Dr. Kane on the Coinporinds of the Oil of Peppermint. 419 



indeed pretty broadly, although without having analysed the 

 liquid oil, which he might so readily have done, that the for- 

 mula of Blanchet is the true one, and that mine, in as far as 

 it differs from it, is likely to be incorrect. His words are : 

 " Si I'essence de menthe poivree liquide presente la meme 

 composition que I'essence de menthe concrete, ce qui est tres 

 probable d'apres les observations de M. Robert Kane, qui 

 est conduit cependant, quoique le rapport numerique qu'il a 

 trouve, soit le merae, a adopter une formule different de celle 

 que je viens de presenter, formule du reste qui n'est deduite 

 ni de la densite de la vapeur, ni d'aucune combinaison dans 

 lequelle I'essence de menthe rentrerait," &c. Now I purpose 

 to show in this notice that Mr. Walter has not done justice 

 to his own analyses; for that by giving them their just inter- 

 pretation, he would have found Blanchet's formula to be in- 

 exact, and that the stearopten possesses the precise constitu- 

 tion which I have assigned for the oil. 



In an organic analysis the sources of error act in opposite 

 directions on the carbon and on the hydrogen ; there cannot 

 be more carbon obtained than was present in the substance ; 

 and from the facility with which the hydrogen is burned, 

 there is never less water obtained. In practice, a chemist 

 very seldom succeeds in a complete combustion of the carbon ; 

 and almost in all cases, from the hygrometric nature of his 

 materials, he gets more water than he ought. Hence in de- 

 ducing a formula from a set of analyses, the highest number 

 obtained for the carbon, and the lowest number obtained for 

 the hydrogen, are those most likely to be true, and are those 

 on which the formula should be constructed. There may be 

 cases in which water may be lost, but it must arise either from 

 an error in weighing or from bad management in the analysis. 

 Setting out from these principles I will proceed to discuss 

 Mr. Walter's numerical results. 



In six analyses of the solid oil, the highest value he ob- 

 tained for the carbon was 77"68, and the mean of five results 

 was 77'36. The lowest result for hydrogen was 12'52 and 

 the mean of four was 12-66. Mr. Walter's analyses and 

 theory are therefore, — 



Analysis. Analysis. 



Carbon 77*68 77*36 



Hydrogen.. 12*52 12-66 



Oxygen . ... 9-80 9*98 





Theory. 



^90 



77*27 



Wqo 



12-62 



O 



10*11 



100-00 100*00 100-00 



It is also quite evident that the results of Mr. Walter's 

 analyses cannot be considered as exceedingly correct, when 



