CRYSTALLIZATIONS. 103 



SULPHATE OF IRON, OR COPPERAS. This substance crystallizes in transparent, 

 rhomboidal prisms, and appears of a sea-green color when the crystals possess 

 a considerable size. Under the microscope it displays very regular and interest- 

 ing combinations. A drop of an aqueous solution of the sulphate of iron must 

 be only moderately heated, when the film of liquid is soon perceived, crystal- 

 lizing at the edges where it is thinnest ; the principal crystals pushing forward 

 in a straight direction, while at the same time branches proceed from them on either 

 side. These lateral shoots all start from the main crystal at the same inclina- 

 tion, and advance parallel to each other with the greatest precision and order, 

 throwing out likewise secondary branches, which meet and combine ; and the 

 whole array of interlocked crystals, its line bristling with arrow-headed forms, is 

 Been steadily advancing over the field of view. Some of these configurations 

 are massive in their structure, and others more light and delicate ; but all more 

 or less reveal the form of the primitive crystal ; and minute as they are, their 

 solidity is apparent from the mingled lights and shadows that fall upon the crys- 

 tallized surface. And very beautifully are these lights and shadows varied, as 

 the mirror is differently adjusted, and the illumination now plays brightly upon 

 some rich and glittering cluster, and again falls chastened and subdued upon 

 the mimic gems. Drawing 153 represents a group of crystals of sulphate of iron, 

 which, although faithful delineations of actual forms, cannot adequately convey 

 an idea of the rare beauty of the entire crystallized surface. In figures C and 

 D, the regularity of the lateral spurs, branching out from the main stem, is very 

 marked and perfect ; and in E, a broad sheet of lateral crystals proceeds from 

 the principal trunk parallel to each other. At F, three long crystals are seen 

 side by side, with bluntly-pointed heads ; and when under the microscope, the 

 crystallization proceeds slowly, its serrated line is formed of heads like these, 

 which continually advancing into the liquid film, constantly maintain the same 

 shape. At H, a large, heavy crystal, of similar form, is seen, the length of one 

 of whose re-entering side, , 6, is the three hundred and twelfth part of an 

 inch. The last figure, G, is a specimen of a variety frequently beheld amid the 

 crowded mass of crystallizations. Minute crystals, possessing the primitive 

 rhomboidal figure, are sometimes found at the edges of the crystallized film, 

 often clustered together in grotesque combinations, resembling, with their sa- 

 lient points and re-entering angles, the frowning bastions of a fortress. 



CAMPHOR. When camphor is dissolved in alcohol, very elegant crystals are 

 formed upon a slip of glass, by spreading, in the usual manner, a drop of the 

 solution over the surface. 



The film of the fluid crystallizes with great rapidity, owing to the rapid 

 evaporation of the alcohol. When the glass is just prepared and placed under 

 the solar microscope, the image of the drop is beheld upon the screen, as a uni- 

 formly misty surface ; suddenly it is broken up in the thinnest part, which in a 

 moment is studded with beautiful star-like figures. Instantaneous flashes now 

 flit successively over the remaining portions of the cloudy field, and simultaneous 



