Water-bath developers

Water bath development is similar to divided development. Both methods are useful for reducing overall contrast while maintaining density in the key shadow areas. 

There are two major differences between divided and water bath development. The first is agitation. In divided development, agitation takes place in both the first and second baths. In water bath development, the film is gently placed into the second bath and left without motion for two to three minutes. 

The second difference is that divided development is a once-in, once-out process once in A, once in B, rinse, then fix. Water bath development is meant to be a repeatable process. After immersion in the second bath, the film is returned to the A bath and the process repeated as many times as necessary to achieve the desired contrast or density. For this reason, water bath development is best used in conjunction with development by inspection. 

A problem sometimes experienced when using water bath development with conventional and modern emulsions is streaking, which can ruin the film. It may be possible to eliminate the problem by using a 3% sodium sulfite solution (3.0 grams sulfite to 100.0ml of water) in place of plain water in the second bath. This will create somewhat less compensation, but it is better than ruining the negative. 

Technique of Water Bath Development The overall method for water bath development is to immerse the film in the developer for two to three minutes with continuous agitation in a tray. The film is then moved to the plain water or 3% sodium sulfite bath. It should be completely immersed in the water bath and left motionless for two to three minutes then moved back to the developer. The entire procedure is repeated as many times as necessary using a green safelight with a 15-watt bulb to check the progress of development. Turn the light on briefly after each immersion in the water bath and hold the negative up to it at a distance of three to four feet for 20 seconds or less. 

Nonetheless, there are still a few valid reasons to learn how to develop by inspection. The most important is that it allows complete and total control over every image. A second reason is that it might help save negatives when there is doubt as to the correctness of exposure. A third reason is that when developing films by the water bath method to control contrast it is often desirable to visibly monitor development (Chapter 4 Film Development Water Bath Development). The fourth, and final reason, is there may come a time when film will again be hand-coated with loose tolerances. 

Dissolve 5 g. of aniline hydrochloride in 120 ml. of hot water contained in a 200 ml. conical flask and then add 4 g. of potassium cyanate. Heat the solution on a water-bath for 30 minutes, adding about 1-2 g. of animal charcoal towards the end of the heating if a slight turbidity has developed. Now bring the solution quickly to the boil over a gauze, and filter it at the pump, using a Buchner funnel and flask which have been preheated by the filtration of some boiling distilled water. The clear... 

Dissolve 5 g. of benzii in 15 ml. of boiling ethanol in a conical flask fitted with a reflux water-condenser. Then add a solution of 5 g. of potassium hydroxide in 10 ml. of water, and heat the mixture (which rapidly develops a purple colour) on a boiling water-bath for about 15 minutes. Cool and stir the solution, from which the potassium benzii ate separates in fine cr> stals. 

Dissolve 1 g. of the secondary amine in 3-5 ml. of dilute hydrochloric acid or of alcohol (in the latter case, add 1 ml. of concentrated hydrochloric acid). Cool to about 5° and add 4-5 ml. of 10 per cent, sodium nitrite solution, and allow to stand for 5 minutes. Add 10 ml. of water, transfer to a small separatory funnel and extract the oil with about 20 ml. of ether. Wash the ethereal extract successively with water, dilute sodium hydroxide solution and water. Remove the ether on a previously warmed water bath no flames should be present in the vicinity. Apply Liebermann s nitroso reaction to the residual oil or solid thus. Place 1 drop or 0 01-0 02 g. of the nitroso compovmd in a dry test-tube, add 0 05 g. of phenol and warm together for 20 seconds cool, and add 1 ml. of concentrated sulphuric acid. An intense green (or greenish-blue) colouration will be developed, which changes to pale red upon pouring into 30-50 ml. of cold water the colour becomes deep blue or green upon adding excess of sodium hydroxide solution. 

In a 250 ml. conical flask mix a solution of 14 g. of sodium hydroxide in 40 ml. of water and 21 g. (20 ml.) of pure benzaldehyde (Section IV,115). Add 15 g. of hydroxylamine hydrochloride in small portions, and shake the mixture continually (mechanical stirring may be employed with advantage). Some heat is developed and the benzaldehyde eventually disappears. Upon coohiig, a crystalline mass of the sodium derivative separates out. Add sufficient water to form a clear solution, and pass carbon dioxide into the solution until saturated. A colourless emulsion of the a or syn-aldoxime separates. Extract the oxime with ether, dry the extract over anhydrous magnesium or sodium sulphate, and remove the ether on a water bath. Distil the residue under diminished pressure (Fig. 11,20, 1). Collect the pure syn-benzaldoxime (a-benzald-oxime) at 122-124°/12 mm. this gradually solidifies on cooling in ice and melts at 35°. The yield is 12 g. 

The fabric is desized after the weaving operation and then passed through a heated water bath to remove all the size. The rate at which this operation can be accompHshed depends to a great degree on solubiUty rate of the poly(vinyl alcohol). Difficulties encountered in completely removing the lubricating wax, usually tallow wax, has led to the development of several wax-free size compositions (303—311). The main component contained in these blends is PVA in combination with a small amount of a synthetic water-soluble lubricant. 

Scale-Up Fermenters ranging from about two to over 100 hters (0.07-3.5 fP) have been used for research and development, but the smaller sizes provide too httle volume for sampling and are difficult to replicate, whue large vessels are expensive and use too much medium. Autoclavable small fermenters that are placed in a water bath for temperature control are less expensive than vessels with jackets or coils, but much labor is required for handling them. Pressure vessels that... 

Atropine causes dilation of the pupil of the eye. A drop or two of an aqueous solution, containing 1 part in 130,000 parts of water, introduced into the eye of a cat is sufficient to produce this effect. When warmed with sulphuric acid and a small crystal of potassium dichromate, atropine develops a bitter almond odour. Evaporated to dryness on a water-bath with concentrated nitric acid, it gives a residue which becomes violet on adding a drop of sodium hydroxide solution in alcohol (Vitali s test). With a solution of mercuric chloride atropine gives a yellow to red precipitate of mercuric oxide. 

At the end of this period, this 600-ml volume was used as an inoculum for ten liters of the same glucose-corn steep liquor medium which in addition contained 10 ml of an antifoam (a mixture of lard oil and octadecanol). The fermentor was placed into the water bath, adjusted to 28°C, and the contents stirred (300 rpm) and aerated (0.5 liter air/10 liters beer). After 17 hours of incubation, when a good growth developed and the acidity rose to pH 6.7, 2 g of 6a-methylhydrocortisone plus 1 g of 3-ketobisnor-4-cholen-22-al, dissolved in 115 ml of dimethylformamide, was added and the incubation (conversion) carried out at the same temperature and aeration for 24 hours (final pH 7.9). 

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