the Disintegrated Surfaces of Crystals. 27 



horaxy tartrate of potash and soda, sulphate of iron, and sulphate 

 of copper-, but though I have delineated many of the figures 

 which they produce, and though some of them have considerable 

 interest, I am not able to present the details in the form which 

 I could wish. I expected to have been able to obtain interesting 

 and definite results by subjecting the faces of a large class of 

 minerals to the action of fluoric acid ; but, in so far as my expe- 

 riments went, I was disappointed. Dr. Fyfe, many years ago, 

 exposed several crystals of quartz and amethyst, which I sent 

 him for this purpose, to the action of fluoric acid, but the disin- 

 tegration of the surfaces was such that they would not reflect 

 any light at all. I have no doubt, however, that by weakening 

 the action and carrying it on very slowly the desired effect will 

 be produced. 



During the preceding experiments I was led to observe, that 

 different solvents had a tendency to produce different figures, 

 and I confirmed the truth of the observation by many experi- 

 ments. When muriatic acid, for example, acts upon alum, it 

 produces a figure with six radiations, not unlike those of sulphate 

 of potash, and by continuing the action, the central image 

 vanishes. If in this state we immerse it in water, three of the 

 radiations vanish, and it assumes the usual form. When again 

 immersed in muriatic acid, the six images reappear. Diluted 

 nitric acid has the same effect as muriatic acid; but diluted sul- 

 phuric acid gives such a form to the radiations, that their extre- 

 mities are included within an equilateral triangle, the larger 

 radiations pointing to the three angles, and the shorter ones to 

 the three sides. 



Diluted alcohol, though it acts feebly upon alum, produces a 

 figure different from water and the acids. It gives a figure with 

 three short radiations; and, by further dilution, the figure 

 undergoes changes which give it a greater resemblance to the 

 aqueous figure. 



In order to retard or diminish the action of solvents upon 

 highly soluble crystals, I conceived the idea of immersing them 

 in solutions of the crystal of different degrees of strength. In 

 making this experiment on alum, I took a crystal which gave 

 the figure shown in fig. 8, and having immersed it in a saturated 

 solution of alum for a single instant, I found that it had, as it 

 were, seized the particles of alum in the solution, and replaced 

 them in their proper position on the disintegrated face. By 

 subsequent immersion the face repassed through all the stages 

 at which it produced the phsenomena shown in fig. 7, and finally 

 became perfect, reflecting a single image of the candle. The 

 singular fact in this experiment is, the inconceivable rapidity with 

 which the particles in the solution fly into their proper places upon 



