388 Scientific Proceedings, Royal Dublin Society. 



Nomenclature of soils with respect to acidity and alkalinity. 



Wherry, in dealing with plant distribution in relation to the hydrogen 

 ion concentration of the soil, felt the need of some verbal expression other 

 than quoting pH limits. He accordingly (1919) proposed a convenient 

 terminology which will be used in places in the account of such work which 

 follows, but the pH limits by which they are defined should always be borne 

 in mind. Thus from pH 7-6 is denoted as minimacid, 6-5 as subacid, 5-4 as 

 mediacid, less than pH 4 as superacid. Corresponding terms are used in the 

 alkaline range. This nomenclature is not entirely free from objection, 

 especially on the alkaline side, as there is reason to believe that pH 9-0 up 

 to 9'2, or possibly more, is not as a general rule harmful to plants and certain 

 protozoa, while it is exremely likely that pH 9'7 and over is decidedly 

 injurious to all plant life; yet both are classed as medialkaline, and only at 

 pH 10 is superalkaline reached. Wherry also drew attention to the fact 

 that pH values were not understood by many biologists, and suggested the 

 use of such terms as specific acidity and specific alkalinity, taking the 

 hydrogen and hydroxyl ion concentration of pure water as one. Thus pH 6 

 is of specific acidity 10, pH5'5 approximately 30 — in reality it is 32 — and is 

 given by Wherry as .30 +. Correspondingly on the alkaline side, pH 9 is 

 equivalent to specific alkalinity 100. To the writer these specific values 

 appear to be unnecessary, and to destroy the unity of the one scale, the 

 pH value, which covers all ranges of chemical and biological reaction. Thus, 

 if figures are given, they will be pH values, as is strongly advocated by 

 Clark (1920). 



In addition to the terms already given. Wherry embraces the region from 

 pH 6-8 in the term circumneutral. In this limit he places leaf mould, whilst 

 bog peat is from pH 6 to 4 approximately, and "alkali" soil from pH S upwards. 

 Upland peat is given as pH 5-7, and limestone soil as 7-9. Fischer (1914), 

 by the electrical method, found for " Hochmoor " sphagnum pH 3'02-3'19, 

 and for "Flachmoor " soil and plant debris pH 5'22-5'95. 



A proposal similar to Wherry's was made by Walker and Kay (1912) 

 some years previously for recording the alkalinity (or acidity) of water in 

 terms of specific values, taking pure water at the same temperature as unity. 

 This was made before the use of the pH symbol became general. 



Halation of the hydrogen ion concentration of soil to geological formation 



originating it. 



It is obvious that when a soil has been transported so as to lie over strata 

 of different composition from those from which it originated, there can be no 

 relation between the acidity or alkalinity of the soil and rock strata. 



G 



