Decembcr, 1924
INDUSTRIAL A N D ENGILVEERINGCHEMISTRY
sidered, but the apparatus had to be arranged so that it would deal efficiently with gas containing tarry matter and naphthalene, which would clog many types of packing. I n fact, a good deal has come to be expected of this liquid purification process in addition to the simple removal of hydrogen sulfide, and it is usually demanded that the apparatus be a gas cooler, a naphthalene washer, a tar extractor, a cyanide washer, and a sulfur remover all in one. Three principal types of packing have been ued-viz., coke, wooden hurdles, and spiral tile. Coke (0.5 to 1 inch size), if carefully screened, gives good results with gas free from suspended matter and is the cheapest of the three. However, it is much more subject to trouble on account of stoppage with dirty gas. Both wooden hurdles and spiral tile are very satisfactory from the standpoint of efficiency and have given excellent results under a variety of conditions. One plant, recently put into operation, has steel turnings as packing material and is giving very satisfactory results.
EFFICIESCY OF PROCESS In all the liquid purification plants thus far installed, the process operates to remove 85 to 90 per cent of the hydrogen sulfide, the remainder being taken out in the oxide purifiers. In this way the latter are used as catch boxes and the investment in them is not lobt. The insta1lat)ion of a liquid purification plant has the effect of increasing the capacity of the oxide boxes two and a half times and makes it unnecessary to renew the oxide except after intervals of many months. It often happens that the amount of purifying capacity is the limiting factor in the growth of a plant on any particular site. In such cases, with dry purification an increase of capacity can only be obtained by building a new plant on another site, while with liquid purification the capacity of a plant on a given sito can be more than doubled. With such an installation the system is able to deal with great fluctuations in the hydrogen sulfide content of the gas. The liquid purification process absorbs such fluctuations, since it is able to treat gas of 1000 grains hydrogen sulfide per 100 cubic feet just as readily and even more efficiently than gas of 100 grains per 100 cubic feet. Thus, the catch boxes are only required to deal with comparatively small amounts and minor fluctuations. The process can also be adapted for complete removal of hydrogen sulfide, and developments are now under way which are expected to make possible the recovery of the sulfur in the hydrogen sulfide.
Bureau of Standards Annual Report Scientific investigations and tests resulting in large savings to the Government and to American industry through improvement in processes and the fixing of uniform standards are featured in the annual report of George K. Burgess, director of the Bureau of Standards. Investigations made with orifice meters for measuring gas, corrosion of underground pipes, and tests conducted covering impact stresses in highway bridges, braking systems for automobiles, and other studies, have resulted in the application of improved methods in engineering practices that are of direct and substantial savings to the industrial public. Other contributions to the public interest are the successful development of methods of reducing the loss in the baking of Japan ware, the assistance rendered the optical glass industry in the United States, the progress made in the better utilization of cotton linl ers and other cotton wastes, and the development of a method for reclamation of gasoline from dry-cleaning processes. An increase of more than one hundred and twenty five times its initial volume has taken place in the testing work of the Bureau of Standards during the twenty-three years of its existence. During the year just closed 135,852 tests were conducted by all divisions of the Bureau, as compared with 115,729 in 1923. Most of the tests were executed for other branches of the Government, but a great deal of testing was also done for commercial firms and individuals. Unfortunately, some of this latter work had to be refused because the demand exceeded the facilities. The inability to meet this demand is unfortunate.
1239
Quantitative Analysis of Mists and Fogs, Especially Acid Mists' By Harold C. Weber MASSACHUSETTS INSTITUTE OF TSCHNOLOGY, CAMBRIDGE, MASS.
T
HIS paper is presented, not because it contains any new
methods of analysis, but rather to describe in detail the methods that the author has found successful for the determination of mists, especially sulfuric acid mists, in the plant. Such a paper has a place in an absorption symposium, for much of the published work on absorption is unreliable, because the methods of gas analysis involved completely ignore the necessity of analyzing for any mist that may be present. There can be no doubt that many of the irregularities in absorption data, especially where these data concern the absorption of acid gases, can be satisfactorily explained by the assumption that a mist was present during the analytical absorption. A mist or fog is made up of small particles of varying sizes. These particles may be either liquid or solid. One concept is that each individual particle is surrounded by an air film which effectively insulates it from its neighbors. According to this idea, then, any method of analysis to be effective must present some means of breaking through this air film. It is possible, however, to explain practically all the peculiarities associated with mist analysis and absorption without assuming the existence of' this protective air film. If we assume that the mist particles are so small that they do not settle out readily by gravity and that they are so large that their rate of diffusion is extremely small compared with the diffusion rate for gases, it is possible to see that extreme difficulty would be experienced in dissolving them. From this discussion it is evident that any method of analysis which proposes to analyze for mist by the mere bubbling of the gas through an absorbing medium should be looked upon with distrust. After a careful search of the whole field two fundamentally different methods of analysis were selected as possibilities. The first of these consists of passing the gas containing the mist through some type of porous membrane in which the pores are sufficiently small so that the mist particles are effectively trapped. Whether this trapping occurs by an actual scraping aside of the protecting gas film, whether it is due to the throwing out of particles as they pass through the torturous passages of the porous medium, or whether it is due to some other cause will not be discussed a t this point. The second method which presented itself was an adaptation of the principle involved in the Cottrell precipitator to a small portable apparatus for use in the plant.
POROUS MEMBRANE METHOD Several types of porous membrane apparatus were tried out, but only three of them gave satisfactory service; and of the three only two were finally retained. The first method tried was that involving the use of an asbestos mat. This mat was formed by catching a suspension of long-fibered asbestos on an ordinary 4-inch porcelain Buchner funnel. The preparation of these mats is rather difficult and the subsequent drying which must be done before the mat can be used is especially difficult. Cracks are very liable to form slightly below the asbestos surface. These cracks may be entirely invisible to the eye, but nevertheless they allow mists to pass through. The funnels themselves are clumsy to handle, and owing to Presented under the title "The Quantitative Determination of Mists and Smokes wlth Special Reference to the Determination of Sulfur Trioxide Mists."
