THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL, 



Vol. VI. Washington, D. C, September, 1885. 



No. 9. 



Mounting Media of Higli Reft'ac- 

 tive Index.* 



At the meeting of the American 

 vSociety of Microscopists at Cleve- 

 hmd. Prof. H. L. Smith described 

 his process of mounting in media of 

 high refractive power, and gave the 

 formuhis 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 1.71 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 stift' glycerin-jelly is first made, 

 about the consistency of honey, by 

 dissolving clear gelatin (Cox's) in 

 pure glycerin, by aid of heat, and, 

 m two fluid drams of this, forty 

 grammes of pure stannous chloride 

 are dissolved. The solution is easily 

 eflected by a little heat. When this 

 solution is made it will probablv be 

 somewhat milky, 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 violently 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 stifi'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 finished 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 carefully heating, using a small 

 flame, they will disappear, and, in- 

 deed, as they are mostly steam, they 

 will frequently disappear wholly in 

 cooling, when a balsam mount under 

 the same circumstances would be full 

 of bubbles. 



If the boiling has been sufficiently 

 prolonged, on cooling the cover will 

 be found to be prett)' firmly attached, 

 and will allow the excess of material 

 to be cleaned ort' without danger to 

 the mount — indeed, this excess should 

 be hard, requiring a knife or a sharp 

 edge to remove it. It is advisable to 

 put on only so much as is necessarv 

 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 feed in a little more from 

 the end of the small glass rod used 

 for dipping; The best thing to clean 

 ofl' the excess is hydrochline acid — a 

 bit of tissue paper rolled up and 

 moistened with this, not too wiet, 

 serves the purpose admirably, but 

 water may also be used, and is nearly 

 as good. 



As the medium is deliquescent it is 

 necessary to use a protecting ring. 

 For this purpose, after the slide is 

 well cleaned around the cover-glass, 

 and warmed to dry it, apply a good 

 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- 



