554 Scientific Proceedings, Royal Dublin Society. 



tube h of the apparatus. The flask is exhausted and the necessary 

 re-agent added through the cup and stopcock G. 



I trust in a future communication to the Society to give the 

 results of a research on certain methods of water analysis upon 

 which I have been engaged for some time past, and to show how 

 the apparatus may be conveniently employed for determining the 

 dissolved gases, organic carbon, and the nitrogen in waters. 



In the early part of this paper it was pointed out that the 

 reservoir supplying mercury to the burette and pressure tube was 

 connected with the latter and not with the former. With this 

 class of apparatus such an arrangement is essential, because, when 

 the reservoir is kept for any length of time at a lower level than 

 that of the bottom of the burette, and this is constantly necessary 

 when working in vacuo or under reduced pressure, air diffuses 

 through the indiarubber connecting tube, and passes into the 

 pressure tube immediately the reservoir is raised again. It would of 

 course pass into the burette, and the experiment would be vitiated if 

 the connecting tube were directly attached to the burette. The air 

 may be expelled from the pressure tube when necessary by opening 

 its stopcock and raising the reservoir sufficiently high to fill the 

 tube with mercury. 



It will be noticed that the pressure tube is not provided as in the 

 case of Thomas' or Macleod's apparatus with a water jacket for keep- 

 ing its contents, when employed as a closed and " wet" pressure tube? 

 at the same temperature as the contents of the burette, nor are 

 means furnished for continually renewing the water in the cylinder 

 C during an analysis. I have found that neither additions are 

 necessary to this class of apparatus for all ordinary purposes. 

 Since the burette is of a considerable length, viz. 640 mms., the 

 measurements may in nearly all cases be made with advantage 

 with an open pressure tube ; and if the cylinder C be filled with 

 water that has been kept exposed for some time to the temperature 

 of the laboratory in which the apparatus is kept, the water will not, 

 if ordinary care be observed, alter sufficiently to appreciably affect 

 the results of an analysis. When it is necessary to use a closed 

 pressure tube and it is at the same time necessary to work with 

 the utmost degree of accuracy, then it is preferable to employ a 

 " dry " closed tube; but even if it be employed " wet " very good 

 results will be obtained. The additions above referred to have the 



