1824.] Mr. Cooper on the Nitrates of Strontia. 289 



Article XIII. 



Analysis of the Nitrates of Strontia, described in the preceding 

 Paper. By Mr. J. T. Cooper. 



(To the Editor of the Annals of Philosophy.) 



DEAR SIR, March 20, 1824. 



At the request of Mr. Brooke, who observed the difference 

 in the primary forms of the crystals of this salt, 1 have under- 

 taken its analysis, and for this purpose I exposed 50 grains of 

 the prismatic variety to a heat of 240° Fahr. for a considerable 

 time until it ceased to lose weight ; the quantity of water lost 

 was 13-9 grains, leaving 36-1 of dry nitrate ; the dry nitrate was 

 then dissolved, and solution of carbonate of potash added (of 

 known strength) until it ceased to precipitate carbonate of stron- 

 tia ; it required a quantity of the solution equal to 23*8 of 

 dry carbonate of potash ; the fluid portion now showed no trace 

 of the alkali, or the earth. The carbonate of strontia, when dry, 

 weighed 25*7, and the fluid portion evaporated to dryness left 

 34*7 of nitrate of potash. 



From the above, it is evident the composition of prismatic 

 nitrate of strontia is in 50 grains 



Acid 18-4 or in 100 30-8 



Base 17-7 35-4 



Water 13-9 27-8 



50-0 100-0 



This differs considerably from Kirwan who, appears to be the 

 only chemist who has examined this variety : he states the com- 

 position of it as, 



Acid ; 31-07 



Base 36-21 



Water 32-72 



The difference in the quantity of water may be in a great 

 measure accounted for by his not selecting perfectly formed 

 crystals for his experiments ; but how the variation in the pro- 

 portions of the acid and base could arise is much more difficult 

 to account for. The crystals employed by me were selected by 

 Mr. Brooke for the purpose. 



I also obtained from Mr. Brooke some well-formed crystals of 

 the octahedral variety, and having weighed 14-84 grains, 1 sub- 

 jected them as before to heat for a considerable time ; the loss 

 amounted to -07 : they were afterwards heated to a much higher 

 temperature, but not sufficient, to decompose the salt, when a 



New Series, vol. vii. u 



