August 30, 1912] 



SCIENCE 



263 



1. The formation of the resins from the 

 simple aldehydes. 



2. The formation of the resins from the 

 complex aldehydes or carbohydrates. 



3. The formation of the resins from the 

 terpenes. 



It is not impossible that the resins are 

 formed by any one of the above syntheses. 

 There are abundant reasons for believing, 

 however, that the synthesis of many of the 

 resins is intimately related to the terpenes, 

 that is, the terpenes may be first formed 

 from simple compounds as the hemiter- 

 penes, then converted into the resins by 

 condensation and oxidation. This reaction 

 seems entirely in accord with the chemical 

 changes which naturally take place as phy- 

 tochemical changes usually proceed from 

 the simple to the more complex, as for ex- 

 ample, from formaldehyde to the carbo- 

 hydrates, but never from the carbohydrates 

 to formaldehyde. 



From the study of these terpene deriva- 

 tives, it seems more than probable that the 

 resins, at least those on the pine family, 

 bear the same general relationship to the 

 terpenes that naphthalene does to benzene 

 and that the terpene molecule, CioHig, is 

 the common substance from which the res- 

 ins are derived. 



G. B. Frankfobter 



University of Minnesota 



TEE METAPHOR IN SCIENCE 

 There are several examples in the history 

 of science where an idea at first represented 

 by some metaphorical expression became in 

 course of time a concrete existence. Most of 

 the sciences have instances of it; one meets 

 first with a notion, often of the vaguest, a 

 principle, a property, a potentiality for some- 

 thing or other, and one ends with a substance, 

 a species of matter, tangible and ponderable : 

 the notion has become incarnated. 



Inorganic chemistry offers us an excellent 

 case of this sort of thing. When Lavoisier 



was working out the character of the sub- 

 stance we now know as oxygen, he had not 

 isolated oxygen by a stroke of genius and then 

 proceeded to study the properties of the new 

 chemical product; the history of its discovery 

 was far otherwise. Acting on some hints 

 given him in October, 1774, by Joseph Priest- 

 ley, Lavoisier came upon what he soon named 

 as the " principle of acids " or " the acidifying 

 principle"; his words are (1777) : 



I shall therefore designate dephlogisticated air, 

 air eminently respirable, when in a state of com- 

 bination or fixedness by the name of acidify-ing 

 principle or if one prefers the same meaning in a 

 Greek dress by that of oxygine principle. 



Here it is a principle, something which com- 

 bines with metals when they are calcined or 

 burned in air; it is that something which to 

 Lavoisier seemed essential in acids, that which 

 produced acidity, the oxygine principle. In 

 its later and more familiar form of oxygen, 

 it is better etymologically. That which was 

 a principle in 1777 was about 120 years after- 

 wards a visible, tangible entity — the liquefied, 

 steel-blue oxygen gas. The principle of 1777 

 by 1897 had become a substance; the meta- 

 phor had become an actuality. 



Not all chemical concepts have been equally 

 fortunate in leading to true and individual 

 chemical substances : phlogiston, for instance, 

 denoting, as it did, no reality, is the concep- 

 tion phlogiston still. The principle of heat, 

 phlogiston, was supposed to leave a body when 

 it was burned: the theory of Stahl asserted 

 that heat was a thing, a thing which could 

 depart from a body and leave it lighter than 

 before when it was cold. Now this, as a con- 

 ception, is sufiiciently definite, but as it is not 

 true in fact, phlogiston never materialized; it 

 was never isolated from matter because it 

 never existed in matter. Phlogiston was as 

 barren a conception as " oxygine " was preg- 

 nant. To-day Priestley and Lavoisier could 

 be presented with an ounce or so of the 

 '■■ oxygine " principle, but not a milligram of 

 phlogiston could be extracted for Stahl, for 

 oxygen is a substance, but heat is a mode of 

 motion. Probably the most pregnant meta- 

 phor ever used in science was Harvey's as 



