58 SCIENCE PROGRESS 



water, the greater part of a carboy, and the difficulties in the 

 way of isolating it are such as any chemist -can understand. 



As a matter of fact, the accurate determination of the sodium 

 is a form of amusement in which the ordinary water analysts do 

 not indulge. Sometimes the alkalis sodium and potassium are 

 determined together by difference, that is, not determined at all. 

 In a paper 1 that has been sent to me recently the analyst 

 describes his methods. In this case, everything possible is got 

 rid of by the usual methods of precipitation, and the remainder 

 is evaporated and weighed as "Sodium and Potassium Chlorides." 

 The amount dealt with is only that from 250 cc. of filtered 

 water, and would, of course, be infinitesimal, and the fact that it 

 amounts to not more than 2 or 3 per cent, of the total dissolved 

 solid is a good indication of the general accuracy of the analysis. 

 The residue includes, of course, everything that is not caught by 

 the filter throughout the whole operation. It should be men- 

 tioned, also, that the samples usually stand for days in glass 

 bottles. In such cases of water analysis when the sodium and 

 the potassium are separated, the separation is, needless to say, 

 a very approximate operation. 2 



It is no reflection on the accuracy of river water analysts to 

 say that the results are of no value whatever for Prof. Joly's 

 purpose. No one, except Prof. Joly and a few geologists, wants 

 to know the proportion of sodium in river water. It is at the 

 same time the constituent least important for the purposes of 

 the water analyst and the constituent most difficult to determine. 

 The assumption on which Prof. Joly proceeds, that 347 per cent, 

 of the dissolved matter in river water is sodium, is absolutely 

 unproven. For all the analyses prove, it might be less than half 

 that amount. Indeed the principal evidence that there is an 

 excess of sodium over and above its equivalent of chlorine is 

 indirect rather than direct. The results of rock analyses are 

 more reliable and it seems to be established that the sodium 

 content of igneous rocks is greater than that of the aqueous. 

 As a matter of fact it has been pointed out by Prof. Dubois that, 



1 "The Quality of the Surface Waters of Illinois," U.S.A. Geological Survey, 

 Water Supply Paper No. 239, p. 16. The method is the one usually recom- 

 mended in the text-books. See Wanklyn, nth edition, p. 122. 



- The potassium determination would be the more accurate of the two, as the 

 potassium is weighed as Pt. + 2KCI. A further percentage of inaccuracy would 

 thus be thrown on the sodium. 



