Chemical Instruments and Operations. 265 



METHOD OF ASCERTAINING THE PURITY OF NITRIC OXIDE. 



Eudiometrical process by Nitric Oxide and Green Sulphate, 

 or Muriate of Iron. 



The purity of nitric oxide is easily ascertained, by means 

 of a solution of green muriate, or green sulphate of iron, and 

 the sliding rod eudiometer above described. A small bottle 

 being filled with a solution of the salt, and inverted upon the 

 shelf of the hydro-pneumatic cistern, take into the eudiome- 

 ter one hundred measures of the gas and transfer them to 

 the bottle, which must be agitated for two or three minutes. 

 The receiver (fig. 2) being filled with water, and depressed 

 into the water of the hydro-pneumatic cistern, till the apex, 

 A, is on a level with the surface ; throw up into it the resid- 

 ual gas. In the next place, draw it into the eudiometer. 

 The distance which the rod is drawn out, shows the quanti- 

 ty, which may be again ascertained in ejecting it from the 

 tube. A saturated solution of nitric oxide, in the above-men- 

 tioned ferruginous solutions, has the power of absorbing oxy- 

 gen, and was consequently recommended by Sir H. Davy, as 

 the means of ascertaining the quantity of that gas in the air. 

 The mode of using them would be the same as that just de- 

 scribed, taking atmospheric air into the eudiometer, instead 

 of nitric oxide, and filling the bottle with the ferruginous so- 

 lution of nitric oxide, instead of the pure sulphate, or muriate 

 of iron. 



I have found this method of ascertaining the quantity of 

 oxygen, in the air, much more tedious, and much less satis- 

 factory, than those already described. 



1. DESCRIPTION OF AN IMPROVED MERCURIAL SLIDING ROD 

 EUDIOMETER. 



The aqueous sliding rod hydro-oxygen eudiometer,* al- 

 though perfectly well qualified for experiments, in which wa- 

 ter is employed, does not answer well when used over mer- 

 cury. The great weight of this hquid causes the indications 

 to vary, during manipulation, in consequence of changes of 

 position too slight to be avoided. 



The instrument represented in the figure on the opposite 

 page is furnished with a water gage, O M, which, being ap- 

 pealed to, enables us to cause the pressure of any contained 



* See this Journal, vol. x, page 67. 

 Vol. XV.— No. 2. 9 



