Glycerin Jelly as a Substitute for Hoyer's Solution Mountant
Glycerin Jelly as a Substitute for Hoyer's Solution Mountant
Problems arise when microscope slides are made, as is commonly the case in bryology, with Hoyer's Solution. The slides remain sticky too long and arrive through the mail smeared. Also, some researchers may not have access to Hoyer's Solution as a mounting medium because a main ingredient, chloral hydrate, is a controlled substance.
You can make an acceptable mounting medium with glycerin jelly. Simply make the jelly according to standard formulae or
1. dissolve a packet of granulated gelatin (available in grocery stores; about 7 grams per packet) in enough cold water to hydrate it, stirring well, then heat to fully dissolve.
2. add 50 to 100 ml of drugstore glycerin, stirring with continued mild heating until mixed well.
3. pour the hot solution into a flat dish.
4. let harden overnight - and let the water portion evaporate for a day or so preferably in a hot place like a† herbarium drier.
5. the nearly pure gelatin and glycerin mixture is now scored into long "worms" and removed from the plate.†
[Note on March 15, 2010: Roll the flat, thin sheet of glycerin jelly (which peels off a PVC pan easily if you let it sit for a couple hours) into a long jelly-roll. Then, snip across into tight coins, which can be peeled into long strings. Use finger-nail to snip off a bit of jelly-string for use.]
The glycerin jelly will be hard to remove from the plate unless the water portion has evaporated. It is best to evaporate the water portion with heat since glycerin absorbs water, to some extent, from the air.
Method A: Put your plant material on a slide in water, soak, add pure glycerin and heat with a cigarette lighter so the water evaporates somewhat and the plant material plumps up with glycerin after an initial collapse. Make sections, etc. Take a strip of glycerin jelly and pinch off a portion, put on the slide with the glycerin-heated material and heat some more being careful to apply the heat rather generally rather than in only one spot (which can crack the slide). Arrange material and gently add a cover slip. It hardens in a minute and may be mailed when cool - which is almost immediately after labeling. Don't worry about the clearing aspect of Hoyer's solution, material usually doesn't have to be cleared to be studied or illustrated, or if you must clear it, dip the most plant in lactic acid for a minute or so (or heat in the pure acid) before preparing the glycerin jelly mount.
Method B: I have a small hot plate near my microscope. I set a microscope slide with the wetted plant (or sectioned material) in a little water (or a mixture of water and a little glycerin) and a cube of glycerin jelly on the hot plate. After a moment or two, the glycerin jelly melts and some of the extra water evaporates. I remove the slide, arrange the material and put a cover slip on it. The hot plate is one of those coffee warmers you can pick up in a flea market for a buck or two. This eliminated heating a cube of glycerin jelly on a slide, which can break the slide if not it is heated evenly with the cigarette lighter. The hot plate warms up whenever the microscope light is switched on.
Note: Although you can put a dropper bottle of glycerin jelly on the hot plate, the heat eventually turns the jelly brown, and the gelatin breaks down so that it will not harden.
Another note: Glycerin dissolves (eventually) calcium carbonate.
Also, if you make the glycerin jelly with a high concentration of gelatin, then if you work on your specimen in a water/glycerin mixture (which slows sections from flying around when you make them] then any added glycerin jelly will not be too dilute (when mixed with the pure glycerin on the slide] to harden.
See also: Zander, R. H. 1997. On mounting delicate bryophytes in glycerol. Bryologist 100: 380Ė382.
[March 15, 2010: Try this formula to make stiff glycerin jelly that will allow you to work in glycerin, then add the jelly and it will still harden even though diluted:
Take 2 packets (2 time 7 g) of gelatin,
Mix in 50 ml cold water to hydrate,
Heat but don't boil while still stirring, until the liquid is clear or at least there are no undissolved gelatin,
Swirl it to dissolve all gelatin,
Add glycerin to 200 ml,
Heat for about an hour until dissolves and the liquid is clear,
Pour on a clean pvc pan to make a thin layer,
Leave uncovered overnight or a couple days to allow water to evaporate,
Peel off the thin, flat sheet of glycerin jelly,
Roll into a kind of jelly roll,
Slice the roll crosswise into neat, tight curlicues or helixes about 1/4 inch wide,
Keep in a plastic box,
Pinch off a small piece when wanted.
If there are bubbles, reheat in a beaker (water bath is good) and let stand as liquid. Do not keep hot for a very long time, as heat denatures the gelatin.]
[Another note, this time to Bryonet Nov. 9, 2009:
Technique with Mniaceae and other large-celled bryophytes: strip leaves in water or Pohlstoffe solution or 2% KOH, then add 2 tiny drops of pure glycerin to the water or solution mount. Do cross sections and arrange leaves nicely in the unmixed water/glycerine mount, add a fingernail sized clod of glycerin jelley, heat with one of those butane lighters with the nice torch flame taking care to heat the slide fairly evenly so it does not break, heating until the glycerin jelly just melts or before it is completely melted, rearrange the leaves and whatever else is on the slide, plop on a cover slip, and after it cools it is solid and ready to mail or bang around the lab without drying. Don't use 2% KOH with liverworts as the leaf cell walls are attacked.
Mounting in water and glycerin first, then heating plumps up the leaf cells with glycerin, then add the glycerin jelly. The slides are permanent if you keep them in a sealed cabinet with a small dish of glycerin to saturate the air with glycerin. Donít stack the slides because pressure causes any added pure glycerin to leak out, since it does not integrate entirely with the jelly even when heated.]
Note on January 8, 2011: The glycerin jelly mounts are like little sponges. Do not stack slides as the pressure will squeeze glycerin from the mounts and make a mess. This is true even if you do not add pure glycerin in the mounting stage.