PROFESSOR J. W. MALLET ON THE ATOMIC WEIGHT OF GOLD. 
401 
The general mean of these values, giving equal weight to the different series, is 
196-852. 
As regards possible sources of constant error specially belonging to these experi¬ 
ments, it is to be noticed-^ 
1. There is an advantage, as observed by the authors themseivms, over the greater 
part of the experiments of Kruss in the nature of the relations employed not requiring 
that the potassium anri-bromide should be perfectly dry, the exact quantity of the 
orio-inal salt not needing’ in fact to be known. 
2. In series a it is conceivable that there might have been slight volatilization of 
potassium bromide, or interchange in it to a small extent of bromine for oxygen, 
during the heating of the original salt, or retention of traces of potassium bromide by 
the metallic gold when washed—the latter but little probable. Any of these defects, 
if existing, would cause the method to give a higher value for Au than the true one. 
3. In series h the pi’obability seems to be in favour of not quite the whole of the 
original potassium bromide being actually used, arid minute loss of silver solution 
having perhaps occurred, so that rather more of this solution was counted as used 
than the true quantity, If so, the former defect would tend to raise, the latter to 
lower, the atomic weight of gold. 
4. In series c, in view of the evidence adduced to prove complete drying of the 
silver bromide, it is more likely that its weight as obtained was below, rather than 
above, the truth. Hence we should suspect, if any constant error exist, that it would 
rather tend towards an unduly high value for Au. 
On the whole, there seems to be less reason to fear sources of constant error of any 
considerable amount in connection with the experiments of Thorpe and Laurie than 
with those of Kruss, and the drift is in the opposite direction, tending rather to give 
too high than too low a value for the atomic weight to be determined. 
It should be mentioned that Kruss’"' has claimed that in the potassium auri-bromlde 
used by T'horpe and Laurie there was probably as much free gold as he considered 
to exist in the salt used by himself, and on this assumption has calculated that the 
three series of experiments by the English chemists should, if corrected on this 
account, lead to the niimliers 196-616, 196-5,59, and 196-575 respectively for Au. 
From this conclusion the latter chemists altogether dissent,! and express their con¬ 
fidence that in none of the preparations used by them was there fi’ee gold sufficient to 
account for the difference between their own results and those of Kruss. 
* ‘ Berichte Deutsch. Chem. Gesell.,’ vol. iJO, p. 2365. 
t ‘ CLem. Soc. Journ ,’ Dec., 1887, p. 868. 
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MUCCCLXXXIX.—A 
