PROFESSOR J. W. MALLET ON THE ATOMIC WEIGHT OF GOLD. 
40;j 
General Principles kept in View. 
The improvements made of late years in manipulative methods and apparatus have 
tended to reduce very much the magnitude of what are commonly called “ fortuitous” 
errors in onr quantitative determinations of matter, and to increase greatly the 
accuracy of such determinations. Probably no modern work has had more influence 
in this direction than the classic researches of Stas on certain atomic weights—the 
precautions taken by him, and his remarkable manipulative skill, causing his results 
to bear almost the same relation to those of his immediate predecessors as did those of 
Berzelius to the work of the chemists of his earlier day. No one nowadays would 
undertake the determination of an atomic weight of one of the better known elements 
without taking such elaborate precautions as practically ensure pretty close concord¬ 
ance of results, when obtained by the same method, applied in the same hands. In 
the present state of the cj[uestion of atomic weights and improvements in their deter¬ 
mination, advances in mere delicacy of manipulation and success in merely securing 
close agreement of results by the same method are not alone sufficient. It cannot be 
too much insisted upon that w'e need, besides, well-directed and laborious investigation 
of possible sources of constant errors, and the adoption of means to guard against 
them. Careful preliminary study is required, in a general way, of the precise nature 
of each reaction employed, and how' it may be influenced by the conditions of the 
experiment. We learn more and more of late that many of the reactions—perhaps it 
should rather be said all of the reactions—which have been generally supposed to be 
of the simplest nature are in reality complex. 
The following are among the general principles which seem to be most important, 
as tending to greater accuracy and trustworthiness in atomic w'eight determinations; 
they have been in part stated in the author’s earlier paper on the atomic w^eight 
of aluminum :— 
1. In purifying the materials used, both the element of which the atomic weight is 
to be investigated (or any special compound containing it) and all substances used to 
react thereupon, resort should in all cases be had to “ fractional” methods, assuming 
materials to be pure only wdien earlier and later fractions give no signs of any 
constant difference in the results which they yield. 
2. Different and independent processes should be applied to the determination of 
the same atomic weight, and the results used to check each other. It is desirable 
that as many such diffei’ent processes be applied as can be devised, provided each be 
reasonably free from apparent sources of error, even though it be usually impossible to 
properly assume that all are equally advantageous in this respect, and therefore of 
eciual value. In the comparison of results obtained it should be noticed wdiether a 
given method tends on the whole to yield results probably higher or lower than the 
truth, though it may be gravely doubted whether the practice is commendable of 
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