198 Proceedings Columbia Biochemical Association [March, 



of barium chlorid sol, and to C 3 drops of potassium sulfate sol., are 

 added. If not enough barium chlorid sol. has been added, B will 

 be cloudy; if barium chlorid is in excess, then cloudiness appears in 

 C. In either case the contents of the test tubes are carefuUy poured 

 back into the main sol, the test tubes and filter being thoroughly 

 rinsed with dist. water, and i cc. of barium chlorid or potassium 

 sulfate sol., depending upon which is in excess, is now added. The 

 tests are repeated. If, in the first trial, test-tube B gave a cloudiness 

 and, after the addition of another cc. of barium chlorid sol., it still 

 continues to give a cloudiness (whereas C is clear or far less cloudy 

 than B), there is evidently an excess of SO4 ions, and therefore more 

 barium chlorid is added. If the further addition of barium chlorid 

 causes the reverse to take place, namely, clearness or slight cloudiness 

 in B and decided cloudiness in C, there is an excess of Cl ions, and 

 therefore more potassium sulfate is added. It is evident that if, 

 with a given vol., the results are the reverse of those seen with i cc. 

 less, the end point must lie somewhere between these two volumes. 

 If the determination need be approximate only, then the average of 

 the volumes is taken. If not, further trials, with successive o.i 

 cc, are made, until a point is reached where 3 drops each of barium 

 chlorid and potassium sulfate sol. added to B and C give precisely 

 the same cloudiness. To confirm this endpoint, take a f resh sample 

 of urine, and add to it at once the total volume of barium chlorid 

 sol. Samples of the filtrate should give equal cloudiness with ba- 

 rium chlorid and potassium sulfate. 



IL Inorganic sulfates. The procedure is analogous to the above, 

 except that acetic is substituted for hydrochloric acid, and the Solu- 

 tion is not heated. 



I — II = Ethereal sulfates, 



III. Neutral sulfur. Here 50 cc. of urine are treated with 5 gm. 

 of potassium nitrate and 7 gin. of sodium carbonate. The mixture 

 is evaporated and then heated tili the carbonaceous mass is com- 

 pletely oxidized. The residue is dissolved in water, the sol. poured 

 into an Erlenmeyer flask, neutralized with hydrochloric acid and 5 

 cc. of hydrochloric acid sol. (sp. gr., 1.2) added. From here follow 

 I. This will give total sulfur. If the total-sulfate sulfur (obtained 

 in I) is subtracted from this, the result will be neutral sulfur. 



141. The respiratory exchange of fish. Sergius Morgulis. 



