118 



Norton — Action of Sodium Thiosulphate on 



the glass of the test-tube and porcelain lining of the Pfungst 

 tube precludes the possibility of an exact quantitative study of 

 the reactions involved. For the subsequent experiments, there- 

 fore, conducted upon the same general lines, a digester 

 with an interior cylindrical cavity of about 12 cm in depth 

 by 5 cm in diameter, and provided with a pressure gauge, 

 was employed. As a container for the solutions to be tested 

 use was made of a platinum cylinder, 4 cm in diameter and 10 cm 

 deep, provided with a loose cover. With this apparatus the 

 following quantitative experiments, which deal with those ele- 

 ments which are precipitated as hydroxides, namely, aluminum, 

 beryllium, chromium, zirconium and titanium, were made. 



In each case a weighed quantity of the salt taken for the 

 experiment was dissolved in 50 cm of water in the platinum ves- 

 sel, and to this a known amount of sodium thiosulphate was 

 added. The vessel was placed in the digester, and the latter 

 was heated by a Bunsen burner in the customary way until the 

 required pressure was shown on the gauge. The apparatus 

 was then cooled and the platinum vessel removed from the 

 digester. The precipitate was filtered off on ashless paper, 

 ignited, and weighed. 



Experiments with a Salt of Aluminum. 



In a series of experiments made according to the method of 

 Chancel, the results of which are shown in Table II, the solu- 

 tion in water of a weighed portion of pure ammonium alum 

 was treated with an excess of sodium thiosulphate and boiled 

 vigorously for periods varying from ten minutes to half an 

 hour. 



Table II. 





Amount of Alum 

 taken as A1 2 3 . 



Amount of N"a 2 S 2 3 . 



A1 2 3 found. 



Error. 





grms. 



grms. 



grms. 



grms. 



1. 



•0537 



Large excess 



•0471 



•0066 — 



2. 



•0537 



a a 



•0397 



•0140 — 



3. 



•1083 



« u 



•0931 



•0152- 



4. 



•1137 



5 grms. 



•0979 



•0158 — 



5. 



•1139 



2 " 



•1002 



•0137 — 



These results substantiate the observations of Gibbs* and of 

 Zimmerman,f and show clearly that the boiling of solutions 

 of the aluminum salt and sodium thiosulphate for a reasonable 

 time does not effect the complete precipitation of aluminum as 

 the hydroxide. 



Table III shows the result of submitting solutions of am- 

 monium alum treated with varying quantities of sodium thio- 



* Loc. cit. f Loc. cit. 



