120 Norton — Action of Sodium Thiosulphate on 



the formation of normal chromate. A solution of potassium 

 chromate is unaffected by boiling with thiosulphate, but in 

 presence of ammonium or of magnesium chloride the chro- 

 mium is separated rapidly and completely in the same form 

 as with the bichromate, and after continued boiling with an 

 excess of thiosulphate all the chromium present is precipitated. 

 Faktor also found that a solution of chromic chloride is com- 

 pletely decomposed by continued boiling with thiosulphate, 

 chromic hydroxide and sulphur being precipitated. 



In the experiments shown in Table IV a weighed quantity 

 of pure potassium bichromate was dissolved in water, a known 

 amount of sodium thiosulphate added, and the whole submit- 

 ted to a pressume of 20 atmospheres in the digester. After 

 cooling, the precipitate was filtered off on an ashless paper,, 

 ignited and weighed as Cr 2 3 . 





Table 



IY. 





K2O2O7 taken 



Amount of 







as Cr 2 3 . 



Na 2 S 2 6 . 



Cr 2 3 found. 



Error. 



grms. 



grms. 



grms. 



grms. 



1. -.1330 



3 



•1341 



•0011 + 



2. '1330 



2.5 



•1326 



•0004 - 



3. '1322 



2-5 



•1318 



'0004 + 



4. '1303 



2 



•1303 



•0000 — 



5. '1301 



2 



•1310 



•0009 + 



6. '1320 



2 



•1322 



•0002 + 



The results of these experiments are very satisfactory and 

 show that under pressure sodium thiosulphate precipitates 

 chromium rapidly and completely as the hydroxide. It is 

 advisable to use as small a quantity of thiosulphate as possible 

 in order to prevent the presence of much free sulphur in the 

 precipitate. 



Experiments with a Salt of Beryllium. 



In experiments dealing with beryllium the salt used was the 

 chloride, a certain amount of which was dissolved in water 

 diluted to a liter and the amount of beryllium present deter- 

 mined by precipitating with ammonia and weighing as the 

 oxide. Measured quantities of this solution were drawn from 

 a burette as required. When a solution of a salt of beryllium 

 and sodium thiosulphate are merely boiled together, nearly all 

 the beryllium remains in solution. It was expected that the 

 use of pressure would throw out all the beryllium, but, curiously 

 enough, when solutions of beryllium chloride and sodium thio- 

 sulphate were submitted in the digester to pressures ranging 

 from 10 to 80 atmospheres, only a partial precipitation of the 

 hydroxide took place. 



