38 ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



bination without a stirrer. Could it be possible to construct the last half of 

 the true curve for Dtt by convenient dilutions of the various weak amalgams 

 inside the cell? 



To solve this problem, imagine a series of cells where the concentration 

 ratio is always equal to an arbitrary number 2, for instance. The first 

 cell contains two concentrated amalgams, C x and C 2 , while in succeeding 



7ft 



cells the ratio is expressed in the general form where m is a number that 



m 



can be increased at pleasure. At the beginning of the curve a comparatively 

 small increment of m will produce a measurable change in the Dn of the 

 cell. But far along on the curve, m may be varied considerably several 

 per cent perhaps while Dtt remains sensibly constant. Therefore, if this 

 method of diluting amalgams is used, the true concentration of amalgam 

 C x need not be certainly known within 1 or 2 per cent; the ratio alone is 

 needed exactly when the dilution of the parent amalgam is already great. 

 Some preliminary trials of this method were now made. Pure mercury 

 was drawn into a pipette similar to those used for amalgams, and sealed up 

 without efforts to exclude air. The cell was set up and freed from air as 

 usual, and a known portion of the very dilute amalgam No. 8 run in. The 

 pipette was weighed before and after on a large balance reading at least to 

 milligrams. The rapid succession of weighings made the use of a counter- 

 poise unnecessary. Then a known weight of mercury was run into the 

 same compartment of the cell. The pipettes were tapped before removal 

 from the cell to dislodge loose drops from the capillaries. These were long 

 enough to project into the body of the cell, but they did not touch the electro- 

 lyte. Under these circumstances the loss in weight of the pipette measures 

 the quantity of substance introduced. Two dilutions by this method resulted 

 in the amalgams No. 10 and No. 11, for which the concentration ratio was 

 computed and the electrical measurements made. The densities of No. 8 

 and No. 10 are practically identical. There is no titration correction, of 

 course. 



Quantitative Data. 

 NO. 10. 



Weight of amalgam No. 8, 18.740 



Weight of mercury, 17-442 



36.182 



c ^6.182 . c, 

 ^ = ?874 ;l0!? 4 =0 - 28573 ' 



