152 Mr. Rainey on the formation of [Mar. 30, 



Before concluding this part of my subject, I have a few observations to 

 make on the oxalates of the alkaline earths produced by the sudden action 

 of water in sufficiently large quantity upon their double salts, especially 

 those of the double salts of strontia and baryta. 



For this purpose it is necessary only to drop a few well-formed crystals of 

 the double salt of oxalate of strontia and chloride of strontium into a test- 

 tube filled with distilled water, when they will be seen instantly to become 

 opaque. The general form of these crystals remains more or less complete, 

 but their interior is filled up with entirely amorphous oxalate, especially in 

 the very thin crystals. If some of the crystals thus acted upon be put into 

 distilled water in a microscope-cell perfectly closed to prevent the escape of 

 the fluid by evaporation, and examined from time to time with a i-inch lens, 

 they will be seen gradually to go into well-defined octahedral crystals, 

 some months being required before the whole of the amorphous oxalate is 

 converted into crystals ; but all specimens thus prepared are not acted upon 

 by water to the same degree. Among several slides showing this fact, I 

 have one in my possession dated May 20th, 1863, in which the whole of 

 the amorphous oxalate introduced has become transformed into remark- 

 ably beautiful and well-formed octahedral crystals, many of them of large 

 size, considering that they had been formed in so small a quantity of water 

 the mere fraction of a drop. Some portions of this oxalate remained 

 unchanged for more than a year after it was put into the cells, but the 

 whole of it has since been converted into perfect crystals. As the effects 

 of water upon these forms of oxalate are not uniform, it was considered 

 necessary first to determine whether it was only on the oxalate as above 

 prepared that water caused these changes, or whether it was not a ge- 

 neral consequence of the action of water upon sparingly soluble salts, 

 rendered amorphous in consequence either of a complete absence of water, 

 or of an insufficiency for perfect crystallization (the sudden action of the 

 water upon the double salt separating the chloride from the oxalate more 

 rapidly than the water of crystallization could combine with it) ; and with 

 this view the following experiments were performed. The oxalates of lime, 

 strontia, and baryta, all made by precipitation in the usual way, were ex- 

 posed, for the purpose of expelling the water of crystallization, in small 

 test-tubes to the temperature of boiling oil for three or four hours, and 

 afterwards put into closed microscope-cells with distilled water. On ex- 

 amination with the microscope, it was found that the oxalate of baryta 

 had begun in a few hours to pass into a more minute state of division, and 

 that on the same day octahedral crystals could be seen by a ^-inch lens ; 

 and in the space of six weeks nearly all this oxalate had become trans- 

 formed into regular octahedral crystals. The oxalate of strontia had un- 

 dergone a similar change, but rather more slowly ; distinct octahedral 

 crystals, however, were visible in twelve hours. 



As the oxalate of strontia obtained by precipitation in the usual way 

 generally contains some octahedral crystals, some of the amorphous oxa- 



