24 MINERAL WATERS OF THE UNITED STATES. 



(containing the iodin in solution) transferred to a 12 cc Nessler a tube 

 by means of about 5 cc of pure carbon bisulphid. The contents of 

 the tube is made up to the mark and the color matched with that of 

 other 12 cc tubes containing known amounts of iodin dissolved in 

 carbon bisulphid. These standard tubes are prepared by taking meas- 

 ured quantities of a solution of known potassium iodid content, acidi- 

 fying with sulphuric acid (1 to 5), adding 3 or 4 drops of potassium 

 nitrite, and extracting with carbon bisulphid just as in the actual 

 determination. 



The filtrate from the carbon bisulphid is now used for determining 

 biomin. To the filtrates from the iodin standards, different measured 

 quantities of a potassium bromid solution of known strength are now 

 added, the standards being run along with the actual determination 

 and conducted in exactly the same way. The filtrates (both from the 

 actual determination and from the standards) are transferred to small 

 flasks and freshly prepared chlorin water added. Usually 2 to 8 cc of 

 & saturated solution of chlorin is sufficient. Care must be taken not 

 to add too much chlorin in excess of that necessary to set the bromin 

 free, since a bromo-chlorid is apt to be formed with an excess of the 

 reagent, thus spoiling the color reaction. 



It was found also that the best results are obtained by adding 

 approximately the same excess of chlorin to the standards as to the 

 actual determination. This may be accomplished by adding the chlorin 

 water 1 cc at a time and shaking between additions. After a little 

 practice one can approximately determine when the chlorin ceases to set 

 bromin free. After all bromin has been thus set free, 5 cc of freshly 

 purified carbon bisulphid is added to each of the flasks and the whole 

 well shaken. The water solution is now filtered off from the carbon 

 bisulphid through a moistened filter, the contents of the filter washed 

 two or three times with water and then transferred to a 12 cc Nessler 

 tube by means of about 1 cc of carbon bisulphid. This extraction of 

 the filtrate is repeated twice, using 3 cc of carbon bisulphid each time. 

 The combined carbon bisulphid extracts usually amount to about 11.5 

 cc to 12 cc. If they do not come quite up to the 12 cc mark, enough 

 carbon bisulphid is added to each tube to bring them to the required 

 volume and the sample is then compared with the standards. In some 

 cases when working with th,e method near its upper limit the authors 

 found that the bromin was not quite all extracted by the amounts of 

 carbon bisulphid recommended above. In such a case one or two extra 

 extractions with carbon bisulphid were made, the extracts were trans- 

 ferred to another 12 cc tube, and the color compared with some of the 

 low standards. 



This tube was made from the ordinary 10 cc Nessler tube by re-marking it at the 

 level of 12 cc of liquid. 



