Chemical Instruments and Operations. 26 S 



mark for nine hundred measures. The whole quantity of 

 the air and gas taken, being fifteen hundred measures, if on- 

 ly eight hundred and fifty are left, six hundred and fifty have 

 disappeared, which, divided by 3, gives 216.6. It follows, 

 that in 1000 measures of air, there are 216.66 measures of 

 oxygen, and of course in 100 measures, 21.6. 



The result corresponds more nearly with those obtained 

 by the hydro-oxygen eudiometer, when, by means of a flexi- 

 ble leaden pipe, forming a communication between a volu- 

 meter and the top of the tube, we are enabled to introduce 

 the nitric oxide over the air, instead of passing it up through 

 the water. 



The volumeter with which the pipe forms a communica- 

 tion, is, in shape, like the glass of the simple valve volume- 

 ter ; but instead of being similarly accoutred, has only a 

 brass cap and cock. To the latter, the pipe is attached. It 

 should hold exactly five hundred measures of the sliding rod 

 gas measure, in order to correspond with the marks upon 

 the tube, made as above described. 



Supposing that there is twenty-one per cent, of oxygen in 

 the air, there would be two hundred and ten parts of oxygen 

 in the one thousand measures taken, which would require 

 four hundred and twenty measures of nitric oxide. Hence, 

 it is probable that a volumeter holding a smaller quantity 

 than five hundred measures, would answer for a thousand 

 measures of air. The less nitric oxide there may be unne- 

 cessarily present, the less the risk of error, from its absorp- 

 tion. 



Sliding rod Eudiometer for Nitric Oxide. 



Fig. 2, represents the form of the sliding rod eudiometer, 

 which I have found most serviceable for experiments with 

 nitric oxide gas, or those in which sulphate, or muriate of 

 iron, saturated with nitric oxide, is employed. 



The rod for these experiments, is graduated into one hun- 

 dred and fifty large divisions, severally divided into five small 

 ones, which, being each considered equal to two degrees, 

 the whole number of degrees may be assumed either as one 

 hundred and fifty or fifteen hundred. 



The mode in which the rod is made to measure gaseous 

 fluids, has been explained. 



