1865.] Double Chlorides and Oxalates. 153 



late employed in this experiment had been prepared by exposing to the 

 action of boiling oil an amorphous oxalate of strontia, precipitated from 

 its combination with chloride by means of water. This precipitate not 

 containing any octahedral crystals, and being acted upon more speedily 

 by water than the other forms of anhydrous oxalate of strontia, is best 

 suited for the demonstration of the effect above described. The oxalate of 

 lime which had been subjected to the action of boiling oil and kept in distilled 

 water had not undergone any visible change. I may notice, in reference to 

 some oxalate of strontia which had been heated in boiling oil and exposed to 

 the air for five or six weeks, that the action of water upon it was diminished, 

 but was entirely restored after a second exposure to the heated oil. 



In reference to the cause of these changes from the amorphous to the 

 crystalline form by the mere action of water, it is evident that, as they 

 take place in perfectly closed cells, and commence in so short a time after 

 the introduction of the amorphous oxalate and water, they are inde- 

 pendent of evaporation or of alteration of temperature. Hence they seem 

 to be simply the effect of the chemical union of the water with the anhy- 

 drous oxalate to form a hydrous oxalate, which, being presented to the 

 action of the water in the cell on the instant of its formation, is dissolved 

 in a larger quantity than can be retained in solution, and thus whilst 

 one portion of hydrous oxalate is being formed and dissolved, that which 

 was formed previously is in the act of being deposited, and thus these 

 processes go on simultaneously until all the amorphous oxalate which 

 was introduced into the cell is changed into well-defined crystals, as was 

 before explained in treating of the compound salt of the oxalate and 

 chloride of strontium. 



In conclusion I may add that the oxalates are not the only compounds 

 of the alkaline earths which form double salts when brought into contact 

 with strong solutions of chlorides of the same base. Crystals of tartrate 

 of lime put into a saturated solution of chloride of calcium, form a double 

 salt of tartrate and chloride of calcium, which is decomposed by water into 

 tartrate of lime and chloride of calcium. Also the carbonate of lime, 

 under favourable circumstances, will combine with the chloride of calcium 

 to form a double salt which is acted upon by water, in the same manner 

 as those above treated of. To obtain this last-named compound, it is 

 necessary to put crystals of carbonate of soda or potash into a relatively 

 large quantity of a saturated solution of chloride of calcium, so that the 

 carbonate of lime, immediately on its coming into existence, may be acted 

 upon by a solution of the requisite strength. Solid particles of carbonate 

 of lime, whether crystalline or globular, are not affected by a saturated 

 solution of chloride of calcium. Without doubt these experiments might 

 be so modified and extended as to embrace other substances which are of 

 very different degrees of solubility, and which still do not decompose one 

 another; but as there is no apparent limit to such a course of experiments, I 

 must now conclude my communication, hoping that the (in some respects) 



