4(80 Messrs. Playfair and Joule our^.^v. 



The correspondence between the observed and calculated 

 results in the preceding table, as far as regards the potash 

 salts, is so striking as to remove any doubt of the basis upon 

 which the calculations are made. It is therefore of interest 

 to consider the results indicated by the table a little more in 

 detail. The first point of remark is, that in every case the 

 ammoniacal salt has one volume greater in solution than the 

 corresponding potash salt. Sulphate of potash possesses two 

 volumes in solution ; sulphate of ammonia divested of one vo- 

 lume for its atom of water possesses three. These volumes 

 are respectively carried through the whole class of double 

 sulphates. The volumes of these double sulphates are made 

 up of the sum of the volumes of their constituent salts, which 

 appear, therefore, to be united unchanged. We saw in the 

 previous section that the magnesian sulphates dissolve in water 

 without increasing its bulk more than is due to their water of 

 combination. The same takes place in their double sulphates, 

 for subtracting the volumes of the atoms of water which have 

 been carried by the sulphates into their union with sulphate 

 of potash, the remainder shows the volumes belonging to the 

 latter salts, as indicated by direct experiment. This is 

 strikingly exemplified also by bisulphate of soda. Sulphate 

 of soda was shown in the last section to possess no volume in 

 solution, and in this acid salt we find that the sulphate of soda 

 has in solution ceased to occupy space, for the resulting vo- 

 lume of the acid salt is only 18 or 9 x 2, which is the atomic 

 volume of sulphate of water, as ascertained by the volume 

 occupied by it in bisulphate of potash and bisulphate of am- 

 monia, and as determined also by a calculation, which we have 

 made, of the volume occupied by hydrated sulphuric acid in 

 a dilute solution, founded upon recorded specific gravities. 



Although the ammoniacal sulphates, on account of their 

 analogy to the potash salts, have been introduced into the 

 above table, it is obvious that the numbers representing their 

 volumes are too wide from the theoretical numbers to be con- 

 sidered multiples of 11. Hydrated sulphate of ammonia af- 

 fects four volumes, 11x4, but the anhydrous salt obeys a 

 different law. On immersing in turpentine 33' 15 grains of 

 anhydrous NH4O, SO3, the increase was I9'6 and 19'5, the 

 mean being 19*55 water-grain measures. This gives 39" 1 as 

 the vol. of the equivalent, and 9'8 x 4 = 39*2. Anhydrous 

 sulphate of ammonia affects, therefore, 4 vol. of ice; and the 

 double salts consist of the magnesian sulphates with 6 equiva- 

 lents of water attached to an equivalent of anhydrous sulphate 

 of ammonia, as will be seen from thefplJlQwipg table of, theif 

 solid volumes and specific gravities. .c,qx9 avie,,:J'JOua bivjvoa /' 



