268 Experiments in Crystallization. 



acid, and eight parts of water, beautiful large groups of crystals 

 will appear. The acid should not be allowed to remain in 

 contact with the metal, but quickly washed off with water. 

 Dark spots may be generally removed with a little caustic 

 potash. 



By sprinkling the surface of the heated tin with cold water, 

 or by acting upon portions of the surface with the blowpipe, 

 great variations in the pattern may be obtained. As M. Kuhl- 

 mann states, any point touched by a cold water drop 

 becomes the centre of a crystalline pattern, the rays from which 

 proceed until they are arrested by similar rays proceeding from 

 other centres. The lustre of these patterns may be preserved by 

 a coat of transparent varnish. M. Kuhlmann considers that 

 the variations which these crystals present from the normal 

 crystallization of tin, result from the action of the iron in the 

 tin plate, which offers certain obstacles to the crystalline force. 



There is, to our apprehension, very little originality in 

 M. Kuhlmamr's remarks, as experimenters have long recog- 

 nized the effects of substances which modify the power and 

 direction of crystalline forces ; but though we see no novelty in 

 his philosophy, we may borrow some of his illustrations, with 

 thanks for their suggestion. He tells us that, if we remove 

 all grease from a plate of metal or glass by means of potash, 

 and then wash it over very lightly with a solution of mannite, 

 we shall obtain, as it evaporates, a pattern composed of stars, 

 separated from each other by straight lines at equal distances 

 from the centres of radiation. The solution of mannite must 

 not be too strong. 



By covering a clean glass plate with strong solution of 

 sugar, he obtained a varnish which did not alter after several 

 days exposure to dry air; but which, being left for one day 

 in a damp cellar, exhibited a new appearance, the sugar 

 having arranged itself in groups of crystals, leaving blank 

 and uncovered interspaces on the glass. In this case the 

 moisture had given sufficient mobility to the sugar particles 

 to permit their arrangement by the crystalline force. 



On covering clean plates of glass or metal with solutions 

 of sulphates of iron, copper, zinc, and many other substances, 

 vacant spaces were left when the crystallization was free; 

 but if the mobility of the particles was lessened by the 

 presence of metallic oxydes, alumina, or magnesia, or by an y 

 gummy, gelatinous, or albuminoid substance, the crystals 

 extended over the whole surface occupied by the solution, 

 and beautiful effects in the shapo of stars, garlands, etc., 

 were produced. 



M. Kuhlmann says that all viscid substance-, such 

 gums, dextrine, albumen, gelatine (sugar, and glycerine ex- 



