Fix the plate in hypo—­the fixing takes place very quickly—­then examine the picture for the faults above described; if they are found, wash the plate under the tap gently, and bring into operation a camel’s hair brush and a weak solution of cyanide of potassium.  Apply the brush to the over-printed parts, taking care not to work on the places that are not too dense.  Do not be afraid to use plenty of washing while this is being done; let it be, as it were, a touch of the brush and then a dash of water, and you will soon reduce the over-printed parts.  It only requires a little care in applying the brush.

After this wash well, and should it be deemed necessary to tone to a black tone, use a weak solution of bichloride of platinum and chloride of gold, or a very weak solution of iridium, in equal quantities, allowing the picture to lie in the solution till the color has changed right through to the back of the glass.  Should a warm pinkish tone be desired, I tone with weak solutions of ferri cyanide of potassium, nitrate of uranium, and chloride of gold in about equal quantities.

After toning, wash well and dry; they dry quickly.  Varnish with Soehnee crystal varnish, then mount with covering glasses, and mark.  Bind round the edges with paper and very stiff gum, and the picture is complete.

The making of a really good transparency is by no means an easy or pleasant task with a wet collodion plate, but with these dry plates an amateur can, with a little practice, produce comfortably slides quite equal to those procurable from professional makers.

* * * * *

THE HONIGMANN FIRELESS ENGINE.

The invention of a self propelling engine, capable of working without fuel economically and for a considerable time, has often been attempted, and was, perhaps, never before so nearly accomplished as about the time of the introduction into practical use of Faure’s electric storage batteries; but at the present moment it appears that electric power has to give way once more to steam power.  Mr. Honigmann’s invention of the fireless working of steam engines by means of a solution of hydrate of soda—­NaO HO—­in water is not quite two years old, and has in that time progressed so steadily towards practical success that it is reasonable to expect its application before long in many cases of locomotion where the chimney is felt to be a nuisance.  The invention is based upon the discovery that solutions of caustic soda or potash and other solutions in water, which have high boiling points, liberate heat while absorbing steam, which heat can be utilized for the production of fresh steam.  This is eminently the case with solutions of caustic soda, which completely absorb steam until the boiling point is nearly reached, which corresponds to the degree of dilution.  If, therefore, a steam boiler is surrounded by a vessel containing