Fumes, stop baths

Adequate ventilation in the darkroom will eliminate acid fumes. The photographer should wear goggles, an apron, and plastic gloves, and should use tongs when handling negatives and prints in a stop bath. 

The fumes which emanate from acetic acid stop baths are perhaps the single greatest health hazard in the darkroom. Over time, these fumes can cause damage to the delicate membrane of the sinuses, resulting in respiratory problems. For this there are also two solutions. 

HC1 is introduced at 0 C into a stirred mixture of ethanol (0.50 mol) and paraformaldehyde (15 g) until copious fumes escape from the solution. Stirring is stopped and the flask is placed in a bath at -78 C. The clear liquid is decanted from the crust of the bottom of the flask and transferred into a 1 -1 flask, which is placed in a bath at -20 C. The dissolved HC1 is then removed by evacuation (water aspirator). Since a-halocthers are suspected of being carcinogens, care should be taken when working with them. 

Caseous hydrogen chloride (2 to 31/rnin) is introduced into a mixture of 1.0 mol of propargyl alcohol (freshly distilled under reduced pressure) and 0.33 mol of paraldehyde, while keeping the temperature between -15 and -5 C. The introduction of gas is stopped when copious fumes escape from the outlet. The auxiliary equipment is removed and the flask allowed to stand for several min in a bath at -70 C. After solidification of the lower layer (concentrated aqueous HCl), the upper layer is cautiously decanted from the ice mass and vigorously... 

Liquid Bfj (0.5 mL, 10 mmol, fourfold excess) is added to the yellow or pale green solution, and Nj immediately begins to evolve from the interface of the Bt2 and CF3SO3H layers. The pale green color that is sometimes observed results from an impurity of the mixed-valence species [(NHjlsOsNjOsfNHj) ] , but under the reaction conditions this compound is also oxidized to the [0s(NH3)j(0S02CF3)] ion. ( Caution. Bromine is toxic and corrosive. Avoid contact with the skin and eyes. The reaction should be carried out in a well-ventilated hood.) A constant flow of Nj or Ar is commenced in order to stir the solution while the temperature is maintained around the boiling point of Brj, 50-60 . The gas flow is stopped periodically to determine if the evolution of Nj gas has ceased from the interface of the two layers. When the evolution has ceased (—0.5-1 hr), the solution is heated to 110° in an oil bath, and a constant gas flow is maintained in order to drive off excess Brj and the HBr that has been produced in the reaction. ( Caution. Bromine and HBr are both corrosive and toxic.) After the brown fumes have ceased and no Brj remains in the bottom of the flask, the solution is cooled to room temperature and is then cooled in an ice bath to <5°. Anhydrous diethyl ether (—30 mL) is added dropwise to the rapidly stirred solution. 

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