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blistering of sheet metal, embrittlement during pickling, and the hardness and brittleness of electrolytic iron, but most of these troubles were ascribed to an "excess" of hydrogen. However, recent experience in the hot working of metals has shown that hydrogen furnishes an outstanding example of the disastrous effects that may result from the presence of surprisingly small amounts of impurities in metals.
Less than 0.001 per cent. of hydrogen is believed to be responsible for the defects known as "flakes" in forging steels and as "shatter cracks" in railroad rails.
The available methods for determining minute amounts of hydrogen in steel are discussed in a paper (RP1373) by Vernon C. F. Holm and John G. Thompson which will be published in the Journal of' Research for March.
The authors found that a method wh;ch involves vacuum extraction of the hydrogen at 800' C. is rapid and yields reliable results for a variety of materials.
Prompt sampling and immediate analysis are advisable because many samples lose hydrogen during storage, even at room temperature.
;\lloy steels with high chromium contents dissolve more hydrogen and retain it more tenaciously than do simple steels.
Hot rolled rods of low-carbon steel, some time after they were rolled, had low and uniform contents with no evidence of segregation of the hydrogen.
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