Edward Leonard, 1875 - 1931

Before proceeding with instructions as to the actual mounting, it would be well that I should describe to you the apparatus and materials I use. The order that I shall mention them in is exactly the order in which they would be made use of in mounting:

1. A “searching-over” slip, 3 by 1, ruled with a diamond very lightly in vertical lines 1/25 inch to 1/50 inch apart. It is best when preparing these to make half a dozen, not only to allow for breakages, but also for the drying-off at one time of three or four slips containing the “dips” to be searched over.

2. A piece of glass tubing 3/32 inch internal diameter and about 6 inches long. The tube out of the old style of baby's feeding-bottle is just the right size. This tube is narrow enough to allow a cotton-and-wire pipe-cleaner to thoroughly cleanse it of any stray discoid forms that might be hanging around from previous dippings. I always make it a rule, after every dip, to clean the inside of the tube with the pipe-cleaner and wipe the outside with a clean handkerchief. Thus no diatoms from one locality can be confounded with those from another. Of course, this also prevents the wonderful discovery of a marine form in a fresh-water lake 200 miles inland! A pipette which narrows at the mouth is apt to cause trouble on this account, as it cannot be cleaned freely like a straight tube.

3. An ordinary slip with a small circle thereon about 1/8 inch in diameter, to store diatoms in as picked off the “searching-over” slip. For convenience in working, both slips should be of exactly the same thickness.

4. A turntable.

5. Some carmine or other color water-color in blocks, not moist color in pans. I use Windsor and Newton's best carmine, at 7d. a half-cake. This will last a lifetime. Moist color seems to have some spirit in its composition which does not agree with my fixatif. To bring into use, put a little water on a bit of glass or china, and grind end of cake round and round until a sufficiency for ringing is made up.

6. A sable brush as fine as possible (size “00,” if one can get it) for making guide-rings.

7. A “fixatif” of two densities—one for fine diatoms, and one for heavy forms. The fixatif I use is made up as follows: 100 parts collodion (B.P. formula), 500 parts absolute alcohol, 500 parts methyl-ether, 25 parts pure oil of cloves. This density can be used for most forms; but for very fine diatoms I use a mixture containing 750 parts each alcohol and ether, other proportions (100 collodion and 25 oil of cloves) remaining the same. Mix the collodion, alcohol, and ether, and then add oil of cloves. Keep bottles well corked.

8. Two or three hairs mounted in penholders—fine, medium and heavy. Any fine, flexible hair is suitable. I use cat's whisker-tips; they are excellent. Sharpen penholder to a point, pierce as fine a hole as possible, then with forceps drop in hair; have a drop of Hollis's glue on point of a needle, and apply to base of hair; glue will run in, and when dry the hair is fast. I have only 1/4 inch to 3/8 inch of hair in use. I do not believe in a long hair; it affords less control.

9. Some sort of support for cover-glass where specimen has thickness or processes. Broken cover-glass will do; but I use tiny discs of aluminium about 3/1000 inch in thickness. (See description in the Quekett Microscopical Journal for April, 1892.) I do not know that these can be obtained ready-made.

10. A spirit-lamp and water-bath.

11. Some watch-glasses to use as covers while fixatif is drying.

12. Xylol.

13. Styrax and xylol.

14. Hollis's glue or brown cement for ringing.

The above sounds a somewhat formidable list; but most mounters will find they have the bulk of the materials by them already, and none of the articles listed are expensive.

As to the instrument under which I mount, it is a Swift-Stevenson's special mounting binocular. This greatly simplifies one's work, but is by no means a necessity. Firth, of Belfast, whose beautiful work (groups sometimes of 200 forms) is well known to many readers, uses an ordinary inclined model with a small stage. It is, however, a very good thing to make some wood blocks, sloping upward, so as to bring the wrist to about the level of the stage.

If one has a flat stage, then I strongly recommend a tray such as I will describe. It is about 3 1/2 inches long by 2 1/2 inches wide, with narrow strips of glass cemented on three sides. You thus have a tray on which two 3 by 1 slips will be side by side, and move continuously in the same plane. At the bottom of the tray can be placed the “searching-over” slip, and above it the storing-slip Thus one has always one's store-cell ready to hand, and the risk of losing a specimen in transferring from one slide to another is practically eliminated.

Now that I have described all the materials necessary, I will proceed to the actual mounting. Take a bottle of clean diatoms. Gently shake the bottle, and insert end of tube. By placing one's finger over the other end, a certain amount of water and diatoms can be withdrawn and transferred to the “searching-over” slip. Start at one end of the latter, and draw tube along center, and, if slide be clean, one should have an evenly-distributed quantity of diatoms, sand, etc., the whole length of the slide—no thick patches, waves, etc. Then put slide on the “hot-plate” - but the latter, to commence with, must be quite cold - and gently warm up till slide is dry. If diatoms were really clean and free from acid, then there ought not to be any case of the diatoms adhering to the “searching-over” slip. Of course, with very fine forms like Pleurosigma, etc., there is nearly always considerable difficulty in this respect. Generally it is easiest to pick such out wet, balancing diatom on extreme end of hair, and finding, if possible, a broken spicule or something on which to deposit diatom while drying, and when dry transferring to store-ring. For picking out, I use a medium hair. If a big form is stubborn, I give it a gentle push with heavy hair, and usually that is sufficient to move it. If it will not, have a small bottle of distilled water handy, and keep on jabbing point of hair below surface until a small globule adheres to hair, then transfer globule to close by the diatom to be moved, and with point of hair draw water toward diatom. Once loosened, keep the latter moving until dry again, when generally you will find it ready to transfer to store-cell. If still refractory, leave if a common form; go at it again if scarce.

If there is dirt on the diatom, remove latter to a cleaned slip (not the store-cell, but one with no ring on), pick up a globule of distilled water on finest hair, envelop the diatom with same, and then shove the diatom about, beat it, prod it, prick it, tickle it, or do anything you like (except break it), and usually you can get the dirt away—of course, under water all the time, the water acting as a cushion between the diatom and one's often impotent fury! Beware of prodding hard a diatom that sticks when dry: he either “busts” or disappears into space like a stone from a catapult.

Now, having caught your hare, proceed to cook it, first preparing your utensils.

Except for very delicately marked specimens, I always mount on the slip, using thin cover-glasses. Modern objectives have plenty of working distance. Take a 3 by 1 slip, clean thoroughly, then put on turntable, and in center of slip make a neat and small guide-ring: 1/16 inch internal diameter is quite big enough for three or four ordinary specimens. To those who are not in the habit of making these small guide-rings I would recommend a couple of hours' practice making such rings. A neat ring looks nice under the instrument; but an untidy one will leave an unpleasant recollection, no matter how beautiful the specimen may be. These remarks not only apply to diatoms, but to all objects which need a guide ring. By the way, these guide-rings serve a double purpose. No doubt everyone knows the great difficulty of trying to locate a very minute object under 1/4 inch or higher power. The guide-ring fills the field of a sixth, and when once you have found the ring, it is easy enough to find the diatom if the latter is mounted in center of guide-ring, as it should be. Another point gained is that one can focus the paint, and know that one's object is also in focus, or very nearly so. The latter, however, only applies to objects mounted on slip, and not to those mounted on cover-glass.

I omitted to say that I keep the collodion fixatif in tubes about 7/8 inch by 3 inches, and they must have perfectly-fitting corks, or it will be found one day that the ether and alcohol have evaporated, leaving a thick jelly which is of no use at all. Into each cork I stick about 2 inches of fine quill. Near the cork, a notch must be cut, and the lower end of quill should be cut square, not slanting. The quill, of course, goes right down into the fixatif, and when cork is drawn out, about 3/8 inch of quill is full of fixatif.

Now to proceed. After making a guide-ring, hold slip over lamp until it is quite hot, and all moisture driven off: moisture does not agree with collodion, and if present causes clouding, which, however, can be driven off by reheating. Still, prevention is better than cure. While the slip is still hot - hot as your fingers will stand - draw cork out of fixatif-bottle, tilt slip to an angle of 45 degrees, and apply tip of quill to surface about 1/8 inch to 1/4 inch above the guide-ring. The fixatif will immediately leave quill and spread itself nicely around. It does not matter if it goes beyond area coverable by cover-glass, as it can be cleaned off afterward by breathing on it and rubbing with a soft rag. This latter to be done, of course, only when slide is hardened off.

At this stage of the proceedings I put on my coverglass supports, placing them triangularly about 1/8 inch from edge of guide-ring. They can be easily pushed into position with a fine needle. See they are well buried in the fixatif, or later on, when heating, they may slip and spoil appearance of slide. Next put slip under the microscope, and if slightest bit of dust inside guide-ring, push or draw it out with stout hair, and everything is ready to put your object into place. Pick up the diatom (right side up) by the hair that has been used for removing dust from guide-ring (it will be a bit sticky, and diatom will adhere), and then place diatom in center of ring, or, if you are mounting more than a single specimen, as near to final position as possible. Do not be alarmed if it buries itself in the fixatif, or looks as if it had taken down air with it, but see that it lies nice and flat. Fixatif, owing to the oil of cloves, remains tacky from thirty to fifty minutes, so that one can mount forty to fifty specimens (or more) if one wishes. When you have in position all the diatoms you are mounting on that particular slip, put the latter on hot-plate, pop a watch-glass over it, and leave for twenty to thirty minutes. This should drive off alcohol, ether, and oil of cloves, leaving diatoms firmly fixed in a very thin film of collodion, as also the coverglass supports. For fine diatoms, use lighter density of fixatif. After this drying-off, push diatom gently with stout hair, and if diatom does not move, you may consider it ready for next step. Put slip on microscope stage, and with a pipette (fine-pointed) drop the smallest quantity possible of pure xylol on the diatoms (mind you do not smash specimens in doing this). If whole diatom clears at once, well and good, and you can proceed to drop some styrax on it. I use only 3/8 inch cover-glasses (No. 1's), and find one drop of styrax plenty to fill up the area of 3/8 inch. Big circles probably need more. Then put slide, as it is, with styrax, back on the hotplate, cover with watch-glass, and leave for another twenty or thirty minutes; then take off, and put on cover-glass, replace on stove, and the cover-glass will quickly make contact and settle into place. Finally, completed slide ought to have twenty-four hours baking on a hot-plate at a temperature of 130 degrees to 140 degrees, when by that time it should be impervious to oil of cedarwood or anything else. But the slide will take no harm from a ringing of Hollis's glue or Brown's cement. By the way, solvent for Hollis's glue is wood-naphtha.

To revert. If xylol does not quite clear the specimens, but leaves a little air still showing as a bubble, sit and watch it until all the air disappears, and then put on styrax, and proceed as before mentioned. If bubble is very stubborn and not inclined to disappear, have some xylol in a wide-mouthed stoppered bottle, and put slide in and leave for a time (hours or days), when it is almost certain to clear, and can be finished off. By the way, it is as well to put some sort of a mark on the top surface of slide, as when slip is withdrawn from xylol bottle it is difficult to tell which side of it the diatom is on. I scratch a number on corner of slip with a diamond, and that number can also be used as an index to jot down locality from which the diatom is taken.

Possibly, after dropping on styrax, air-bubble will reappear. I do not understand why, but it does so, though such a bubble nearly always disappears during the twenty-four hours' baking. Should you find it necessary to remove any dirt, or specimen, after hardening the fixatif (but before styrax is put on), the fixatif can easily be softened by dropping on a little pure alcohol (not ether, as the action of the latter is violent).

For baking slides after completion, I use an ordinary copper breakfast hot-plate, substituting a small Bunsen burner for the spirit-lamp, keeping the temperature at about 130 degrees to 140 degrees for twenty-four hours. At the end of that period you will find the styrax that has exuded from underneath the cover-glass very stiff and tacky, even while hot, and quite hard when cold. Superfluous styrax should be removed with a rag dipped in xylol or methylated spirit.