The U.S. gold stock was $4,356 million in January 1931. It rose to $4,708 million in August and then fell $4,173 million in December 1931.
Here are the figures:
January 1931 – $4,356 million
January 1932 – $4,129 million
January 1933 – $4,265 million
January 1934 – $4,033 million
The data is in Table No. 156, page 537:
http://fraser.stlouisfed.org/docs/publications/bms/1914-1941/section14.pdf
After the gold stock was revalued at $35 an ounce in February 1934, the figures are:
February 1934 – $7,438 million
January 1935 – $8,391 million
January 1936 – $10,182 million
January 1937 – $11,538 million
January 1938 – $12,756 million
January 1939 – $14,682 million
January 1940 – $17,931 million
The argument is that the outflow of gold was bad for the European countries because, under the rules of the classic gold standard (which as pointed out already didn’t exist after WWI), it would have forced them to deflate their money stocks leading to price deflation. Allegedly this deflationary effect was not counter-balanced by an inflation in the U.S. because the Treasury was sterilizing the gold inflow, i.e., offsetting the additional gold with a decline in other forms of money.
But the gold sterilization program of the Treasury did not occur until 1937: