400 
and is something reserved for the use of 
those with chemical leisure on their hands, 
that our progress toward better things is 
so slow. It is also the reason why a great 
deal of time is wasted on procedures which 
are almost without value as soon as any 
one of the particular conditions (often 
very far from practical conditions) under 
which they were tested, is altered. It is 
not at all a difficult matter to obtain an 
understanding of at least the meaning, for 
example, of chemical equilibrium and the 
laws which apparently underlie equilibrium 
phenomena; yet there are instances of the 
publication of processes recommending 
procedures in defiance of these principles, 
and a great deal of time is wasted in pri- 
vate because of ignorance of them. An in- 
teresting and fruitful application of these 
principles is to be found in connection with 
the processes of neutralization and hydrol- 
ysis, and in selection of suitable indicators 
for use with acids and bases of varying 
strength. Modern research has changed 
this from a haphazard procedure to one of 
comparative exactness. The principles are 
not difficult to, follow and, if once mastered, 
ean not fail to render any subsequent work 
in this field more intelligent and, therefore, 
more pleasurable. 
The phenomena of adsorption, with 
their attendant annoyanees to the analyst, 
have been widely studied. The results are 
perhaps less positively helpful than in the 
ease of the indicators, but the material is 
nevertheless well worth attention and 
study. Colloids—which probably play an 
often unsuspected part in our analyses for 
‘good or ill—must not be overlooked by the 
well-informed chemist who would best 
economize his time and energies, and the 
simple matter of the best way to wash a 
filter and its contents, long ago pointed out 
by Ostwald, are not as familiar as they 
should be. The spectroscope and micro- 
SCIENCE 
[N.S. Vou. XXXV. No. 898 
scope are more useful than formerly, a 
system of micro-analysis, both qualitative 
and quantitative, having been developed 
with the latter instrument; the ultramicro- 
scope may well open up new lines of study 
with respect to the formation of precipi- 
tates, the existence of colloids or the condi- 
tions controlling electrolytic deposition; 
wash-waters may now sometimes be advan- 
tageously tested through their electrical 
conductivity; the refractometer, the ne- 
phelometer, the colorimeter, the centrifuge, 
are all finding extended usefulness, and it 
is incumbent upon the analyst to under- 
stand these instruments, and their under- 
lying principles thoroughly if he is to fully 
avail himself of their aid. 
It is probable that analytical chemistry 
has been as directly aided by the increased 
accuracy of solubility determinations as in 
any other way; and these have largely been 
made practicable by the development of 
the physico-chemical methods of measure- 
ment. These determinations have made it 
possible to judge of the greatest attainable 
accuracy of a precipitation method, and 
have also made practicable the use of a cor- 
rection factor in the case of unavoidable 
losses. The analyst should no longer con- 
tent himself with the mere thought that 
such losses are inevitable until he has defi- 
nite assurance that data sufficient to permit 
of a reasonably accurate estimation of these 
losses are not to be found. The values ob- 
tained for the solubilities of the various 
sulphides, which are much more accurate 
than those formerly available, have alone 
done a great deal to enable the working out 
of a more reliable scheme of qualitative de- 
tection of the elements, one which is based 
on scientific deductions, confirmed by care- 
ful experimentation, as, for example, in the 
separation of the sulphides of arsenic, 
antimony and tin by hydrochloric acid, the 
separation of zine from the metals of the 
