l62 PHILOSOPHICAL TRANSACTIONS. [aNNO I674. 



ferent medicinal properties. I am not very forward to question and quarrel 

 with opinions and maxims established by universal consent, and confirmed by 

 the experience of many ages, unless I have sufficient reason to distrust their 

 veracity and validity. In the present case, the persuasion of the ancients, and 

 the position, which I shall endeavour to illustrate, though at the first appear- 

 ance they seem diametrically opposite, may be easily reconciled. I formerly 

 declared, that most vegetables burned whilst green or moist, and with a 

 sm.othering fire, yield a kind of neutral salt,- which may be called tartareous, 

 and sometimes not improperly essential, many of them retaining the vomitive, 

 purging, sweating, diuretical, opiate, or other general, and perhaps some spe- 

 cifical, properties, wherewith the plants were ennobled which produced them. 

 Now, whether it is some small quantity of the essential oil, which mixed with 

 the saline principle renders it so variously medicinal, the essential oils of plants 

 being manifestly as it were a compendium of the plant, which they do equally 

 exactly resemble in smell, taste, and other qualities : or, whether those virtues 

 are the result of the crisis and mixture of the several principles ; certain I am, 

 that, after the oil is evaporated by an intense heat, or the crasis disturbed by 

 avolation of some parts, and new combinations of what remains, farewell all 

 specifical qualities, and consequently all other differences, than what purity 

 and impurity, and several degrees of heat may occasion; some being more 

 white and fiery than others. Now some salts are much more easily deprived of 

 their acid and oily parts, than others and in some, on the contrary, the oil is 

 of so fixed a nature, or rather so closely combined with the other principles, 

 that it must be a very intense heat which can disjoin them, and thereby reduce 

 the salt to the common standard or aggregate of qualities, wherein all alcalies 

 agree. 



The industrious Tachenius somewhere pretends to demonstrate, that there is 

 a real difference between the alcalies of different plants ; which he would prove 

 by the various effects they have upon a sublimate dissolved in common water. 

 But this is easily resolved by what I before suggested; as also by an easy obvious 

 experiment, which may at any season in any plant be readily proved. Take 

 what wood or plant you please, burn it green ; the salt, being extracted out of 

 the ashes, will, according to the different degrees of fire to which it shall suc- 

 cessively be exposed, variously, influence the mercurial solution ; the several 

 preecipitates differing no less from each other, than when made with the salts of 

 different plants. 



This is also most evident in tartar, which, the less and more gently it is 

 calcined, the more salt it yields; and on the contrary, a much smaller propor- 

 tion, if suddenly and with the highest degrees of heat. That which is prepared 



