protosulphateprotosulfaten.
/ˌprəʊtə(ʊ)ˈsʌlfeɪt/, U.S. /ˌproʊdoʊˈsəlˌfeɪt/ Chemistry. Now rare.
A sulphate in which the sulphate anion occurs in its smallest possible proportion relative to the other element (i.e. one in which the other element occurs in its lowest oxidation state). Cf. proto- comb. form 3a(b), persulphate n.
ΚΠ
1819 J. G. Children Ess. Chem. Anal. 430 Sulphuretted hydrogen destroys the colour of the red compound of strychnine, as does..protosulphate of iron.
c1865 J. Wylde Circle of Sci. I. 146/1 Protosulphate of iron is well known under the name of green copperas.
1913 H. J. Wheeler Manures & Fertilizers xxiv. 352 In better aërated bogs, also, toxic iron protosulfate (FeSO4 + Aq.) may be formed by the oxidation of iron sulfid.
1955 H. Gernsheim & A. Gernsheim Hist. Photogr. iii. xi. 124 The exposure was only half a minute and the picture was developed with protosulphate of iron.
This entry has been updated (OED Third Edition, September 2007; most recently modified version published online March 2022).
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n.1819