SOOT is that portion of fuel which escapes combustion, and which is mechanically carried up and deposited partly in chimneys and partly in the air. The soot of coal and that of wood differ very materially in their composition ; the former indeed does not appear to have been accurately analysed, but it evidently contains more carbonaceous matter than the latter. Coal-soot contains substances usually derived from the distillation of organic matters ; it contains sulphate and hydrochlorate of ammonia, and has been used for the preparation of the carbonate ; to hot water it yields a brown bitter extract, and it contains an empyreumatic oil ' • but its great basis is charcoal in a state in which it is capable of absorbing ammonia from the air, and hence with the ammoniacal salts it already contains, it is used as a manure, and acts very powerfully as such. Sir H. Davy observes that for this purpose it is well fitted to be used in the dry state, thrown into the ground with the seed, and requires no preparation.
The soot of wood has been minutely analysed by Braconnot, who found it to consist of the following substances :— Braconnot considers the ulmin as absolutely similar to that obtained artificially by the action of potash on wood-sawdust, but Berzelius is of a different opinion, and calls it gein. The azotised matter is very soluble in water, and insoluble in alcohol. As coal-soot contains much more carbonaceous matter than wood-soot, and also a much larger portion of ammoniacal salts, it must be more active as a manure, and altogether a more useful substance.
SOPHISM (16˘sosca), that superficial and incomplete aspect of the truth, which at first sight looks like the truth, but on closer inspection turns out to contain some radical error. This seems the most correct definition, but the word is used loosely. Its general signification, namely, a specious proposition, is perhaps nearest the mark. Truly considered, most errors are sophisms, for errors are not direct contra dictions to the truth, but simply the leaving out of view one or more elements of the truth, and seizing on only one or two elements, and declaring them to constitute the whole truth. Victor Cousin defines
error to be " One element of thought considered exclusively, and taken for the complete thought itself. Error is nothing but an incomplete truth converted into an absolute truth." (` Introduction h l'Hist. de Philosophic,' Lecon 7.) Spinoza had before defined "falsity to be that privation of truth which arises from ideas." (` Ethics,' b. ii. prop. xxxv.) It is sometimes a mere confusion of terms ; as in the common example of—Bread being better than paradise;• because bread is better than nothing, and is better than confusion arises from both the " nothings " being used substantively ;, whereas it is only the first that is so used ; the second is affirmative, and expresses " there is nothing better." A sophism is therefore the use of some word in a different sense in the premises from that in the conclusion, and this is the definition of Aristotle (` Top.' viii. 11) : " When the discourse is a demonstration of anything, if it contain anything which has no relation to the conclusion, there will be no syllogism ; and if there appear to be one, it will be a sophism, and not a demonstration." This confusion of words and ideas is the origin of all errors and sophisms ; but though errors and sophisms are logically constituted alike, yet the instinctive sense of mankind marks the difference between incomplete views (error) and wilful perversion (sophism). In all cases a sophism is supposed to be recognised as such by the sophist. It is an endeavour on his part to "make the worse appear the better reason." It is the consciousness then of the sophist which distinguishes and renders odious his error as a sophism.