FUNDAMENTAL PROPERTIES OF THE ELEMENTS—RICHARDS. 2()] 
include and occlude solvents, precipitates carry down polluting 
impurities, dried substances cling to water, and solids, even at high 
temperatures, often fail to discharge their imprisoned contaminations. 
In the next place, after an analysis has once begun, every trace of 
each substance to be weighed must be collected and find its way in 
due course to the scale pan. The trouble here lies in the difficulty 
in estimating, or even detecting, minute traces of substances remain- 
ing in solution, or minute losses by evaperation at high temperatures. 
In brief, ‘‘the whole truth and nothing but the truth” is the aim. 
The chemical side of the question is far more intricate and uncertain 
than the physical operation of weighing. Yor this reason it is neither 
necessary nor advisable to use extraordinarily large amounts of mate- 
rial. From 5 to 20 grams in each experiment is usually enough. The 
exclamation, ‘‘What wonderfully fine scales you must have to weigh 
atoms” indicates lack of knowledge. The real difficulties precede 
the introduction of the substance into the balance case.1 Every 
substance must be assumed to be impure, every reaction must be 
assumed to be incomplete, every measurement must be assumed to 
contain error, until proof to the contrary can be obtained. Only by 
means of the utmost care, applied with ever-watchful judgment, may 
the unexpected snares which always lurk in complicated processes 
be detected and rendered powerless for evil. 
Among all the possibilities of error, the unsuspected presence of 
water is perhaps the most frequent and most insidious. Hence, I shall 
show you a device for overcoming this potent source of confusion, a 
device which has played a great réle in the recent researches concern- 
ing atomic weights at Harvard, and is in large measure responsible 
for such value as the results may possess. The instrument? enables 
one to dry, inclose, and weigh an anhydrous substance in such a 
manner as to preclude the admission of a trace of water from the 
atmosphere. It might well find applications in every quantitative 
laboratory. The simple device consists of a quartz ignition tube 
fitted to a soft-glass tube which has a projection or pocket in one side 
(fig. 1). A weighing bottle is placed at the end of the latter tube, 
and its stopper in the pocket. The boat containing the substance to 
be dried is heated in the quartz tube, surrounded by an atmosphere 
consisting of any desired mixture of gases. These gases are dis- 
placed after partial cooling, first by nitrogen and then by pure dry 
air, and the boat is pushed past the stopper into the weighing bottle, 
1 Richards, Methods Used in Precise Chemical Investigation, published by the Carnegie Institution of 
Washington, 1910, No. 125, p. 97. 
2 Richards, Zeitsch. anorg. Chem., 1895, vol. 8, p. 267; also Richards and Parker, ibid., 1897, vol. 13, p. 86. 
Two forms of apparatus are shown in this diagram; the upper drawing depicts the earlier form, suitable for 
a hard glass or porcelain ignition tube, whereas the lower drawing illustrates a form slightly different from 
the original arrangement, although the mainideaisthesame. The flat ground joint between quartz and 
glass allows for their different coefficients of expansion, and makes a quartz tube interchangeable with any 
other in case of breakage. 
