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described as a method for preparing only nitrosoguanidine. The systems nitro/nitrosoguanidine and nitroso/aminoguanidine are very good examples of organic reversible systems and have been extensively studied (Smith and Sabetta, 1932).Large-Scale Experiments. The reduction was then studied after scaling up the cells to 300-A capacity. The 300-A cell consists of a PVC tank (80 X 30 X 36 cm) havingfour porous pots (10-cm diameter X 50-cm height. Two araldite coated stainless steel coils are used to cool the catholyte. The cathodes were three cylinders of mild steel on which zinc was deposited from a sodium zincate bath using zinc anodes (10 cm in diameter X 30 cm long with an effective area of 9.0 dm2). The anodes were perforated cylindrical lead sheets.The results of the large-scale experiments are given in Table V.Further experiments are in progress to study the reuse of the electrolyte and recovery by the addition of ammonium bicarbonate.

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New data have been obtained on vaporization of water from rippling and nonrippling films in a countercurrent wetted-wall tower. Other similar data in the literature have been analyzed, and an effect of liquid Reynolds number on gos phase mass transfer has been shown to exist. Discrepancies in much of the literature data can be explained on this basis.The data on vaporization of water from rippling films have been correlated. The data on nonrippling films were correlated when the gas Reynolds number was calculated relative to the water surface.Attempts to correlate data on vaporization of pure liquids in a wetted-wall tower brought to attention various discrepancies in the available literature. Data obtained in this laboratory on vaporization of water into air flowing countercurrently indicated that the gas phase mass transfer coefficient was affected by liquid flow rate. In most pre- indicated that liquid flow conditions affect surface area and gas phase pressure drop and therefore might be expected to influence the gas mass transfer process.Hydrodynamic studies related to wetted-wall columns are well summa- Theoretical derivations (7, 2 2 ) , predict a ratio of 1.5 for surface velocity to average velocity when the liquid film is in true laminar flow with no gas flow. Jackson, Johnson, and Ceaglske The first comprehensive study of vaporization in a wetted-wall tower was made by Gilliland and Sherwood ( 1 2 ) who obtained data on both parallel and counterflow vaporization. Although the volumetric flow rate of the liquid was maintained approximately constant in all of this work and was well into the rippling range for the various liquids, the N R~~ varied considerably owing to differences in viscosity and density. In correlating their data Gilliland and Shenvood found a dependence on the direction of gas flow when N ' R~~ was used. However when gas Reynolds number calculated relative to the pipe wall was used, both parallel and counterflow data could be represented by the same correlation. This was the basis for the use of N R e g by later workers correlating this type of data.An

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