CRYSTALLIZATIONS. 101 



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 

 seen 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 upod 

 the mimic gems. 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 salient 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 ini- 

 tbrniiy 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 



