These Data Were Interpolated By Discountinuous Sample (First And Fourth Quarters). See The Source For A More Complete Description. Source: Harold Barger, Outlay And Income In The United States: 1921-1938, Table 28.
This NBER data series q09025a appears on the NBER website in Chapter 9 at http://www.nber.org/databases/macrohistory/contents/chapter09.html.
NBER Indicator: q09025a
Release: NBER Macrohistory Database
National Bureau of Economic Research, Net Profit of Mining Corporations for United States [Q0925AUSQ144SNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/Q0925AUSQ144SNBR/, August 31, 2015.