Traite Elementaire des Reactifs. 329 



substances entitled to this distinction, insisting particularly on tiic 

 criteria of their purity ; for the chief part of the mis-statements and 

 contradictions to be found in chemical worl<s, has been occasioned 

 by the employment of impure re-agents. The details of their pre- 

 paration should be referred to the ordinary systems of chemistry. 

 After pointing out the means of verifying the justness of the tests, 

 we should next detail their applications, stating fully the pre- 

 cautions to be observed in their use, and the peculiar phenomena 

 which they produce with their correlative objects. 



The second part of the treatise should present in a systematic, 

 and, if possible, in a tabulated form, the various objects of chemi- 

 cal research, simple and compound, with their corresponding tests. 



In the third, and concluding division, formulae illustrated by 

 examples, somewhat in detail, should be given, for evoking in suc- 

 cession the several constituents of a compound by the successive 

 applicalion of their appropriate re-agents. 



Mess. Payen and Chevallier have incurred for their treatise the 

 blame of confusion and tautology, by adopting a defective arrange- 

 ment. In their second chapter we have an account of the action 

 of heat on a long list of substances, placed in alphabetical order; 

 which account would have been better introduced under the de- 

 scription of the various bodies in subsequent chapters. No use, 

 however, is made of the indications of Berzelius. The rambling 

 manner in which our authors sometimes indulge themselves, in 

 trite details, may be judged of from the following specimen : 



Tin melts at 228° centig. At a much higher temperature it is reduced 

 into vapour : vi-hen elevated to a red heat, if we throw it on the hearth it is 

 dividecl into incandescent globules, which bum less vividly than those of 

 antimony. It is distinguished, further, from this metal, because it leaves a 

 greyish oxide, heavier than its oxide. Tin is susceptible by the action of 

 heat of being totally oxidized, if we take care to remove the oxide in pro- 

 portion as it forms on the surface of the metallic bath. By this oxidation 

 the metal augments in weight. Brun, apothecary at Bergerac, is the first 

 who took notice of this phenomenon ; not knowing the cause of it, he con- 

 sulted Jean Rey, physician, who replied, that " the air had become fixed 

 in the metal." Tbis bold reply should have put people in the way of seeing 

 the composition of the atmospheric air. It was long alterwards, however, 

 before its composition was discovered. P. 20. 



What they are pleased to say of the blow-pipe is extremely 

 va^ue, shewing that they were unacquainted with Berzelius's in- 

 structions for the use of this admirable test, a subject which they 

 dismiss with a foot-note reference to his Traite sur le Chalumeau. 

 They speak indeed of the different intensities of heat in the different 

 parts of the flame, but never hint at the opposite powers of oxida- 

 tion and reduction which it possesses ; the most important discovery 

 ever made in the science of the blow-pipe. — See our Extracts on 

 this subject in vol. xiii. p. 32.5, of this Journal; as also Children's 

 Berzelius, pp. 29 and 49. 



The third chapter is of great length. It treats of simple com- 

 bustibles and their oxides. We shall take a cursory '. iew of some 

 of its particulars. We find chlorine recommended for demon- 

 strating the prescnci' and proportion of sulphuretted hydrogen, by 



