154 



tOMPOSITION OF SULPHATES. 



100 parts of alum; such an increase in the quantity of 



materials could not fail to engage ray attention, and lead 



me to seek the cause of so great a difference between the 



results of analysis and those of a manufactory on a large 



scale. At first J suspected, that the surplus of acid and 



potash I employed entered into the composition of the 



An insiiiubie insoluble sulphute of alumine, which, I have remarked, 



sulphate of is sometimes formed. Indeed [ was long induced to en- 



atuotine some- ,.,... .1.1 . , 



tiiiies foimed. Certain thts opinion, rather than suppose, that the quantity 



of acid and of potash entering into the composition of 

 alumine were more considerable, than had been fixed by 

 different analyses, on the accuracy of which I had always 

 depended. 

 TtK&i#*lfn However, admitting the hypothesis of the constant for- 

 prereirt ttfis. mation of an insoluble sulphate of alumine, I could not 

 remain indifferent to the loss of this substance: on the 

 contrary, it was an object with me to find the means of 

 preventing the alum from passing to this state of insolu- 

 bility. Accordingly, as soon as I was certain, that all the 

 acid and potash employed entered into the composition of 

 the alum I manufactured, I was convinced, that my former 

 observations had been just. 

 Attempt to But as I was not satisfied with being merely convinced 



ascertain the Q f w \ Vd i was i n favour of my observations, it remained for 



proportions of .... . , . , 



potash and acid oie to ascertain by direct experiments, and particularly 

 in alum. sac h as cou ld easily be repeated, how much acid and 



potash enter into the composition of alum. I wished also 

 to learn, whether the quantities of acid and base in the 

 sulphate of potash were such, as are generally admitted. 

 Lastly, that my experiments might not be suspected of 

 the least inaccuracy, it became necessary, that I should 

 Pure sulphate prepare some very pure sulphate of alumine; a circura- 

 ofalumime stance that enabled me to obtain this sulphate very 

 regularly crystallized, a state in which it had not yet been 

 known, since its concentrated solution yields only lamellar, 

 micaceous crystals, always of an irregular figure. I have 

 had the honour of showing crystals of this sulphate of 

 alumine to several members of the class, particularly to 

 Air. [lair/, who was very desirous of adding a specimen of 

 this sulphate to his valuable collection. 



In 



