486 \^"iiMes^s, Playf'air and Joule on 



^>-^The preceding table exhibits various points of great interest 

 ks regards isomorphism. Hydrogen has for a long time been 

 recognised by chemists as equivalent to a magnesian metal; 

 and hence the sulphate of a metal of this class should possess 

 the volume of sulphate of vi^ater. The volume of bisulphate 

 of potash is 55*0 by experiment, which leaves 22*0 for that of 

 sulphate of water, on deducting the volume of sulphate of 

 potash, which is 33"0; and the same result follows when the 

 volume of sulphuric acid is deduced from bisulphate of soda, 

 if we suppose the sulphate of soda to enter that salt with two 

 volumes. Thus we have — dT — 8 x d'^i ,3ji 



_^^^^j^^>lphate of water ... . = 22^^ l^fe^ ^^^^^'"" 

 Sulphate of a magnesian oxide = 22 -f- 11 =2 



-.-r* (ii 



We now see that bisulphate of potash (sulphate of water 

 and sulphate of potash) is exactly equivalent to the double 

 sulphates of the magnesian class. {Vide Section V.) 



Bisulphate of potash (HO, SO3 + KO, SO3) =55 



Sulphate of magnesia and potash(MgO,S03 + KO,SOg)=: 55. 



It is now comprehensible why bisulphate of soda should 

 hiave a volume of 44*0 in the solid state and only of 18*0 in a 

 state of solution ; because sulphate of soda which assumes a 

 volume in the solid state becomes added to the same volume 

 possessed by sulphate of water, while in the state of solution 

 the proper volume of sulphate of soda disappears altogether. 



Bisulphate of ammonia possesses a volume due to a com- 

 bination of sulphate of water and sulphate of ammonia, with 

 a volume of 11x4, and it will be .observed that the same 

 result attends the double sulphates of the magnesian metals 

 with sulphate of ammonia. 



Bisulphate of ammonia (NH4O, SO3 + HO SO3) =66 

 Sulphateofammoniaandcopper(NH40,S03H-CuO,S03) = 66. 



The cause of this singular result is in the mutual conver- 

 tibility of the primitive volumes 9"8 and 11. 



It is very curious to observe the large number of volumes 

 which have disappeared when the salt combines with water. 

 Thus sulphate of alumina in its anhydrous state possesses a 

 bulk equal to 79'2, which has ceased to occupy space in the 

 hydrated salt ; and still more remarkable instances of this are 

 seen in the alums, which add to this the volumes of their alka- 

 line sulphates. A curious result obtained in the examination 

 of the hydrated alums is now explicable. We found that the 

 potash alums took up in solution only the space due to their 

 water ; but that the space occupied by them in the state of 

 salts was one volume in addition to this quantity. In the pre- 



