1869.] The Fidure Water-suj^phj of London. 241 



went, perfect ; but, imfortunately, this is not the case. Pure urea 

 does not yield the whole of its nitrogen under the circumstances 

 of the experiment, and neither does pure albumen, unless with 

 extreme difficulty. The authors believe that the ammonia obtained 

 bears a definite and constant relation to the amount of those com- 

 pounds present, and think themselves justified in calculating the 

 amounts of urea and albuminoid compounds from the figures they 

 obtain; but such a method is obviously inferior to one which 

 should give more positive results. The process is very easy of 

 application, and, as an empirical method of judging of the goodness 

 or badness of a water it is certainly valuable. It gives concordant 

 results ; and though it is somewhat difficult to give a distinct inter- 

 pretation of those results, without venturing on hypothetical ground, 

 it may, I think, safely be used, when the more exact method of 

 Frankland and Armstrong cannot be applied, as a means of judging 

 whether a given sample of water is, or is not, fit for drinking purposes. 

 Water which yields very minute traces of the so-called ureal and 

 albuminoid ammonia, and is free from nitrates, can never, I believe, 

 be injurious. 



The process of Frankland and Armstrong, alluded to above, is 

 described in their previously quoted paper, and is unquestionably 

 the most important contribution to the study of potable Avater 

 which has ever appeared. In this wonderfully exact and ingenious 

 method, the dried residue of the water, which has been previously 

 deprived of carbonic, nitric, and nitrous acids, by boiling with sul- 

 phurous acid, is ignited with chromate of lead in a combustion-tube 

 sealed at one end, and connected at the other with a Sprengel-pump, 

 by which a perfect vacuum is effected at the commencement of the 

 experiment. During the ignition of the residue, the organic carbon 

 is converted into carbonic anhydride, and the nitrogen is evolved 

 either free or as nitric oxide. "When the combustion is complete, the 

 pump is again worked, and the gases formed during the experiment 

 swept down by the falling mercury, and collected in an ordinary 

 mercurial trough. They are then removed to another piece of 

 apparatus, and measured and analyzed by known methods. Such, 

 divested of details, is an outline of this remarkable process. It will 

 be seen that no attempt is made by it to ascertain the absolute 

 amount of organic matter present ; but it furnishes us with precise 

 information in regard to two of the most important elements of 

 that organic matter, namely, the carbon and nitrogen. From the 

 nitrogen found in the experiment must be deducted that present in 

 the original water in the form of ammonia. A separate experiment 

 must be made for this purpose, and a second for the determination 

 of the nitrogen present, as nitrates, and nitrites, which yield their 

 nitrogen in the form of nitric oxide when agitated with mercury 

 and sulphuric acid. As the nitrogen, present as nitrates, nitrites, 

 and ammonia, are used as a measure of previous scwage-contaraina- 



