A matter of first importance, after drying the herbarium specimens, is to poison them, to prevent the attacks of insects. This is done by brushing them over on both sides, using a camel's-hair pencil, with a solution of 2 grains of

corrosive sublimate to an ounce of methylated spirit. In tropical climates the solution is generally used of twice this strength. There are several methods of mounting them. Leaves with a waxy surface and coriaceous texture are best stitched through the middle after they have been fastened on with an adhesive mixture. Twigs of leguminous trees will often throw off their leaflets in drying. This may, in some measure, be prevented by dipping them in boiling water before drying, or if the leaves are not very rigid, by using strong pressure at first, without the use of hot water. If the specimens have to be frequently handled, the most satisfactory preparation is Lepage's fish glue, but a mixture of glue and paste, with carbolic acid added, is used in some large herbaria. The disadvantage of using glue, gum, or paste is that it is necessary to have some of the leaves turned over so as to show the under surface of the leaf, and some of the flowers and seeds placed loose in envelopes on the same sheet for purposes of comparison or microscopic examination. Another plan is to use narrow slips of gummed stiff but thin paper, such as very thin parchment paper. These strips are either gummed over the stems, etc., and pinched in round the stem with forceps, or passed through slits made in the sheet and fastened at the back. If the specimens are mounted on cards and protected in glass frames, stitching in the principal parts with gray thread produces a very satisfactory appearance.

Hectograph Pads and Inks

The hectograph is a gelatin pad used for duplicating letters, etc., by transfer. The pad should have a tough elastic consistency, similar to that of a printer's roller. The letter or sketch to be duplicated is written or traced on a sheet of heavy paper with an aniline ink (which has great tinctorial qualities). When dry this is laid, inked side down, on the pad and subjected to moderate and uniform pressure for a few minutes. It may then be removed, when a copy of the original will be found on the pad which has absorbed a large quantity of the ink. The blank sheets are laid one by one on the pad, subjected to moderate pressure over the whole surface with a wooden or rubber roller, or with the hand, and lifted off by taking hold of the corners and stripping them gently with an even movement. If this is done too quickly the composition may be torn. Each succeeding copy thus made will be a little fainter than its predecessor. From 40 to 60 legible copies may be made. When the operation is finished the surface of the pad should be gone over gently with a wet sponge and the remaining ink soaked out. The superfluous moisture is then carefully wiped off, when the pad will be ready for another operation.

The pad or hectograph is essentially a mixture of glue (gelatin) and glycerine. This mixture has the property of remaining soft yet firm for a long time and of absorbing and holding certain coloring matters in such a way as to give them up slowly or in layers, so to speak, on pressure.

Such a pad may be made by melting together 1 part of glue, 2 parts of water and 4 parts of glycerine (all by weight, of course), evaporating some of the water and tempering the mixture with more glue or glycerine if the season or climate require. The mass when of proper consistency, which can be ascertained by cooling a small portion, is poured into a shallow- pan and allowed to set. Clean glue must be used or the mixture strained; and air bubbles should be removed by skimming the surface with a piece of card-board or similar appliance.

Variations of this formula have been proposed, some of which are appended:

I

Glycerine......... 12 ounces

Gelatin........... 2 ounces

Water............ 7.5 ounces

Sugar............ 2 ounces

II

Water............ 10 ounces

Dextrin.......... 1.5 ounces

Sugar............ 2 ounces

Gelatin........... 15 ounces

Glycerine......... 15 ounces

Zinc oxide........ 1.5 ounces

III

Gelatin........... 10 ounces

Water............ 40 ounces

Glycerine......... 120 ounces

Barium sulphate . . 8 ounces The Tokacs patent composition, besides the usual ingredients, such as gelatin, glycerine, sugar, and gum, contains soap, and can therefore be washed off much easier for new use. The smoothness of the surface is also increased, without showing more sticking capacity with the first impressions.