1822.] the Organ of Hearing in Fhhes, 325 



separated from it, and indeed have no communication with it 

 except by two very small ducts. One of these ducts passes 

 from the vestibulum membranaceum to the posterior canal, 

 which has the form of a circle, and does not cohere to the 

 remaining canals ; the other passes to the anterior canal. 



25. The observation of Treviranus that the auditory nerves are 

 not always to be considered as branches of the trigeminus is 

 proved to be true. 



26. The nervi auditorii accessorii have different origins in 

 different fishes ; proceeding from the cerebrum, the par vagum^ 

 a:nd the trigeminus. Nor are these nerves always destined ta 

 the same parts of the labyrinth. In the raia torpedo, the squalus 

 carcharias and the petromyzon {lamprey)^ the nervi auditorii 

 accessarii do not belong to the ear. In several of the cyprini, 

 the author describes a very remarkable deviation in these 

 nerves. 



27. The branches of the nervi auditorii belonging to the ves- 

 tibulum are soft^ and, as it were, spread over its inferior surface. 

 The branches sent to the ampullae are hardy and penetrate into 

 the cavity of the ampullae, constituting a semilunar plexus jut- 

 ting out into the cavity. The sonorous tremors of the fluid 

 included in the semicircular canals are readily transferred to 

 these nerves. The nerves of the vestibulum receive the sono- 

 rous tremors of the solid bodies included in the vestibulum or 

 sack. 



Article II. 



On the Annlysis of Brass. By Mr. W. M. Keates. 



(To the Editor of the An?iak of Philosophy.) 

 SIR, 



Having noticed that most chemical writers, who have made 

 mention of brass, state the proportions of the two metals which 

 compose that alloy, to be very different from what they really are, 

 I was induced to attribute the incorrectness of their statements 

 to some fallacy in the mode of analyzing it ; this opinion was 

 verified by some experiments which I made on the subject. 



The formula recommended by the most eminent writers is 

 solution of the alloy in dilute nitric acid, adding excess of 

 caustic potash, boiling, to take up the oxide of zinc, and throw 

 down the oxide of copper. 



This method of proceeding seems to have been followed from 

 a consideration of the known habitudes of each oxide whea 

 per se, rather than founded on the result of direct experi- 

 ment. For although the oxide of zinc, when alone, is readily 

 soluble in an excess of caustic alkali, yet when precipitated along 

 with oxide of copper, a part only is taken up by that menstruum^ 



