8 Transactions of the South African Philosophical Society. 



abuse. We are gravely told — generally by persons who are neither 

 chemists nor have kept abreast of the times in scientific agriculture 

 — that soil analysis has not the value for the farmer once attributed 

 to it. But there is a flaw in the reasoning, owing to want of defini- 

 tion : logicians call it the fallacy of the ambiguous middle term. We 

 may put the syllogism in another way, and you will then perceive 

 the flaw at once : Some modes of soil analysis are valueless for agri- 

 cultural purposes ; the determination of the proportion of plant food 

 in the soil is one mode of soil analysis ; hence the determination of 

 the proportion of plant food in the soil is valueless for agricultural 

 purposes. Here the substantial correctness of both major and minor 

 premises may be conceded, but the conclusion is false ; it is the 

 fallacy of a universal conclusion from a particular premise. It is 

 by people who reason in this manner that chemists who perform 

 and Governments who permit extensive investigations into the 

 nature of the country's soils for the benefit of the agriculturist 

 are held up to fine scorn for squandering the taxpayers' money in 

 vain research. 



There is, however, an opposite extreme. This, like the last, is 

 common to the learned and the unlearned. Many imagine that the 

 chemical analysis of a thimbleful of soil will terminate all agricul- 

 tural perplexities for the farmer. Both extremes are erroneous, and 

 for one reason : the exact nature and scope of agricultural chemical 

 analyses of soils are not properly understood. 



It is a generally accepted fact that certain chemical compounds 

 are necessary to the normal growth and development of plants. 

 Most prominent amongst these compounds are lime, potash, and 

 phosphoric oxide. These three comprise the inorganic or mineral 

 constituents of the food of plants ; there are other constituents as 

 well, but it is not material to refer to these here. The three com- 

 pounds just named are therefore termed " plant-food constituents." 

 It is essential and important to note the distinction between " plant- 

 food constituents " and '' plant food^' Potash, for instance, is a 

 plant-food constituent, no matter where or how it may exist, w^hether 

 deep down in the mines of Stassfurt, or in the wool on the sheep's 

 back ; in the impermeable granite below Table Mountain or in the 

 waters of the Dead Sea ; but it is not plant food except when present 

 in the soil ; more than that — except when present there in the very 

 condition in which the plant growing upon that soil can withdraw it 

 and turn it to its own account. 



Now a chemical analysis of the soil, to be of value to the farming 

 community, should tell — not the quantities of plant-food constituents 

 present, but the proportions of plant food. It becomes obvious. 



