Chemistry - What is "super" in superphosphate?
Solution 1:
The term superphosphate is really old, even well before the concept of atoms was proposed by Dalton. Therefore it is difficult to rationalize the choice of this terminology.
In the unabridged version of the Oxford English Dictionary, you can see the earliest usage dates back to 1798
Chemistry. A phosphate containing an excess of phosphoric acid; an acid phosphate. Now disused except in superphosphate of lime, calcium superphosphate: cf. sense 2.
1798 Philos. Trans. (Royal Soc.) 88 17 It was..Scheele who discovered, that the urine of healthy persons contains superphosphate, or acidulous phosphate, of lime.
Further information from the OED on the usage of "super" in chemical names confirms its use since antiquity. See antique examples
(b) Denoting the highest proportion of a component, esp. owing to a high oxidation state. Now chiefly archaic or hist., except in superoxide n. and in the names of certain substances used in industry and commerce, as superphosphate n., supersulphate n. Cf. sub- prefix 4b(b). (i) Categories » [1788 J. St. John tr. L. B. Guyton de Morveau et al. Method Chym. Nomencl. 107 New names... Acetite of lead. Ancient names... Sugar of lead, Super-acetated lead.] 1811 Jrnl. Nat. Philos. June 78 The aqua lithargyri acetati is a saturated solution of the proper acetate of lead,..it is an essentially different salt from the super-acetate of lead. 1913 Brit. Med. Jrnl. 4 Oct. 875/1 Dr. Latham..used the superacetate of lead in consumption. 1979 A. J. Youngson Sci. Revol. Victorian Med. i. 18
Acetate or superacetate of lead combined with opium was prescribed for haemorrhage of the lungs.
Solution 2:
Superphosphate is a name used in agriculture, therefore, it does not mean the same super in the superoxides. There are two important types of fertilizers in agriculture: Nitrogenous and phosphatic fertilizers. Superphosphate is an one of major segments in phosphatic fertilizers, which is described as follows (Ref.1):
The primary products of the phosphatic fertilizers industry are phosphoric acid, ammonium phosphate, normal superphosphate, and triple superphosphate. Phosphoric acid is sold as is or is used as an intermediate in producing other phosphatic fertilizers. Monoammonium phosphate is favored for its high phosphorous content, while diammonium phosphate is favored for its high nitrogen content. Normal superphosphate has a relatively low concentration of phosphorous, however it is used in mixtures because of its low cost. Triple superphosphate provides a high concentration of phosphorous, more than 40% phosphorous pentoxide.
Normal or ordinary superphosphate fertilizers (NSP) are produced by reacting phosphate rocks with sulfuric acid (for this reason, NSP retains its importance in wherever sulfur efficiency limits crop yields). Normal orsuperphosphate fertilizers are refer to the fertilizer material containing 15-21% phosphorus as phosphorus pentoxide ($\ce{P2O5}$). NSP contains no more than 22% of available $\ce{P2O5}$ (Ref.1).
Triple superphosphate fertilizers (TSP) are produced by reacting ground phosphate rocks with phosphoric acid. Triple orsuperphosphate fertilizers are also known as double, treple, or concentrated superphosphate. The phosphorus content of TSP is over 40% measured as phosphorus pentoxide ($\ce{P2O5}$), which is its major advantage over other phosphatic fertilizers (Ref.1).
Note: To my knowledge, there are no other names such as supernitrates in fertilizer industry or agriculture, to tell the least.
References:
- Nicholas P Cheremisinoff, Paul E. Rosenfeld, "Chapter 1: Industry and Products," Handbook of Pollution Prevention and Cleaner Production, Vol. 3: Best Practices in the Agrochemical Industry; 1st Edn.; Elsevier Inc.: Oxford, United Kingdom, 2011, pp. 1-24 (https://doi.org/10.1016/B978-1-4377-7825-0.00001-7).
Solution 3:
"Super" in "superphsophate" probably refers to it being super-active, with its phosphorous more readily available than it would be in an ordinary phosphate. Chemically this is done by combining calcium phosphate with sulfuric acid giving an acid salt that is more soluble than normal-salt calcium phosphate would be. See here, for example.
Superoxide is not a analogous to superphosphate. It is, as the OP may know, $\ce{O_2^-}$ instead of the normal oxide ion $\ce{O^{2^-}}$. In simple salts it's stable only with alkali metal cations, but oxyhemoglobin has been considered as a superoxide complex.
I am not aware of any "super" ions other than superoxide, as superphosphate is just a catchy name for acid-sslt phosphates (see #1). Feel free to edit with any corrections.