THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. VI. 



Washington, D. C, September, 1885. 



No. 9. 



Moiiiitini?: Media of Higli Refrac- 

 tive Index.* 



At the meeting- of the American 

 vSocietv c)t" Mici08Copists at Cleve- 

 hmd. Prof. H. L. Smith described 

 his process of mounting in media of 

 high retractive power, and gave the 

 formulas for preparing the same, and 

 we are enabled to present the follow- 

 ing abstract, which embraces the 

 principal points of interest. The 

 white medium, which has'a refractive 

 index of about 1.7, is very easily pre- 

 pared, and is pronounced by Prof. 

 Smith, and those who have used it, 

 as unchangeable, provided moisture 

 is kept out. The following is the 

 formula as given for this : — 



A stit^' glvcerin-jelly is first made, 

 about the consistency of honey, by 

 dissolving clear gelatin (Cox's) in 

 pure glvcerin, by aid of heat, and, 

 in two fluid drams of this, forty 

 grammes of pure stannous chloride 

 are dissolved. The solution is easily- 

 eflected bv a little heat. When this 

 solution is made it will probably be 

 somewhat milkv, but by boiling it in 

 a test tube it will become beautifully 

 clear, and about the color of balsam. 

 This boiling must be done in a test 

 tube not over one-fourth full, as the 

 bubbles are, towards the last, very 

 large, and thrown ^•iolentl^• up and 

 liable to eject the fluid from the tube ; 

 but with care the whole may, in a 

 short time, be made not only clear, 

 but, when cold, about as stiff' as thick 

 balsam ; and, if in a small vial, it is 

 not readily poured out. This medium 

 should be used in making mounts pre- 



* Revised by the author. 



cisely as balsam is when the mounts 

 are to be flnished by heating. The 

 bubbles escape very rapidly and 

 easily, but towards the end of the 

 boiling, as the medium becomes vis- 

 cid, they are inclined to persist, but 

 by carefidly heating, using a small 

 flame, they will disappear, and, in- 

 deed, as they are mostly steam, they 

 will frequently disappear wdiolly in 

 cooling, when a balsam mount under 

 the same circumstances would be full 

 of bubbles. 



If the boiling has been sufficienth' 



prolonged, on cooling the cover will 



be found to be pretty firmly attached, 



and will allow the excess of material 



to be cleaned off' without danger to 



the mount — indeed, this excess should 



be hard, requiring a knife or a sharp 



edge to i-emove it. It is advisable to 



; put on only so much as is necessary 



I to fill in under the cover, and have no 



{ cleaning to do afterwards, or put on 



a minute drop, and if that should not 



be enough teed in a little more from 



the end of the small glass rod used 



for dipping. The best thing to clean 



ort' the excess is hydrochline acid — a 



bit of tissue paper rolled up and 



j moistened with this, not too wet, 



serves the purpose admirably, but 



water may also be used, and is nearly 



1 as good. 



As the medium is deliquescent it is 

 necessary to use a protecting ring. 

 For this purpose, after the slide is 

 I well cleahed around the cover-glass, 

 and warmed to dry it, apply a good 

 j coat of zinc-white cement, or shellac, 

 ! colored to suit the fancy. If the seal- 

 ing is perfect there will be no change 

 ' by time. It is recommended, how- 



