On the Decomposition of Water ly Charcoal. 303 



science varies in gaining new means of improving itself. 

 Since the publication of his work, M. Haiiy has already 

 made considerable changes in his system, but all of them 

 were foreseen and previously indicated, with the single ex- 

 ception of sphene, which he then knew only by some in- 

 distinct crystals. When one has laid down certain princi- 

 ples, the path of science is then found circumscribed, but 

 its march is direct : it it change, it is only for a rational 

 melioration, and it proceeds in advancing. If delivered to 

 the current of opinions, or of hypotheses, it is discussed in 

 every sense, and fortunate if it does not retrograde. For it 

 there is no more surety, each one buffeting it at his pleasure. 

 To reform is a great art, and to retouch without defacing 

 requires great ability. Principles produce improvements, 

 arbitrariness induces revolutions. 



M. Haiiy had formerly determined the molecule of spar- 

 gelstein [asparagus -stone, the chaux phosphatce chrysolithe 

 of Haiiy and Brogniart] as well as that of appatite; but at 

 an interval of several years, as the idea of comparing his 

 results did not occur till M. Vauquelin had discovered that 

 spargelsiein is a phosphate of lime. Here chemistry was 

 found to agree with crystallography. 



A mineral was discovered, which some thought to be of 

 the calcareous genus, which dissolved in acids without 

 either effervescing or emitting fluoric acid., but which never- 

 theless gave traces of a combination with an acid ; and M. 

 Werner pronounced it a phosphate of lime. He was not 

 deceived ; but the difference which there is between reason- 

 ing and divining, is, to set out on a principle, or to start at 

 hazard. Yet, even in setting out on a principle, we are 

 not always sure of reasoning. Phosphorus in burning is 

 phosphorescent and odorous ; quartz when rubbed has the 

 same properties; therefore silica is composed of phosphoric 

 acid and lime. It is thus that a very celebrated German 

 professor spoke, and he pretended to reason : his preten- 

 sions were so much the greater, that the combination of 

 phoshoric acid and lime is neither phosphorescent nor 

 odorous. 



[To be continued.] 



LVIT. On the Decomposition of Water hy Charcoal. By 

 M. Tordeux, Student of Chemistry in the Polytechnic 

 School*. 



Xn the note at the end of the observations of M. Flguier, 

 «n the sulphurets contained in the soda of commerce, in a 



• Annaits dc Chimiot tome lxvi. p. 318. preceding 



