dr. W. Morris suggests another 

 mounting medium, of high refractive index. The method of prepara- 

 tion is said to be exceedingly simple, and the whole process need 

 not take more than two minutes. To equal parts of sulphur and 

 disulphide of arsenic 1/20 part of biniodide of mercury is added; 

 the whole is fused on a piece of mica, then sublimed on to the cover- 

 glass, finally remelted on the cover-glass and mounted in Canada 

 balsam. The very thinnest cover-glass may be used. American 

 slides recently received have a cover-glass with the thickness of • 009 ; 

 Dr. Morris's cover-glasses are only O'OOl. 



Seaman's Mounting Media of High Refractive Index.f — Prof. 

 W. H. Seaman has tried oil of cassia (the refractive index of which 

 is nearly equal to that of carbon bisulphide) making a saturated 

 solution of phosphorus in the oil. This mixture is easier to use 

 because less inflammable than carbon bisulphide, but contains less 



* Australasian Med. Gaz., v. (1S86) p. 100. 



t Amcr. Moji. Micr. Journ. vii. (1886) pp. 21-4. 



