Chemical Instruments and Operations, 215 



\vhich is absorbable by water, it is not necessary to employ 

 mercury, and, consequently, to have the metallic part of the 

 eudiometer of iron and steel. It is in fact preferable to have 

 it of brass, as in that case it will not rust, and may be kept 

 in operation for many months, without requiring much ad- 

 justment. I have an apparatus thus made, and so contrived 

 as to be ignited by an electric spark. Excepting the substi- 

 tution of brass for iron, there is no material difference be- 

 tween that apparatus and the one represented by the figure, 

 excepting that the receiver, E, is exchanged for one of which 

 there is an engraving in the Compendium.* 



In the brass eudiometer last described, the cock, C, is' 

 omitted; while, at right angles to the receiver, a small cock 

 is inserted, which supports a glass vessel holding water. By 

 these means, any excess or deficiency of this liquid is easily 

 remedied, and the employment of the cup, beneath the eudi- 

 ometer, rendered unnecessary. 



8. DESCRIPTION OF THE VOLUMESCOPE. 



In the next page there is an engraving of an instrument 

 which I have advantageously employed, in order to illustrate 

 the experimental basis of the theory of volumes, and some 

 other eudiometric phenomena. 



As I find it very inconvenient not to have a name for eve- 

 ry variety of apparatus, I shall call this instrument a Vol- 

 umescope. 



It consists of a very stout glass tube, of thirty-six inches in 

 height, and tapering in diameter inside from two and one- 

 eighth to one and one-eighth inches. The least thickness of 

 the glass is at the lower end, and is there about five-eighths 

 of an inch. There is an obvious increase in thickness, to- 

 wards the top, within the space of about six inches. The 

 tube is situated between the iron rods, I I, which are rivet- 

 ted, at their lower ends, to a circular plate of the same metal 

 let into the lower surface of a square piece of plank. This 

 piece of plank supports the tube, so as to be concentric with 

 an aperture corresponding with the bore of the tube, and 

 constituting effectively its lower orifice. The upper orifice 

 of the tube is closed by a stout block of mahogany, which 

 receives a disk of greased leather in a corresponding hollow, 

 formed, by means of a lathe, so as to be of the same diame- 

 ter as the end of a tube. Into a oerforation in the centre of 



* See Article 124 of that work, fig. B. 



