Specks of silver

This process continues until a small speck of silver is created. It is these clusters of silver that absorb the light falling on the glass. The absorption characteristics of the silver specks depend quite critically upon their size and shape. Photochromic glass production is carefully controlled so as to produce a wide variety of shapes and sizes of the silver specks, ensuring that the glass darkens uniformly. 

So, with the help of a chemist friend, you gain access to the most powerful microscope in the world, and you continue the cutting and discarding process. Finally, you get to the point at which you can absolutely go no further. At that point, you have a speck of silver barely visible through this most powerful microscope. The question in your mind is, how far would I be able to go if I could go farther And so you start to dream and imagine that you have access to a microscope so powerful that you can see the tiniest objects that can possibly exist. 

Fig. 13. A speck of developing sdvei on the surface of a sdvei hahde crystal. The silver acts as an electrode for the electrochemical reduction of silver ions.

Both reduction centers and latent image centers are composed of silver, and to Moisar "it seems safe to assume that the silver specks formed by reduction are identical to those which somehow appear as subspecks and alleged intermediate entities during photolytic silver formation" (93). He proposed that Ag2 centers formed by exposure by light can act as hole traps and Agj centers act as subdevelopable precursors of latent image centers but, as Hamilton and Baetzold comment (96),... 

Since there is an enormous density of such equivalent sites on the surface of a silver halide microcrystal, it would be surprising if a single speck of Ag2S were formed on each grain even under optimum conditions of sulfur sensitization. The sensitizer forms an adsorption silver complex which reacts to form an adsorbed molecule of Ag2S. 

Spot test To 1 drop of the test solution add 1 drop nitric acid (2m), then 1 drop of the reagent. A red-violet precipitate or stain is formed if silver ions are present. Alternatively, the test may be performed on a spot plate, or in a semimicro test tube in the latter case the excess of the reagent is extracted with diethyl ether or amyl alcohol, when violet specks of the silver complex will be visible under the yellow solvent layer. 

Further work [86] showed that the specific surface free energy of silver particles was the same whether they were evaporated on carbon or silver bromide, but was lowered by coating with gelatin. The latter is given as the reason for the stabilizing effect of gelatin on latent image specks. 

The latent image catalyzes the reduction of silver ion either from the solid silver halide phase, as in chemical development, or from a soluble source of silver ion, as in physical development (Figure 21). One view of chemical development is that interstitial silver ions move through the silver halide crystal and are reduced on the underside of the latent image speck. In purely physical development complexed silver ion moves through the solution and is reduced on the nucleus. In this sense physical development and the early stages of chemical development are similar. 

The spherical growth of the latent image will accelerate because of the increase in surface area and Berry [98] suggested that once the rate reaches a value such that the rate of diffusion of silver atoms on the surface of the growing speck is unable to maintain a spherical shape, silver filaments move out from the grain surface. 

When a photon is absorbed by a silver halide grain, an electron is ejected from a halide ion and temporarily held at some site in the crystal. A silver ion can migrate to the site and combine with the electron to form a silver atom. The atom is not stable it can decompose back into a silver ion and a free electron. However, during its lifetime, the atom can trap a second electron if one becomes available. If this second electron remains trapped tmtil the arrival of a second silver ion, a two-atom cluster forms. This buildup of a silver cluster can continue as long as photoelectrons are available. The smallest cluster corresponding to a stable latent image speck is believed to consist of three or four silver atoms. Specks of this size or greater on the crystal surface can catalyze the subsequent action of a developer. 

According to the method for making Amber Pills from the Golden Liquor, boil the Golden Liquor with quicksilver for thirty days. Fill an earthenware bowl [with the quicksilver] and lute it with the Mud of the Six-and-One. Place it over a raging fire and heat it. In sixty double hours its whole content will transmute itself into an elixir. Ingest this elixir in pills the size of small beans, and you will become an immortal. Take a speck of it with a spatula, add one pound of quicksilver, and it will form silver. Baopu zi, 4-83)... 

If you add yellow clay to the Golden Liquor, place them in a bowl luted with the Mud of the Six-and-One, and heat the bowl over an intense fire, its whole contents will form gold. This is the first half of the procedure. If you heat this gold longer, it will transmute itself into an elixir. By ingesting this elixir in pills of the size of small beans, you will be able to enter a famous mountain or a great river and become an Immortal of Earth (dixian). If you powder a speck of this elixir into quicksilver, it will immediately become silver if you add one ounce of this silver to one pound of lead, it will all become silver. (Baopu zi, 4.83)... 

Fig. 3. Cross-section photomicrograph of a color-negative product showing the film base, the emulsion layer (the black specks are microcrystalline silver hahde grains), and a protective overcoat. The emulsion layer and overcoat are - 3.5 x 10 m thick.

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