TIO Professor Fuchs on Opal, and 



Besides amorphous glassy products, of which we have already 

 spoken, many amorphous coagulated bodies are produced in the 

 moist way in chemical laboratories, especially by precipitation. 

 All slimy and gelatinous precipitates are amorphous substances, 

 and many of them when they become dry are resinous or gum- 

 like masses. Some of them emerge gradually from this state, 

 and pass to that of a crystalline powder, by which process they 

 are drawn together into a much smaller space. 



That some of these, by evaporation, and especially by strong 

 heating, become difficultly soluble in solvents otherwise suited 

 to them, may partly be caused by their passing into a crystal- 

 lized condition under such treatment. In relation to this cir- 

 cumstance, the oxides of chrome, of iron, of tin, and of zirco- 

 nium, are particularly remarkable. That tin crystallizes when 

 exposed to a high temperature, is rendered more probable, by 

 the circumstance, that, in its chemical relations, it is identical 

 with the natural oxide of tin, the tinstone. It must also pos- 

 sess the same hardness, as, when it is produced in the dry way, 

 it may be employed to advantage in polishing hard bodies. 

 The same may be said of oxide of iron, since, after being heat- 

 ed, it has the same properties as iron -glance. Mineral Jcermes, 

 in regard to whose nature chemists are not yet agreed, is pro- 

 bably nothing else than amorphous sulphuret of antimony, and 

 merely in this respect different from antimony-glance, into which 

 it is converted by fusion. 



In respect to the capability of possessing form, or to the 

 power of elevating themselves from the state of amorphism, dif- 

 ferent bodies exhibit different phenomena. Some conduct them- 

 selves, under all circumstances, in such a manner as that one 

 might say that they are altogether unable to acquire form ; for 

 example. Water-glass, the Tartarus boraxatus, &c. and several 

 substances already mentioned. 



Other substances lay aside their form only under certain cir- 

 cumstances, and assume it under others, and to this class belong 

 silica, and various bodies capable of vitrification. I might here 

 also name sulphur, which, when heated to a higher temperature 

 than that required for its fusion, and poured into water, imme- 

 diately forms a soft glass, of a dark hyacinth-red colour ; but, 

 after some time, it assumes spontaneously its previous proper- 



