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



these experiments the effect of the same principle on elective affinity can be 

 demonstrated. For this purpose let a small quantity of oxalate of lime, 

 either amorphous or crystalline, be introduced into a microscope-cell filled 

 with a completely saturated solution of chloride of strontium, and securely 

 closed up. On examining such a preparation, the oxalate of lime is seen in 

 a few days to be undergoing disintegration, and new crystals are seen to 

 make their appearance, generally first at the sides of the cell. These 

 crystals being formed slowly have a very sharp outline, and are remarkably 

 transparent. In their form they resemble those obtained by putting 

 oxalate of strontia into a saturated solution of the chloride of strontium ; 

 and notwithstanding that many of them have some of their angles cut off, 

 and are thus made to present additional sides, their composition is precisely 

 the same as if oxalate of strontia had in this instance been acted upon by 

 a saturated solution of chloride of strontium. As in this experiment 

 a chloride of calcium is formed at the expense of some of the chloride of 

 strontium, the solution soon becomes too feeble to decompose the oxalate 

 of lime, when of course the further formation of crystals will cease. Hence, 

 to secure the best results, some crystals of chloride of strontium must be 

 undissolved in the solution when put into the cell. By this means the 

 processes of disintegration and the production of new crystals can be pro- 

 longed for many months, and an opportunity is thereby afforded of mea- 

 suring them, and of determining their rates of increase, or of making such 

 other observations on the subject as the experiment may suggest. 



The methods of forming the double compounds of the oxalates and 

 chlorides of the alkaline earths in microscopical quantities having thus 

 been described, it now remains to show how, on the same principle, these 

 compounds can be formed on the large scale. 



To prepare the double salt consisting of oxalate of strontia and chloride 

 of strontium, it is necessary merely to mix oxalate of strontia (made by de- 

 composing the oxalate of ammonia by chloride of strontium, and washing 

 the precipitate by decantation, and not on a filter) with a solution of chlo- 

 ride of strontium kept at the point of complete saturation. In order that 

 no lumps of oxalate may be mixed with the solution of the chloride, which 

 would be unavoidable if any portion of the oxalate had been allowed to get 

 dry, it is necessary, after finally washing the oxalate, to draw off as much 

 of the water as possible with a siphon, and to add to the mixture of the 

 oxalate of strontia and remaining water the saturated solution of chloride of 

 strontium containing some undissolved chloride. If the solution of the 

 chloride of strontium in which the oxalate is contained is fully saturated, 

 the combination will begin in a few hours ; but it will require two or three 

 weeks before all the oxalate has combined with the chloride. This can be 

 determined only by the microscope. 



The double salt of oxalate of lime and chloride of calcium can be formed 

 in the same manner. In the formation of this compound it is not necessary 

 that the solution of the chloride of calcium should be fully saturated ; and 



