Royal Academy of Sciences of Paris. 137 



ence in the degree in which the perchlorate of potash and the 

 perchlorate of soda are soluble. The first, at a temperature of 

 15 C. (59 F.), requires more than sixty times its weight of 

 water to dissolve it, while the latter is remarkably deliquescent, 

 and consequently easily soluble, not only in water, but even in 

 alcohol. In order, therefore, to distinguish and separate these 

 two alkalies, it occurred to M. Serullas that it would be expedient 

 to ascertain the possibility of producing, in the same liquid, a salt 

 from potash, which would be almost insoluble, and one from soda 

 which would be very soluble. Neither hydrochlorate of platina, 

 tartaric acid, nor hydrofluosilicic acid, all of which may be em- 

 ployed to precipitate potash and soda, afforded sufficiently accurate 

 means of obtaining the desired result ; but M. Serullas ascertained 

 that if perchloric acid be poured, drop by drop, into a solution of 

 soda and potash mixed, a perchlorate of potash is instantly precipi- 

 tated ; the perchlorate of soda (or the soda itself, if there be not an 

 excess of acid) remains in the liquid, whence it may be separated 

 by concentrated alcohol, which will precipitate at the same time 

 the small quantity of perchlorate of potash which may remain. A 

 solution of perchlorate of soda, to which potash is carefully added, 

 will instantly precipitate a perchlorate of potash, the soda becomes 

 free, and may be separated by alcohol. Owing to this great differ- 

 ence between the solubility of the perchlorate of potash and that of 

 every other salt having the same base, it is easy to ascertain the ex- 

 istence of potash, either free or combined with other acids, in any 

 saline solution, as the smallest quantity of perchloric acid occasions 

 a precipitation of perchlorate of potash, while the other acids are 

 rendered free, and may be isolated by alcohol. This experiment 

 has been tried with the sulphate, nitrate, chlorate, bromate, mu- 

 riate, and hydrobromate of potash. By this mode of proceeding 

 the simultaneous existence of soda and potash may always be ascer- 

 tained, and it will also be easy to examine the nature of the acid 

 primitively combined with the former, as it may always be isolated 

 by concentrated alcohol. There will also be a great advantage in 

 employing Jthe perchlorate of barytes, and that of silver, (both of 

 which are very soluble,) in cases of combinations of soda and 

 potash with sulphuric acid or hydrochloric acid, as, in both cases, 

 by means of alcohol, all the perchlorate of soda may be obtained 

 on the one hand, and on the other, all the perchlorate of potash, 

 with the sulphate of barytes, or the chlorure of silver, from which 

 the perchlorate of potash may easily be removed by washing it in 

 warm water. The general results of the above experiments are 



1. That perchloric acid forms, with potash, a salt soluble with 

 great difficulty, and requiring for its solution sixty times its own 

 weight of water, at a temperature of 59 F. 



2. That soda forms, with the same acid, a salt very deliquescent, 

 and consequently easily soluble, either in water or even in the most 

 highly concentrated alcohol. Tins fact was previously unknown, j 



