8() Mr. M. M. Pattison Muir on Chemical Classification. 



gether from the sway of imagined " principles." Although 

 he knew of oxygen only in the form of gas, he nevertheless 

 could scarcely accept the results of e:jj:periment, but endea^ 

 voured to regard gaseous oxygen as pure or ^^ concrete " 

 oxygen, phis a something which he called caloric^ He ap-« 

 pears to have thought that all "pure" substances were 

 solids, and that by combining with this subtle kind of 

 matter, caloric, they became first liquids and then gases. 

 In Lavoisier's time the conception of matter and force as 

 distinct, but real, existences had not become generally ac,-! 

 cepted among scientific men, although the Frlncipia had 

 been written sixty years before. The doctrine of Phlogiston, 

 although extinguished in its more palpable form by Lavoi- 

 sier himself, keeps, nevertheless, reappearing in this theory of 

 the action of caloric. If we interpret both theories, the Phlo- 

 gistic and the Caloric, in the light of modern doctrines of 

 energy, we find much truth in each. Again, Lavoisier's 

 generalization regarding the nature of acids Avas not based 

 upon a sufficiently large number of facts. This generali- 

 zation led him astray ; it led him to forsake the plan of 

 strictly experimental inquiry which he had laid down for him- 

 self. On the hypothesis that all acids contain oxygen, it fol- 

 lowed that nmriatic acid must contain this body ; but no one 

 had been able to separate oxygen from muriatic acid ; hence, 

 on Lavoisier's own showing, he should not, on the strength of 

 a few experiments and a sweeping generalization, have re- 

 garded this acid as a compound of oxygen with an unknown 

 radicle. Again, although he found that certain elementary 

 substances were oxidized by heating with oxide of man- 

 ganese or with oxide of mercury, he was nevertheless not 

 justified, judged in the light of his own method, in assuming 

 that the action of the former of these compounds upon muriatic 

 acid was an oxidizing action, and in therefore concluding that 

 the gaseous product of this action was a more highly oxygen- 

 ated body than muriatic acid itself. An appeal to facts and 

 an interpretation of the observed facts in accordance with the 

 true scientific method which he had laid down, would have pre- 

 vented Lavoisier from perplexing the chemical world with hi^ 

 " unknown radicle of muriatic acid " and with his '' oxygenated 

 muriatic acid." But when Ave seethe errors which are beino^ 

 constantly made in our interpretation of facts, even when we 

 receive that aid which the advance of science affords to modern 

 naturalists, we cannot be otherwise than astonished at the 

 small number of mistakes made by Lavoisier, nor can we 

 grudge him the highest praise for the wonderful use Avhich he 

 made of his great powers of scientific ijuagination. 



