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271tions, will be the same regardless of previous heat-treatment. The data given in Figs. ti and 7 and 11 and 12 for superduty brands A and B, which are of essentially identical composition but have been fired a t about cone 20 and cone 14, respectively, serve best to show that the greatest difference in subsidence between A and B occurred in the early hours of the test, and that the slopes of their subsidence curves later approached each other. Nevertheless, a detailed study of the subsidence data from which these charts were drawn shows that in the last 15 hours of the 100-hour test a t 2400°F., brand B subsided 0.012% per hour, whereas the brick of harder firing, brand A, subsided only 0.006% per hour. There were similar differences at 2500'F. Thus, insofar as this study was carried, it may be concluded that the brick of harder firing exhibited a sustained superiority over the lighter-fired brick.In defense of the existing standard load test, it should be nicntioned that it has provided for the classification of the various types of refractories in a manner that makes possible the desired distinctions, a t least in a broad general way. For some specific service applications, however, a test method with a longer holding period could be used to good advantage. V. ConclusionsData on high-temperature load-bearing characteristics of coinmercial brands of high duty and superduty fire-clay brick have been presented. In performing this work it was found that considerable differences exist between these data and those resulting from other investigations. This can probably be ascribed, in part at least, to the trend toward higher firing temperatures, and possibly, in the case of the other investigations, to the selection of brick not wholly representative of the quality of the type of brick tested.Data also have been presented which are expected to be of value in any consideration of possible modification of the present A.S.T.M. load test.It is not possible to state that a given fire-clay refractory is usable to a given specific temperature, whereas another refractory has a limit of exactly loo0 lower or higher. The nearest approach to this situation, which could well be the hope of all design engineers, is the knowledge, based on data such as have been presented here, that a given brand or type of refractory will show less subsidence and a lower rate of subsidence a t the temperature in question than will another type. More often i t will be found that since the refractory will be heated from only one face, properties other than loadbearing ability will be of greater importance in making the proper selection.The oxidation of Tic-base cermets can be minimized if two processes are stopped : (1) diffusion of oxygen into the cermet body and (2) diffusion of cermet components through the oxide to the oxide-air interface. Two methods of curtailing these diffusion processes are considered : (1) the formation of a n amorphous glassy oxide and (2) the formation of oxidation products which enable certain types of crystalline oxi...

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A new family of sources for vacuum evaporation has been developed for the deposition of pinhole-free films of insulators, semiconductors, and conductors. These sources make use of the fact that a flat plate will scatter particles of molecular size in all directions while reflecting macroscopic particles specularly. This directional separation makes it possible to divert the macroscopic particles away from the substrate. Homogeneous, pinhole-free films can be deposited with these sources at relatively high evaporation rates at close source-to-substrate distances. The use of these sources leads to reproducible films on a high yield basis. The same principle can be used in other applications requiring the filtering of vapors.