1878.] the Function of the sides of the Vessel, fyc. 191 



have little or no effect on solutions of sodic sulphate and sodic acetate. 

 The most satisfactory results were obtained with magnesic sulphate ; 

 but with this and other solutions the results varied with the state of 

 the weather as the crystallising force varied, and also with the nature 

 of the rubber, whether a glass rod or the wires just named. 



At lene-th it occurred to me to line the tubes with some substance 



o 



which is not wetted by the solution or imperfectly so. Accordingly, 

 two large tubes (5 oz. and 3 oz.) were made chemically clean, and 

 coated with a solution of amber in chloroform. They were three parts 

 filled with a solution of sodic sulphate (2 to 1), covered over, and left 

 until the next day. A stout platinum wire was taken out of hot 

 water and introduced into each tube, when moderately hard friction 

 was made in a vertical line about one-sixth or one-eighth of an inch 

 in length. A crystalline brush immediately diverged from the part 

 rubbed,' and spread all through the solution, the mass of which was 

 sufficient for the eye to note the details, and to convey the assurance 

 that crystallisation set in from the part rubbed and from that only. 



The advantage of using amber is that the coating, being transparent, 

 allows the progress of the experiment to be watched. The same 

 advantage may, however, be obtained at less cost and trouble, by 

 means of resin, a small quantity of which, in powder, together with a 

 few drops of spirits of wine, heated in the tube over a spirit lamp, 

 enables the operator easily to spread a coat evenly upon the inner sur- 

 face by moving the tube about while it is still warm. 



A number of one-ounce tubes, coated in this way, were filled with a 

 stronger solution of sodic sulphate (3 to 1) than that before employed. 

 The result was satisfactory : the solutions often became solid in cool- 

 ing, and always when the inner surface was rubbed with the platinum 

 wire. 



The experiment was also made comparative by placing an uncoated 

 by the side of a coated tube, and so leaving them to cool covered with 

 glass capsules, or small beakers. The solution in the coated tube 

 often solidified in cooling, and always remained liquid in the uncoated 

 tube, 



The results as obtained with supersaturated solutions of other salts 

 also showed how greatly they depend for their stability on adhesion. 

 The system always broke down when a portion of the solution was 

 detached from the side, by the rubbing action of the wire. The solu- 

 tion of each salt, however, presented those characteristic features of its 

 own, which form one of the principal charms in the study of natural 

 objects. In the ammonia alum solution (1 to 1) the octohedral crystals, 

 under the action of rubbing, seemed to bound forth towards the axis 

 of the tube. In the magnesic sulphate solution (3 to 1) the disengaged 

 crystals were too minute to appear, except as a chalky-white line fol- 

 lowing the motion of the wire. Zincic sulphate (3 to 1) formed small 



