24 ESSAYS BIOGRAPHICAL AND CHEMICAL 



if possible, experimentally tested; if true, kept; if false, 

 rejected. 



Thus, early in the book, we meet with the phrase, long 

 accepted as true, ffomogenea congregare ; that is, 'Like 

 draws to like.' This Boyle disproved by showing that 

 liquids, like alcohol and water, alike in being colourless 

 and transparent, although they mix with each other, may 

 be easily separated by freezing; for, when cooled, the 

 water freezes, leaving the alcohol unfrozen. Here we find 

 the first record of experiments on a subject which, in 

 Raoult's hands, yielded such extraordinarily important 

 results. Another of Boyle's arguments is, that although 

 liquids and gases mix respectively with each other, yet 

 solids show no such tendency, and do not even cohere, 

 except in cases where the cohesion can be explained 

 by the form of the solid, and the consequent exertion of 

 atmospheric pressure. 



After making a number of such attacks, Boyle proceeds 

 to consider the hypothesis at that time all-prevalent and 

 universally accepted, of the elements salt, sulphur, and 

 mercury. He opens two distinct lines of attack. His 

 first may be stated thus : If all substances are composed 

 of salt, sulphur, and mercury, and if vegetable and animal 

 substances contain, as is stated, much mercury, little 

 sulphur, and less salt, then it is desirable to show that a 

 vegetable may be constructed of a substance containing 

 none of these principles, but only of water, which was 

 then sometimes termed ' phlegm/ and was ranked among 

 the elements. This he attempted by growing a ' pompion ' 

 in a weighed quantity of earth, and after the pumpkin 

 had grown, he showed it to consist of water, by distilling 

 it ; and by weighing the earth, he proved that it had not 

 lost weight. He then turns to the c vulgar spagyrist/ and 

 triumphantly challenges the truth of his theory. It is 

 now known that the elements carbon and nitrogen, and 



