A manual of photographic chemistry, including the practice of the collodion process

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Page 62 - In exemplifying further the importance of distinguishing between visual and actinic rays of light, we may observe, that, if the two were in all respects the same, photography must cease to exist as an art. It would be impossible to make use of the more sensitive chemical preparations, from the difficulties which would attend the previous preparation and subsequent development of the plates. These operations are now conducted in what is termed a dark room ; but it is dark only in a photographic sense,...
Page 61 - The actinic and luminous rays are totally distinct from each other, and the word "photography", which signifies the process of taking pictures by light, is in reality inaccurate.' And, again (page 62), 'In exemplifying further the importance of distinguishing between visual and actinic rays of light, we may observe, that, if the two were in all respects the same, photography must cease to exist as an art. It would be impossible to make use of the more sensitive chemical preparations...
Page 188 - Ata temperature of 58' to 60Э. specific gravity l'S33 is about the nsusl strength, and if it falls below this, it will be better to reject it. " The nitre should be the purest sample which can be obtained. Commercial nitre often contains a large quantity of chloride of potassium, detected on dissolving the nitre in distilled water, and adding a drop or two of solution of nitrate of silver. If a milkiness and subsequent curdy deposit is formed, chlorides are present. " These chlorides are injurious...
Page 369 - Take the pure crystallized chloride of sodium, — which operative chemists make purposely for analysis by dissolving the best carbonate of soda in pure hydrochloric acid. — and either dry it strongly or fuse it at a moderate heat, in order to drive off any water which may be retained between the interstices of the crystals ; then dissolve in distilled water, in the proportion of 8^ grains to 6 fluid ounces.
Page 248 - Fixing and Toning Bath with Chloride of Gold. — Dissolve four ounces hyposulphite of soda in four ounces of water, solution of chloride of gold, a quantity equivalent to four grains, in three ounces of water; thirty grains nitrate of silver in one ounce. Pour the diluted chloride by degrees into the hyposulphite, stirring with a glass rod ; and afterwards the nitrate of silver in the same way. This order of mixing the solutions is to be strictly observed ; if it were reversed, the hyposulphite...
Page 250 - ... be required. The time of exposure to light varies much with the density of the Negative and the power of the actinic rays, as influenced by the season of the year and other obvious considerations. As a general rule, the best Negatives print slowly; whereas Negatives which have been under-exposed and under-developed print more quickly.
Page 251 - ... prepared with iodine or perchloride of iron, dissolves away the lighter shades more than the neutral bath, with chloride of gold. When the proofs are to be immersed for a, long time in order to secure black tones, it is necessary to over-print more strongly" than when the purple tints are desired. If, on removal from the printing-frame, a peculiar spotted appearance is seen, produced by unequal darkening of the chloride of silver, either the nitrate bath is too weak, the sheet removed from its...
Page 38 - ... on these spots differently to what it does on the other untouched parts." To illustrate this, take a thin plate of metal, having characters excised; warm it gently, and lay it upon the surface of a clean mirror glass for a few minutes : then remove, allow to cool, and breathe upon the glass, when the outlines of the device will be distinctly seen.
Page 245 - Sensitizing is by means of Ammonio-nitrate of Silver, sixty grains to the ounce of distilled water, prepared thus : — Dissolve the Silver in one-half of the total quantity of water. Then take a strong solution of Ammonia and drop it in carefully, stirring meanwhile with a glass rod. A brown precipitate of Oxide of Silver first forms, but on the addition of more Ammonia it is redissolved. When the liquid appears to be clearing up, add the Ammonia very cautiously, so as not to have excess. In order...
Page 327 - ... slightly alkaline reaction to test-paper ; it is somewhat thick and glutinous, but becomes more fluid on the addition of a small quantity of an alkali, such as Potash or Ammonia. Soluble Albumen may be converted into the insoluble form in the following ways : — 1. By the Application of Heat. — A moderately strong solution of Albumen becomes opalescent and coagulates on being heated to about 150 Fahrenheit, but a temperature of 212 is required if the liquid is very dilute.

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