Nitrate of Silver 30 grains. Glacial Acetic Acid 30 minims. Water 1 fluid ounce. Float the papers (Papier Saxe or Papier Rive) upon the Bath for three minutes, and suspend them to dry in a room from which actinic rays are _perfectly_ excluded. The exposure to light,--which is conducted in the ordinary printing frame, the Negative and sensitive paper being laid in contact in the usual way,--will seldom be longer than three or four minutes, even upon a dull day. It may be regulated by the colour assumed by the projecting margin of the paper; but it is quite possible to tell by the appearance of the image when it has received a sufficient amount of exposure:--the whole of the picture should be seen, excepting the _lightest shades_, and it will be found that very few details can be brought out in the development which were altogether invisible before the Gallic Acid was applied. The developing solution is prepared as follows:-- Gallic Acid 2 grains. Water 1 fluid ounce. In very cold weather it may be necessary to employ a saturated solution of Gallic Acid, containing about four grains to the ounce; whereas in warm weather the image will develope too quickly, and Acetic Acid must be added (see the remarks at the end of the process, p. 266). To facilitate the solution of the Gallic Acid, stand the bottle in a warm place near the fire. A lump of Camphor floated in the liquid, or a drop of Oil of Cloves added, will to a great extent prevent it from becoming mouldy by keeping; but if once mould has formed, the bottle must be well cleansed with Nitric Acid, or the decomposition of the fresh Gallic Acid will be hastened. Pour the solution of Gallic Acid into a flat dish, and immerse the Prints two or three at a time, moving them about, and using a glass rod to remove air-bubbles. The development is rapid, and will be completed in three or four minutes. If the Print developes slowly, becomes _very dark in colour_ by continuing the action of the Gallic Acid, but shows no half-tones, it has not been exposed sufficiently long to the light. An over-exposed proof, on the other hand, developes with unusual rapidity, and it is necessary to remove it speedily from the Bath in order to preserve the clearness of the white parts; when taken out to the light, it appears pale and red, with no depth of shadow.