Description of a Manometer. 46$ 



a n olive-coloured precipitate with the solution of highly 

 oxidated iron, instead of a blackish blue precipitate: a fawn- 

 red precipitate with the muriate of copper, instead of a blue 

 precipitate. 



Hence we see that, in the application to the arts, we may 

 obtain from the campeacby a different colour, according to 

 the kind of vessel in which we make the decoction : that 

 the action of the air, at least when it is continued too long, 

 changes its nature and decomposes it : so that the decoction 

 kept by the name of campeacby juice may be spoiled, if we 

 allow it to undergo the action of the air without some pre- 

 caution. 



Results were obtained different from the two foregoing, 

 when we submitted gall-nuts to the. test of the mano- 

 meter, with the view of examining what passed in the de- 

 velopment of the gallic acid : a portion of the oxygen of 

 the air is transformed into carbonic acid by means of the 

 carbon of the substance; but another portion also is libe- 

 rated, the two elements of which it had furnished ; and 

 lastly, there is a considerable absorption of azote; a cir- 

 cumstance which requires ulterior observations. 



Explanation of the Plate which represents the Manometer, 

 * and of the Method of using it. 



Fig. I and 2. Vertical and horizontal projections of a 

 cylindrical manometer formed by a vessel A with a large 

 aperture, the neck of which has a copper rim B. The in- 

 side of this rim forms a screw for receiving the plate of 

 copper E, which serves to close the manometer : it rests on a 

 round pad of leather so arranged that when the lid is screwed 

 down upon it, the vessel is very closely shut. G,G, but- 

 tons on which are fixed the notches of the key represented 

 flat in R, and seen directly in S ; this key serves to keep 

 the vessel steady, while we turn and fasten the lid with the 

 other key T ; the square head of which embraces the button 

 of the same form, which we see at E in the two projections. 



a, a j a, three hooks fixed in the lid from which we may 

 suspend a thermometer, a hygrometer, &c. D, a socket in 

 which we fix with hard mastic a barometer with a syphon : 

 as it would be difficult to give it, in this socket, a situation 

 exactly vertical, and besides, as the inclination of the screw 

 in the lid may remove it from this position, in order to oive 

 more precision to its indications, we rest the manometer on 

 a rim of wood, having three screws in it k, k, k, which we 

 move until the tube of the barometer be very vertical ; which 

 we may easily judge by means of the plummet IF, which 



Vol. 36. No. 152. Dec. 1810. 2 G is 



