36 



A series of models, showing the typical forms found 

 in each class, were exhibited at the conclusion of the 

 Lecture. 



Of the formation of crystals in the earth but little is at 

 present known, and the report of work done in the laboratory 

 to interpret this portion of the book of Nature is so laden 

 with technicalities that it will not bear abstraction with 

 advantage. 



This, however, we must remember, that the more slowly 

 a crystal is grown, the finer the crystal obtained ; and we, 

 feebly imitating Nature, have but a brief time to effect our 

 experiment ; consequently, to obtain in one year, month, or 

 week the result yielded in Nature's laboratory by an age's 

 growth, we must compensate for the shortness of time by 

 proportionately increasing other conditions of experiment — a 

 necessity fraught with the greatest difficulty. 



The specimens of natural crystals exhibited are very 

 large and fine— the results of gradual growth — compared with 

 those which can be obtained in an evening ; still, it is not 

 altogether impossible that even the diamond may be grown 

 by artificial means, though the success attending attempts 

 to produce it has been at present but small. 



Water, united with other substances, plays a most 

 important part in determining the colour, and even the form, 

 of their crystals. 



On taking some of the large blue crystals of Sulphate of 

 Copper, powdering them roughly, and introducing them into 

 a glass retort, we find, on applying heat to the vessel, that 

 the crystals split and steam rises from them, passing down 

 the neck of the retort, and condensing as clear water in the 

 receiver. At the same time the blue crystals crumble, and 

 lose all geometrical shape, becoming almost white. Chemical 

 examination proves that the only difference between the fine 

 blue crystals and the white amorphous powder is, that the 

 former is Sulphate of Copper, with water in combination ; 

 the latter, Sulphate of Copper deprived by heat of the water 

 previously held in combination. 



i 



