20 



ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



The apparatus thus arranged and scrupulously clean and dry is manipu- 

 lated as follows : First, S x , S 2 , and S 5 are closed, and S 3 , 6" 4 , and 5 6 left 

 open ; the pressure in B and F is reduced to I or 2 cm. of mercury, after 

 which the rubber tube V is clamped off beyond M to test for leakage. If M 

 remains at exactly its original height for one minute it is assumed that no 

 leakage occurs. Then S 3 is closed, and S t cautiously opened, filling the 

 system with hydrogen. This operation is performed three times, after 

 which the air in the capillary C is expelled by a stream of hydrogen. Then 

 S 5 and S i are closed, and S s opened, exhausting F once more; the tube C 

 is then plunged below the surface of the amalgam under ammonia in the 

 weighing tube, and S 5 cautiously opened. In this way all the amalgam can 

 be sucked into the flask practically free 

 from moisture. As the last of it 

 passes S- a the flow is stopped. Main- 

 taining a low pressure in F, a rapid 

 stream of hydrogen gas is bubbled 

 through the amalgam to mix it and to 

 eliminate the last traces of water and 

 ammonia. After five or ten minues S z 

 is closed, and F filled with hydrogen; 

 S t and S 4 are closed and B evacuated 

 through So. Then S i is cautiously 

 opened, and the amalgam sucked into 

 B, filling not more than 10 per cent of 

 the entire volume. The vacuum is 

 now shut off, and B filled with hydro- 

 gen communicating with the outside 



air through S 2 . The tube A can now be sealed off from the generator with- 

 out admission of air. Its end is bent into a hook to allow of suspension 

 from a balance. Tube D is cut with a file, and B detached from F. The 

 pipette is labeled and placed in a rack with its fellows (figure 3). The 

 ammonia in C is added to the main portion in the weighing tube, and titrated 

 as before described. 



Amalgams prepared in this way are perfectly clean and bright and remain 

 so indefinitely. The weight of the column in the outlet tube permits the 

 withdrawal of practically all the amalgam when the stopcock is opened. 

 No access of air is possible except at the very small surface at the end of 

 the capillary E, and even this small effect can be eliminated by running out 

 a drop of amalgam before beginning a determination. 



The solution of zinc or cadmium sulphate was freed from air in the appa- 

 ratus just described. The liquid was introduced into the flask F like an 



Fig. 3. Rack with Pipettes 

 Containing Amalgams. 



