4S2 Mr. R. Phillips on Nitric Acid, S,-c. 



ness in a platina crucible ; the neutral sulphate of potash re- 

 maining weighed 1S'^ grains, and consequently 21*6 of sul- 

 phuric acid and water were expelled. Now as 88 of sulphate 

 of potash contain 40 of sulphuric acid, 78"4' contain 35'6, 

 which deducted from 52'45, the whole quantity contained in 

 100 grains of the salt, leave 16"85 as the sulphuric acid ex- 

 pelled by heat, with ^'TS of water of crystallization ; it will 

 be observed that the quantity of sulphuric acid separated by 

 heat from the supersulphate, is as near one half that remaining 

 in the neutral salt, as 16*85 to 17"8: the salt in question ap- 

 pears therefore to be sesquisulphate of potash, or to consist of 



Theory. Experiment. 

 3 atoms sulphuric acid . . 120 53-33 52-45 



2 atoms potash 96 42-66 42-80 



1 atom water 9 4'00 4*75 



225 99-99 100-00 

 Or it may be regarded as constituted of 



2 atoms of sulphate of potash 1 76 



1 atom of liquid sulphuric acid 49 



225 

 It is extremely difficult to procure the sesquisulphate of 

 potash free from bisulphate ; and on repeating an attempt to 

 prepare it, as nearly as possible in the mode already described, 

 I procured a large quantity of bisulphate and a small propor- 

 tion of sesquisulphate. I am well aware that different salts 

 are obtainable by using different quantities of water, for the 

 same proportions of acid and base will yield either sulphate, 

 sesquisulphate, or bisulphateof potash ; andlhavefound that in 

 order to procure bisulphate, the solution must be much con- 

 centrated. But I am unacquainted with the precise circumstance 

 to which the production of sesquisulphate is to be ascribed ; it 

 may perhaps be referrible to some peculiarity of temperature 

 in influencing the time of coolinjj. 



In the sesquisulphate subjected to analysis, minute crystals 

 of bisulphate of potash could occasionally be detected ; and 

 very pure bisulphate was obtained by evaporating the resi- 

 dual solution after separating the acicular salt ; and eventually 

 the solution became extremely acid, and ceased to afford cry- 

 stals of any kind. 



When a mixture of crystallized bisulphate and sesqui- 

 sulphate of potash is exposed to the air, while it retains some 

 of the solution from which it was crystallized, a formation of 

 arborescent crystals occurs at the surface. I have not yet col- 

 lected a sufficient quantity of this salt for examination, but it 

 is probably only sesquisulphate. 



LXXIV. Notes 



