1822.] peculiar Crystals of Sulphate of Potash. 341 
might be a compound of sulphate of potash and sulphate of soda; 
some of these circumstances, it appeared to me, might arise 
from the impurities with which nitre in the state in which it is 
imported is known to abound. 
The crystals are of various lengths; the longest is about 
eight inches, 7-8ths of an inch wide near the base, and about 
half an inch thick ; they suffer no change by exposure to the air. 
To determine whether they contain water of crystallization, of 
which sulphate of potash is well known to be devoid; 100 grains 
were subjected to a strong red heat in a platina crucible; the 
loss amounted scarcely to a grain: it is, therefore, evident that 
the crystals contain no combined water. 
In order to discover whether the crystals contain any excess 
of acid, 100 grains were dissolved in water, the solution reddened 
litmus paper slightly ; two grains of crystallized carbonate of 
soda were added to it; it then ceased to act upon litmus paper, 
and on the addition of two grains more of carbonate of soda, the 
solution reddened turmeric paper strongly. [tis evident, there- 
fore, that this small excess of sulphuric acid was in the state of 
mixture, and not of combination ; indeed from the slight loss 
occasioned by exposure to heat, it was evident that the salt 
could not be bisulphate of potash, nor indeed does the form of 
its crystal more resemble that of the bisalt than of the common 
sulphate. 
‘The salt does not appear to contain any combined chlorine ; 
when nitrate of silver was dropped into a solution of it, it 
became slightly opalescent, but no precipitation occurred. To 
separate solutions of the salt, 1 added ammonia, carbonate of 
ammonia, and carbonate of soda, but no precipitation whatever 
occurred ; therefore, the salt is not a double compound of an 
alkaline and earthy salt. 
To determine whether the crystals are a compound of sul- 
phate of potash and of sulphate of soda, it was necessary only 
to add the equivalent quantity of nitrate of barytes. Hydrogen 
being 1, an atom of sulphate of potash is 88, and that of sul- 
phate of soda 72; consequently a salt constituted as I have 
supposed it possible this might be, would be represented by 
88 + 72 = 160; an atom of nitrate of barytes is 132; there- 
fore 25 grains of the double salt ought to decompose 41:25 grs. 
of nitrate of barytes ; I found, however, that considerably less 
of the barytic salt was sufficient ; for when 40 grains of nitrate 
of barytes had been added to a solution of 25 of the salt, the 
filtered solution gave a copious precipitate on the addition of 
sulphuric acid. 
From these experiments I considered the salt to be mere sul- 
phate of potash. In order to arrive at a knowledge of the form 
of the crystals, I submitted them to the examination of my bro- 
ther, Mr. William Phillips, who has favoured me with the fol- 
lowing statement ; 
