PROPERTIES OF SALINE SOLUTIONS — MACGREGOR. 75 



must be added as a shower of line powder, as larger pieces 

 may by taking up water and forming crystals of the hydrated 

 salt before they can dissolve, give rise to a general crystalliza- 

 tion of the solution. 



(4.) The peculiarity of the solubility in water of such sub- 

 stances as anilin, carbolic acid, etc., observed by Alexejew,* may 

 readily be shown on the screen, by using carbolic acid, whose 

 critical temperature (the temperature above which it and water 

 are nuitually infinitely soluble) is about 69° C. For this pur- 

 pose, pour some of the acid into a long test-tube, of about 12 or 

 15 mm. diameter, and add water. The water will lie in a layer 

 above the acid. Support the test-tube by a clip grasping it at 

 the top, and focus on the screen. The line of demarcation 

 between the two liquids will be evident. Now mix the liquids 

 by stirring, and the whole becomes cloudy. Let the tube stand, 

 and the liquid separates again into two layers, having different 

 depths from those they had before, both being now solutions. 

 As this process re(:[uires considerable time, the stirring may have 

 l)een done beforehand. Next surround the test-tulje by a beaker 

 of boiling water, passing it upwards from Ijelow, and stir the 

 licjuids with a hot glass rod. A slight cloudiness appears, Itut 

 the licjuid quickly clears and is seen to have become homogenous 

 throughout, the line of demarcation having disappeared. If now 

 the beaker of hot water be removed, and one of cold water be 

 substituted for it, the liquid becomes cloudy, a strong solution 

 Separating out everywhere, and the little spherical masses of 

 strong solution sinking and coalescing as they sink, to form 

 larger spheres. After a time the liquid is seen to have again 

 become separated into two layers. If the necessary time is not 

 available, the separation into layers may be obtained very quickly 

 l)y removing the beaker of cold water and again applying the 

 hot bath, which, raising the temperature, stops the separating out 

 of the strong solution and re-dissolves it in the surrounding- 

 weaker solution, thus producing a comparatively strong solution 

 in the lower part of the tul)e and a comparatively weak one in 

 the upper part. The experiment requires Ijut a few minutes 

 and is both striking and instructive. 



♦ Wied. Ann. Bd. XXVUI. (li:86), p. 305. 



