fairchild: MiNERAiy sulphide: water 561 



gm. NaOH per liter. This amount was divided as follows: 

 NaOH equivalent to S", 0.195 gm. per liter; NaOH equivalent 

 to CO3", 0.382 gm.; NaOH equivalent to HCO3', 0.064 gm. — a 

 total of 0.641 gm. NaOH per liter, or a difference of 6.4 per cent 

 from the titration value. 



The apparatus for determining carbon dioxide was of the 

 usual form, a good illustration of which can be found in figure 

 21 (page 218) of Bulletin 700 of the United States Geological 

 Survey. The only change made was the substitution of a Peligot 

 tube containing K2Cr207 + H2SO4 for the calcium chloride tube 

 which is attached directly to the water condenser. This mixture 

 was preferred for oxidizing traces of hydrogen sulphide and ab- 

 sorbing moisture and fumes of ammonia as explained further on. 



The method. — Briefly, the method used is based on the expul- 

 sion of half bound carbon dioxide together with volatile hydro- 

 gen sulphide from the sample by boiling it for 5 minutes in a 

 rapid current of pure hydrogen, and fixing these products in an 

 absorbing solution composed of ammoniacal chlorides of cad- 

 mium and barium. This is the first operation. The second 

 involves the separation of these volatile products by acidifying 

 this ammoniacal mixture with acetic acid in order to liberate 

 again the carbon dioxide while the hydrogen sulphide remains 

 fixed as cadmium sulphide. The ammoniacal absorbing solu- 

 tion is composed of 10 cc. strong ammonia, freed from CO2 and 

 containing a few cc. of BaCl2 solution, about 5 cc. CdCl2 solution 

 (i cc. = o.oi gm. S), and about 20 cc. water free from CO2. 

 This solution is contained in a Peligot tube which is attached 

 directly to the water condenser. A 100 cc. sample of the arti- 

 ficial water was taken by means of a pipette and introduced into 

 the boiling flask. A stream of purified hydrogen (from Zn -f- 

 HCl) was passed rapidly for a few minutes through the appa- 

 ratus; then heat was applied to the flask, which was boiled 

 vigorously for 5 minutes and allowed to cool fior half an hour 

 in the current of hydrogen. The Peligot tube containing CdS 

 and possibly BaCOs was then substituted for the flask whose 

 remaining sulphide content was precipitated by the addition 



