1865.] Double Chlorides and Oxalates. 145 



various compounds I am about to treat of can be most easily prepared in 

 minute quantities, and afterwards those by which they can be formed in any 

 quantity that may be required. 



All the apparatus necessary for the preparation of these compounds in 

 quantities sufficient for microscopical examination, are a few cells made by 

 cementing a ring of thin glass, such as is ordinarily used by microscopists,, 

 and some circular disks of thin glass to be employed as covers. The cell 

 must be sufficiently shallow to allow of the examination of its contents with 

 a lens of a half or quarter of an inch focus. 



To prepare the compound of oxalate and chloride of strontium, introduce 

 into a cell a few crystals of oxalate of strontia, and add to them as much 

 saturated solution of chloride of strontium as will completely fill the cell ; 

 then cement upon the cell a thiu glass cover in such a way that the cell 

 shall be completely air-tight. A cell thus charged must be kept in a 

 horizontal position, and examined from time to time. In a few hours the 

 angles and edges of the oxalate of strontia crystals will be observed to hare 

 lost their sharpness of outline, being in a state of disintegration, and very 

 minute crystals, altogether of a different form from those of the oxalate, to 

 have made their appearance ; and on successive examinations all the octa- 

 hedral crystals will be seen to have disappeared, and to have become re- 

 placed by exceedingly well formed rhomboidal crystals of different sizes, 

 composed of the two salts introduced into the cell. (Fig. 1.) In this ex- 

 Fig. 1. 



periment the solution of the chloride of strontium must be fully saturated ; 

 and if it even contain a few undissolvod crystals, the processes of disinte- 

 gration of the oxalate, and formation of the compound, will be prolonged, 

 and more time allowed for their microscopical examination. 



If, in the place of oxalate of strontia and chloride of strontium, crystals 

 of oxalate of lime, and a strong solution of chloride of calcium be intro- 

 duced into a microscope-cell, and the cell be closed up, the crystals of this 

 oxalate (like those of the oxalate of strontia) willbeseen by the microscope 



