Mr GRAHAM'S Account of the Formation of Akoates. 188 



sides of the vessel, which have been moistened by the solution. 

 The solution, however strong, never crystallizes instantaneously, 

 but gradually, in thin transparent and colourless plates, the 

 forms of which cannot be made out, except on the surface of the 

 solution and sides of the vessel. To obtain the alcoate in a 

 state of absolute purity, it is necessary to form a solution so 

 weak, that, while hot, it will pass through thin filtering paper ; 

 and afterwards to concentrate the filtered solution by heat. A 

 solution of one part chloride of calcium in five parts alcohol 

 passes through the filter. It is remarkable that the most distinct 

 crystalline forms are not obtained from the slow crystallization 

 of comparatively weak solutions ; but in solutions which have 

 been fully saturated, or nearly so, at the boiling temperature. 

 In the former case, the crystalline plates are large, but confused, 

 and nothing but angles can be made out ; while in the latter, 

 the forms, under which the plates appear on the surface of the 

 solution, and to the greater advantage, on the sides of the vessel, 

 are generally distinct. These plates are always small, often beau- 

 tiful, and delicately striated ; and they always present the form 

 of isosceles triangles. In general, four of these triangular figures 

 are grouped with their apices together ; and if similar, they form 

 a square. But, as more frequently happens, the opposite pairs 

 of triangles only are similar ; and the figure presented is a rect- 

 angular parallelogram, divided by two diagonal lines into four 

 triangles. The resolution of the rectangle into triangular figures 

 is rendered perceptible by the discontinuance of the striae, and 

 the formation of clear diagonal lines, which have a beautiful ef- 

 fect. These crystals cannot be removed from the phial in which 

 they are formed without injury, from their softness. Exposed 

 to the air, they speedily deliquesce from the absorption of hy- 

 grometric moisture. The heat of the hand is sufficient to melt 

 them. The whole of the alcohol is expelled by a heat amount- 



