1098 SUMMARY OF CURRENT RESEARCHES RELATING TO 



wholly in cooling, when a balsam moimt under the same circumstances 

 would be full of bubbles. 



If the boiling has been sufficiently prolonged, the cover will be 

 found, on cooling, to be pretty firmly attached, and will allow the 

 excess of material to be cleaned ofi' 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 necessary 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 off the excess is hydrochloric acid, a bit of tissue 

 paper rolled up and moistened with this, not too wet, serves the 

 purpose admirably, but water may also be used, and is nearly as 

 good. 



As the medium is deliquescent it is ne.essary 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 coloured to suit the fancy. If the sealing is 

 perfect there will be no change by time. It is recommended, how- 

 ever, to use a wax ring. These rings punched out of sheet wax, of such 

 size as to cover the edge of the thin glass, are put on the mount when 

 it is finished, and, by cautious application of a small flame, just 

 melted but not so as to run. If any bubbles form under the ring 

 they may be removed by touching with a hot needle or pin-point before 

 the wax cools. A mount made in this way will stand indefinitely and 

 can at any time receive a supplemental coloured ring of shellac or 

 other varnish for a finish. 



AmpM'pleura pellucida is very beautifully shown in this medium, 

 and the various Pleurosigmas, indeed all diatoms except the very coarse 

 ones, which appear almost black in the medium. A very little ex- 

 perimenting will enable one to use the medium successfully. 



The use of the gelatin is only to give such a hold upon the cover 

 as will permit the necessary pressure in cleaning. Many mounts 

 were made in the earlier experiments with this medium, without the 

 gelatin, but in all these cases the cover was less firmly attached to 

 the slide. If the protecting ring keeps out moisture from immersion 

 media, or the atmosphere, the mounts will remain unchanged. As 

 the medium dissolves gelatin, albumen, &c., arranged diatoms must 

 be fastened to the cover by heating the latter, supported on a bit of 

 thin sheet iron or platinum, nearly to a melting or softening point, 

 A larger proportion of the stannous chloride can be dissolved than 

 that mentioned above, even as much as 60 gr., but then on heating to 

 harden the mass, crystals will appear ; the crystals never give any 

 trouble when 40 gr. are used. 



In a subsequent note f Prof. Smith says, the refractive index may 

 be raised considerably by making a saturated solution % in the glycerin 

 jelly — about 60 gr. to the fluid dram — and mixing this with the 



* See the next note. f Amer. Mon. Micr. Journ., vi. (1885) p. 182. 



X By a saturated solution the author meaas one whicl), when thoroujhly cooled, 

 will show &igus of crystallization. 



