in the drying of a Fluid with Particles in Suspension. 227 



EXPLANATION OF FIGURES (PLATE 2). 



The results shown in figs 1 4 were obtained on glass plates, about 6 inches 

 by 3 inches, with cover- glasses about 3 inches by 2 inches. The whole pattern is 

 represented in figs. 1 3, but fig. 4 shows a small part only of one slide (magni- 

 fied). In each experiment a drop of the mud was placed on the slide, and then 

 covered, so that the mud spread out somewhat irregularly. In other examples 

 similar results were obtained, after running in material or keeping up a current 

 for a short time to carry the mud along. 



FIG. 1. 



Prussian blue in water. This was placed on the glass as a large drop, and a 

 very small one was accidentally deposited near by, in which the pattern at a has 

 been developed. The mud in a few minutes began to show indication of the 

 future pattern. Very shortly the film retreated from two edges (a and 5), where 

 the mud was " denser," and where it dried to a coarse maze. Afterwards the fine 

 maze formed, and was completely developed in two or three days. 



FIG. 2. 



Chalk mass, somewhat thin ; tilted so that the cloudy chalk gradually flowed 

 down. In this pattern the rods tend to become straighter, connected by curved 

 transverse bars. 



(A pattern from denser chalk in several cases, not figured, was that of a coarse 

 maze.) 



FIQ. 3. 



Prussian blue. The fine pattern near one edge (a) with concentric or wave- 

 lines, and some clearer radial furrows was first developed. Then coarser bent 

 stems were deposited, and towards the further margin these became smaller, 

 interrupted, and finally reduced to isolated spots, while the fine material formed 

 rather feathery tufts (less distinct in the photograph). Dried in about two days. 



FiG. 4 (x 8 diameters). 



From a large slide of Vandyke brown, which formed straight axes and a fine 

 c< wave " pattern (an indication of this is shown at one side of the figure). Part 

 of the edge " caked " in drying, and within it, bubbles developed, often elongated 

 transverse to the margin, and stellate cracks or series of cracks. Fine material, 

 somewhat faintly marked in the figure, has formed roughly oval-shaped patches in 

 the vesicles or a central streak in the cracks. 



Note. Certain sharp lines, partly overlapping the pattern in figs. 3 and 4, mark 

 the edge of a film of Canada balsam, by which the cover was sealed down. 



FIG. 5 ( x 25 diameters). 



Mixture of a solution of calcium sulphate and vermilion dried on an ordinary 

 microscope slide beneath a cover-glass. 



The figure represents parts of two long skeleton crystals of calcium sulphate (a 

 and 5) in which a micropegmatitic structure has formed. A small part of a third 

 crystal (c) is shown, the substance of which extends more continuously. The 

 vermilion partly borders the edges of the large skeleton crystals, and is black and 

 opaque in the figure. Other black patches in it are composed of aggregated 

 crystallites of calcium sulphate with some vermilion. The fine scattered lines or 

 radial tufts are similar crystalline needles of the salt. 



