26 
PROFESSOR W. A. TILDEX AND MR. W. A. SHEXSTOHE OX THE 
arranged so that after draining the solution from the residual crystals it was shut off 
in a portion of the tube of known capacity, further entrance or escape of vapour being 
prevented, the risk of an impoverished solution continuing to drain into it during 
cooling being also done away with. But though we were successful in getting such a 
tube constructed, the difficulty of working it and of keeping it in working order, led 
us to abandon it in favour of a simpler form. 
4. The influence of pressure.—Mr. Sorby’s experiments (Proc. Boy. Soc., xii,, 538) 
show that pressure exerts an influence upon the solubility of salts in water, but the 
effect due to the pressure existing at high temperatures in our tubes is too small to 
affect materially these estimations of solubility. In our experiments, with only two 
or three exceptions, the pressure of the vapour in the tube could never have exceeded 
some 10 or 12 atmospheres. 
5. The choice of salts at our disposal is more limited than might be expected.—In 
some cases the solubility becomes so great at temperatures above 100°, that quan¬ 
titative experiments were found to be impracticable. In others, as may be supposed, 
water at high temperatures decomposes the salts with formation of precipitates, or 
other signs of chemical change. 
In one case, namely, chloride of barium, the crystals of the salt fall to a powder, 
from which it was found impossible to withdraw the solution. 
6. We intended originally to have made a much larger number of determinations 
at temperatures above 200°, but it was not found practicable, partly in consequence 
of the difficulty of maintaining constant so high a temperature in the air bath (and 
paraffin could not be used), partly because the pressure at 250° and above becomes 
so considerable (amounting probably to about 30 atmospheres), that the lead washer 
in the joint of the metal tube was forced out, no matter how tightly the parts were 
screwed together. 
The melting point of the most fusible salt tried (silver nitrate, m.p. 217°), is easily 
reached, but its solubility at temperatures far below this was so excessive that further 
determinations became impossible. 
The apparatus finally adopted is represented (half-size) in Plate 1, figs. 1 and 2. 
The tube is made of gun metal, electroplated with silver all over. The two parts screw 
together at C. Each of the faces, b, b, b', b', has two circular grooves cut in it, an 
electroplated lead washer fits between these two faces, and when the proper amount of 
pressure is applied in screwing up, the lead is forced into these grooves. Plate 1, 
fig. 1 b, shows the end of B. It is hexagonal for convenience in screwing up. a, a , 
is a disk or screen of silver having a semicircular opening, e, cut through it. When 
the tube is closed, a does not quite touch f. By means of the handle h, the tube may 
be turned round its longitudinal axis in its support during an experiment, so that 
liquid may be free to flow from A to B through e, or not, as may be desired. In using 
the tube the materials are placed in A, a disk of platinum gauze is placed above at 
about g, and the two parts are screwed together very firmly. The tube is then placed 
