Note 10 — PART I.

The appearance of a slide is vastly improved if the preparation be placed exactly in its centre. This may readily be done in the following manner:—Take some very finely-powdered Prussian blue, and rub it up in a mortar with a little of the weak gum solution (§ 11), so as to form a thin blue pigment. A quantity of this should be made, so as always to be at hand. A slide having been cleaned, the best surface is to be selected, and on the reverse side, by means of the self-centring turn-table, a small circle is to be drawn with a camel’s-hair pencil, charged with the pigment. In the centre of this ring, but on the opposite side of the slide, the section is to be placed, when it of course will occupy a position exactly central. When the slide comes to be finished, the blue ring may easily be removed with a wet rag.