1909, from German PH, introduced by S.P.L. Sörensen, from P, for German Potenz "potency, power" + H, symbol for the hydrogen ion that determines acidity or alkalinity.
ph
now in English usually representing "f," originally it was the combination used by Romans to represent Greek letter phi (cognate with Sanskrit -bh-, Germanic -b-), which at first was an aspirated "p," later the same sound as German -pf-. But by 2c. B.C.E. had become a simple sound made by blowing through the lips (bilabial spirant).
Roman "f," like modern English "f," was dentilabial; by c. 400, however, the sounds had become identical and in some Romanic languages (Italian, Spanish), -ph- regularly was replaced by -f-. This tendency took hold in Old French and Middle English, but with the revival of classical learning the words subsequently were altered back to -ph- (except fancy and fantastic), and due to zealousness in this some non-Greek words in -f- began to appear confusedly in -ph-, though these forms generally have not survived.
双语例句
1. Skin is naturally slightly acidic and has a pH of 5.5.
皮肤具有天然弱酸性，pH值为5.5。
来自柯林斯例句
2. A pH test measures the acidity or alkalinity of a substance.
pH值测试可检测物质的酸碱度。
来自柯林斯例句
3. a pH of 7.5
pH值7.5
来自《权威词典》
4. The fluid that emerges from the vents is acidic (pH 3) and hot.
从那些出口出来的液体呈酸性（pH值为3），且是热的。
来自柯林斯例句
5. pH is a measure of the concentration of free hydrogen atoms in a solution.