418 
PROFESSOR J. W. MALLET ON THE ATOMIC M'EIGHT OF GOLD. 
preventing the strip by which the anode plate was suspended from its clip being cut 
across by solvent action at the surface of the liquid. This coating of paraffine was 
put on after the plates wmre first weighed, and carefully removed before the second 
weighing. The four plates for each experiment were of equal size as to length and 
breadth ; in most of the experiments the immersed surface (of one side) measured 
about 25 square centimetres, though in some cases plates of double this size were 
used. The thickness was the same for plates of the same metal, but those of the 
Fig. 3. 
Fig. 4. 
different metals to be compared were made to differ in thickness to such an extent as 
to allow for the different rate of solution to be expected of the anode plate. I was 
indebted to the kindness of Mr. Eckfeldt, of the Philadelphia Mint, for having plates 
of “ proof” gold and silver specially rolled for me, with all necessary precautions as to 
perfect cleanliness of the rolls, &c., so as to obtain the determinate thicknesses 
desired.'" 
* Mr. Eckfeldt informed me that his method of preparing the proof silver used for these plates was as 
follows:—“Nitrate of silver from the gold assay pai-ting is, after careful filtering, precipitated with 
