428 abstracts: technology 



favorable and which unfavorable for the occurrence of oil, to discourage 

 drilling in the unfavorable localities, and thus to aid those interested 

 in making conclusive tests to determine the presence or absence of oil 

 and gas. 



All the rocks of the area are sedimentary in origin and are relatively 

 young, the exposed rocks ranging in age from Claiborne (Eocene) to 

 Recent. Of these formations the loess and the Jackson underlie by 

 far the greater part of the a r ea, and the Vicksburg and Catahoula 

 formations and the terrace sand and gravel underlie smaller areas. 



The general structure of the Gulf coastal plain is simple. A series 

 of beds slopes gently southward and passes successively deeper and 

 deeper beneath more recent deposits toward the coast. This general 

 dip toward the coast is interrupted by local steepening or flattening 

 and in a few places by a reversal in direction. These irregularities of 

 dip, which are of greatest significance in the accumulation of oil and 

 gas in valuable pools, are well illustrated in the Vicksburg-Jackson 

 area. The geologic structure is represented on a map by contours on 

 the Vicksburg limestone. The possibilities of oil and gas occurring in 

 the area are discussed and the most promising areas for prospecting 

 are pointed out. R. W. S. 



TECHNOLOGY. — The effusion method of determining gas density. 



Junius David Edwards. Bureau of Standards Technologic Paper 



No. 94. Pp. 30. 1917. 

 In cooperation with a number of men employing this method in the 

 natural gas industry a series of experiments was made using their 

 apparatus under field conditions. It was found that results in error 

 by more than 10 per cent were not unusual. The theory of the effusion 

 process was studied, and the effect of differences in physical properties 

 upon the relative rates of effusion of air and hydrogen, argon, methane, 

 and carbon dioxide at different pressures was determined. Also ob- 

 servations were made on the effect of the effusion pressure, the confining 

 medium and the shape and size of the orifice. It is very important 

 that the orifice be of the proper size and shape. It has been shown 

 that the apparent specific gravity, as determined by this method, can 

 be varied within rather wide limits by changing the conditions. How- 

 ever, by the observance of certain precautions in the construction and 

 use of the apparatus, it is possible to secure results accurate to about 2 

 per cent. Recommendations have been made as to the most suitable 

 type and form of apparatus. J. D. E. 



