OF MICROSCOPIC OBJECTS. 75 



t 



following process ; but the uncertainty is increased a little when 

 fusion is used, which, however, is desirable with many salts. 

 Secondly, mate a saturated solution of salicine, which in cold water 

 is effected by adding one part of the salt to eighteen parts of water. 

 Lay a little upon the slide, and allow it to evaporate spontaneously, 

 or with the aid of gentle heat. The crystals are generally uniform, 

 and with ordinary powers quite large enough to afford a beautiful 

 object. The circular shape and gorgeous colours of this crystal 

 have made it so great a favourite that there are few cabinets with- 

 out it. 



Many new forms may be procured by uniting two totally dif- 

 ferent salts in solution in certain proportions. This is a field af- 

 fording new facts and beauties; but requires some chemical know- 

 ledge and much perseverance to obtain very valuable results. One 

 of the most beautiful I have met with has been composed of sul- 

 phate of copper and sulphate of magnesia. The flower-like forms 

 and uniformity of crystallization when successful make it well 

 worth a few failures at first ; and as I became acquainted with 

 some new facts in my frequent trials, I will give the preparation 

 of the double salt from the beginning. 



Make a saturated solution of the two sulphates, combined in the 

 proportion of three parts copper to one part magnesia, and then 

 add to the solution one-tenth of pure water. Dust or other im- 

 purities should be guarded against, and the slide made free from 

 all trace of grease by cleaning immediately before x use with liquor 

 potassse or ammonia. A drop of the solution should then be placed 

 upon the slide, and by a thin glass rod spread evenly upon the 

 surface. Heat this whilst in a horizontal position until the salt 

 remains as a viscous transparent substance, which will not be ef- 

 fected until it is raised to a high degree. The slide may now be 

 allowed to cool, and when this is accomplished, the flower-like 

 crystals will be perceived forming here and there upon the plate. 

 When these are at any stage in which it is wished to preserve 

 them, a few seconds' exposure to the fire, as warm as the hand 

 can comfortably bear, will stop the expansion, when the portion 

 which we wish to mount should be cut off from the mass of salt 

 by simply scratching the film around, and pure Canada balsam 

 with the thin glass used. Breathing upon the film, or allowing 



